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The response of arrays of magnetic nanoparticles (MNPs) of cubic anisotropy materials (magnetite or iron) to high-frequency (sub-GHz) field is investigated utilizing micromagnetic simulations. Composites of MNPs embedded in dielectric media are of interest as core materials for high-frequency power microconverters with low eddy-current losses. Going beyond the macrospin approximation for MNPs (including internal spin structure), we simulate the magnetization dynamics of arrays of spherical and periodically arranged MNPs under periodic boundary conditions and in the presence of thermal fluctuations of the magnetization within the stochastic thermal field. Analyzing the dependence of the dynamical response on the size of the MNPs, we find the size to be crucial for exciting regular magnetization oscillations at room temperature and reducing hysteresis loss. The efficiency of the dynamical response of composites of high-magnetization-metal (iron) MNPs is compared to that of magnetite nanocomposites. We find the sub-GHz susceptibility of magnetite-containing nanocomposite to be comparable to that of the iron MNPs despite the lower saturation magnetization of Fe 3 O 4 , (at the volumetric ratio of the magnetic phase of 0.13, susceptibility is χ ≈ 1. 6 for 5 nm Fe and ≈ 1. 4 for 12 nm Fe 3 O 4 MNPs at T = 300 K and frequency of 0.1 GHz). • Arrays of superparamagnetic nanoparticles of high anisotropy respond strong to sub- GHz field beyond the regime of linear response up to room temperature. • Nanoparticle diameter (thus, strength of dipolar interactions) is crucial for stabilizing the high-frequency magnetic response at elevated temperatures. • At critically-high nanoparticle diameter, magnetic loss of power rapidly increase. [ABSTRACT FROM AUTHOR]

The intrinsic switching field defined as the minimum field to induce spontaneous magnetic reversal is calculated at finite temperatures for a uniaxially anisotropic single domain particle using a formalism based on the generalized free energy function of the system. For a fine ferromagnetic particle coupled to a constant temperature heat bath, the switching field is smaller than the field predicted by the Stoner-Wohlfarth (SW) theory and the difference is dependent on the direction of the applied field resulting in breaking of the symmetry of the SW astroid. • Broken symmetry of Stoner Wohlfarth astroid at finite temperatures. • Significant thermal reduction of switching field if the applied field is axial. • Temperature invariance of prefactor of Arrhenius law involving free energy barrier. [ABSTRACT FROM AUTHOR]

• Using the coprecipitation method, Ce doped Mg-Ni ferrite nanoparticles were successfully synthesized. • The crystallite size of the synthesized samples lies in the range from 6 nm to 12 nm. • Superparamagnetic nature of the samples makes them a potential material for preparation of ferrofluid. • As Ce3+ ion concentration increases, dielectric constant and loss tangent decreases making them a potential material for microwave-based applications. In this work the effect of Ce3+ ion doping on microstructure, crystallite size, magnetic, optical and dielectric characteristics of Mg 0.5 Ni 0.5 Fe 2-x Ce x O 4 (0 ≤ x ≤ 0.1) ferrite nanoparticles are discussed which are synthesized by using the co-precipitation method. The X-ray diffraction analysis confirms the cubic phase of all the synthesized samples and further confirmation of ferrite structure is supported by Fourier transformed infrared spectroscopy characteristic peaks. The crystallite size was determined in the range of 6 nm to 12 nm with increasing lattice parameter value from 8.347 Å to 8.359 Å on increasing Ce3+ ion doping. High-resolution transmission electron microscopy analysis confirms the spherical shape of the nanoparticles with agglomeration. Magnetic hysteresis curves analysis reveals that saturation magnetization of the Mg-Ni ferrite nanoparticles decreases with increasing Ce3+ ion concentration. Vibrating sample magnetometer analysis confirms the superparamagnetic nature of the synthesized samples. Electron spin resonance spectroscopy confirmed the reduction in g-value and spin relaxation time with increasing Ce3+ ions doping. The band gap increases from 1.79 eV to 2.59 eV with increasing Ce3+ ion doping. The magnetic properties of the synthesized samples make these nanoparticles a potential candidate for the synthesis of ferrofluids and biomedical application. Dielectric study confirms the decrease in dielectric constant (ε′) and loss tangent (tan δ) against increasing frequency with increasing Ce3+ ion concentration making the nanoparticles a potential candidate for the high frequency applications. [ABSTRACT FROM AUTHOR]

Diamond, silicon and germanium are widely used technological materials, whose electron structures are tabulated and understood very well. Yet the detailed picture of various diamagnetic contributions and their interplay with the paramagnetic effect, especially at the ab initio level, due to the complexity of this problem remains largely unknown. In our study, based on the ab initio electron band structure approach, all possible magnetic contributions, including the Langevin (Larmor) diamagnetism and the Van Vleck paramagnetism accounted in the second order of the perturbation treatment, are analyzed quantitatively. The Van Vleck contribution has been adapted to the band structure calculations by performing integration over k -points. Also, the partial diamagnetic contributions of core and valence electrons are obtained and discussed in detail. Of all terms there is only one — the Langevin diamagnetism of the valence electrons, which is not well defined quantitatively due to the contribution from the interstitial region. We discuss possible approaches to partitioning this contribution among neighboring crystal sites, based on the Bader charge separation and introducing the area of depleted electron density, excluded from the integration. Under various assumptions for the interstitial region, we have found that the magnetic susceptibilities for diamond, silicon and germanium lie in the range -13.4/-9.3, -4.7/-4.0 and -8.4/-8.8 (volume values, in units of 1 0 − 7 ), correspondingly. In general, this is consistent with the available experimental values, albeit the numerical uncertainty typically reaches tens of percent. • ab initio (DFT) calculations of magnetic susceptibilities for diamond, silicon and germanium. • all magnetic contributions (Langevin, Van Vleck, core, valence) are analyzed quantitatively. • partitioning Langevin valence contribution among neighboring crystal sites, Bader separation. • Van Vleck contribution is adapted to band structure calculations integrating over k-points. [ABSTRACT FROM AUTHOR]

Six lines ferrihydrite nanoparticles are synthesized following a chemical route. The sample is characterized using x-ray diffractometry, Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Average crystallite size is 5 nm. The sample exhibits superparamagnetic behavior. Magnetization versus magnetic field data in the superparamagnetic region are analyzed considering a distribution in particle size. Temperature dependence of saturation magnetization originating from surface spins and antiferromagnetic susceptibility of particle cores are studied. • Saturation magnetization decreases with increasing temperature. • Magnetization of antiferromagnetic particles is due to uncompensated surface spins. • Surface magnetization of crystals is expected to decrease linearly with temperature. • Temperature variation of saturation magnetization of six lines ferrihydrite is studied. [ABSTRACT FROM AUTHOR]

Evidence for the suppression of collective magnetic behavior of dipolarly interacting Fe nanoparticles is found in Fe-Ag granular multilayers. Interaction of Fe particles separated by an Ag layer is studied as a function of the nominal thickness of the Ag layer. The surprisingly increasing interaction with increasing Ag-layer thickness, verified by memory-effect measurements, is explained by the formation of pinholes in the Ag layer at small Ag thicknesses, allowing direct ferromagnetic coupling between the Fe particles. This coupling may hinder the frustration of superspins favored by dipolar interactions. At larger Ag thicknesses, the Ag layer is continuous without pinholes and frustration leads to the appearance of the superspin-glass state. The effect of increasing interactions correlates well with the growing deviation at low temperatures of the measured field-cooled (FC) magnetization from the interaction-free FC curve calculated by a model based on the relaxation of two-level systems. Similar phenomenon is reported in a recently published paper (Sánchez et al., Small 2022 , 18, 2106762) where a dense nanoparticle system is studied. Here the collective magnetic behavior of the particles due to dipolar interactions is suppressed when the anisotropy energy of the individual particles exceeds a certain threshold. [ABSTRACT FROM AUTHOR]

• Dilute AFM La 2 Fe 0.875 Cr 0.125 GaO 6 nanoparticles were prepared by sol-gel technique. • Crystallize in orthorhombic structure with Pbnm space group. • The particle size ranges from 28 to 62 nm. • Presence of non-interacting SPM clusters at room temperature. • Coercivity exhibits a maximum value of 6.694 kOe at ∼138 K. • Exhibits competing DM interaction and strong uncompensated surface spin effects. Magnetism at the nanoscale is intriguing, but that on the magnetic properties of a dilute antiferromagnetic (AFM) system is rarely studied. Presence of uncompensated spins at the lattice as well as on the nanoparticle surfaces could lead to interesting magnetic behaviour. We present the combined effect of reduction in particle size and dilution of exchange interactions on the magnetic properties of an AFM perovskite oxide. A dilute AFM compound, La 2 Fe 0.875 Cr 0.125 GaO 6 nanoparticles (average particle size ∼ 44.5 (7) nm), has been synthesized where non-magnetic Ga-ions are introduced to interrupt the superexchange pathways. The compound crystallizes in orthorhombic structure with Pbnm space group, where Fe, Cr and Ga ions are distributed randomly in the B-site. DC magnetic studies show superparamagnetic behaviour at room temperature, spin-flop transition and a prominent hysteresis loop with sufficiently high coercivity around 6.69 kOe at ∼138 K. The analysis of thermoremanent and isothermoremanent magnetization curves reveal SPM behaviour at 300 K and 2-dimensional dilute antiferromagnetic in field like nature at 5 K. AC magnetic susceptibility analysis confirms the presence of non-interacting clusters having SPM behaviour with blocking temperature ∼280 K. Furthermore, temperature variation of coercivity shows a Gaussian nature, mainly associated with competing Dzyaloshinskii-Moriya interactions between disordered B-site ions along with strong uncompensated surface spin effects. [ABSTRACT FROM AUTHOR]

Highlights • Discussion of the crystal and magnetic structure of ilmenite Mn 2 FeSbO 6. • Ferrimagnetic transition at T N = 270 K. • Identical zero field and field cooled (ZFC-FC) M vs T curves. • Significant changes in M vs T curves with H and T due to unsaturated moments. • Near-zero coercive field in magnetization M vs applied magnetic field H curves. Abstract In the work presented the magnetic properties of the high pressure ilmenite phase Mn 2 FeSbO 6 are investigated in detail. It is shown that Mn 2 FeSbO 6 ilmenite is ferrimagnetic (T N ≈ 270 K) and exhibits a near-zero coercive field H C. Furthermore, the Mn2+-Mn2+, Fe3+-Fe3+ and Mn2+-Fe3+ magnetic exchange interactions exhibit gradual and continuous variations with temperature and magnetic field. The ferrimagnetic moment is unsaturated even at 120 kOe below the theoretical value of 5 μ B per f.u. [ABSTRACT FROM AUTHOR]

Highlights • Crystallization of magnetic particles from Na 2 O-SrO-Fe 2 O 3 -B 2 O 3 glasses is studied. • Increase of sodium oxide content leads to decrease of crystallization temperatures. • Crystallization of 4 nm maghemite nanoparticles is observed at low temperatures. • Hexaferrite morphology and properties are determined by annealing temperatures. Abstract Magnetic glass-ceramics with composition n Na 2 O-9SrO-6Fe 2 O 3 -8B 2 O 3 (n = 1 and 4) were prepared by fast quenching of the molten oxide mixtures and subsequent thermal treatment of the obtained glasses at 450–950 °C. The samples were investigated by differential thermal analysis, x-ray powder diffraction, electron microscopy, and SQIUD magnetometry. Increasing of the sodium oxide content leads to a significant decrease of the glass transition, devitrification, and melting temperatures. Just above the glass transition temperature (525 °C for n = 1 and 430 °C for n = 4) superparamagnetic γ-Fe 2 O 3 nanoparticles precipitate, which, at elevating annealing temperature, are substituted by thin hexaferrite nanoplatelets with coercivities of 2000–4000 Oe; the annealing at higher temperatures results in crystallization of the submicron hexaferrite particles with a coercivity of up to 6000 Oe. Thus the glass-ceramics are highly applicable sources of non-sintered nanoparticles with various morphologies and magnetic properties. [ABSTRACT FROM AUTHOR]

Highlights • Superparamagnetic zinc ferrite nanoparticles were synthesized by hydrothermal method. • The particles size of the nanoparticles increased as the reaction time increased. • The nanoparticles show superparamagnetic behavior with zero H c and M r. • A considerably high M max value was obtained at this particle size limit. • The mean particle sizes and hence high M max can be tuned by adjusting the reaction time. Abstract Superparamagnetic zinc ferrite nanoparticles with high magnetization were successfully synthesized by hydrothermal method at 110 ° C under different reaction times from 2 to 24 h. Elemental analysis of the nanoparticles determined by inductively coupled plasma atomic emission spectroscopy and energy dispersive X-ray spectrometer results proved that the samples are zinc ferrite. X-ray diffraction (XRD) and Fourier transmission infrared spectroscopy analysis displayed that zinc ferrite nanoparticles were single phase of cubic ferrite. The particles size, d XRD of the nanoparticles calculated from XRD patterns increased as the reaction time increased. From the images of transmission electron microscopy (TEM), the particle sizes, d TEM were also calculated and increased from 6.8 ± 2.5 to 10.6 ± 5.1 nm as the reaction time increased, which were consistent with the d XRD. Magnetic measurements revealed that the magnetization curves of the synthesized nanoparticles show superparamagnetic behavior with zero coercivity and remanence. And, the magnetization values also increased to a maximum value of 30.8 emu/g (measured at 20 kOe) as the particle size increased to ∼10 nm with the increase of reaction time. At this particle size limit, this is a considerable high value compared to the superparamagnetic zinc ferrite nanoparticles studies. Magnetization values were also extrapolated. It is seen that to a certain degree, the average particle sizes of the products and hence high maximum magnetization can be tuned by simply adjusting the parameter, reaction time by hydrothermal process. [ABSTRACT FROM AUTHOR]

Highlights • A simple way to synthesize biocompatible superparamagnetic iron oxide nanoparticles coated with ascorbic acid, tartaric acid and a mixture of them is proposed. • The iron oxide nanoparticles were synthesized and coated with these surfactants in one step by co-precipitation method. • The coating agents successfully protected the core against oxidation since the Ms stayed almost stable (∼62) emu/g by 12 weeks. • It can be seen that coated superparamagnetic nanoparticles have high saturation magnetization as well. • From the MTT assay results, the coated nanoparticles are non-toxic and therefore biocompatible for potential biomedical applications. Abstract A simple way to synthesise biocompatible superparamagnetic iron oxide nanoparticles coated with ascorbic acid, tartaric acid and a mixture of ascorbic acid and tartaric acid is proposed. The iron oxide nanoparticles were synthesized and coated with the surfactants in one step by co-precipitation method at room temperature in air atmosphere. The samples have the characteristic (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0) peaks of cubic spinel structure of iron oxide. Fourier Transform Infrared Spectroscopy analysis revealed that the nanoparticles were coated with the surfactants. The mean physical sizes of core obtained from the transmission electron microscopy images were 7 ± 2 nm. Magnetic measurements by vibrating sample magnetometer indicate that all samples are superparamagnetic at room temperature. And, the saturation magnetization, M s of coated nanoparticles was around 62 emu/g. The effectiveness of the coating on the surface of nanoparticles against oxidation is also an important parameter. The coating agents successfully protected the core against oxidation since the M s stayed almost stable (∼62) emu/g by 12 weeks and then decreased to ∼57 emu/g by 48 weeks. It can be concluded that coated superparamagnetic nanoparticles have high saturation magnetization and high stability against oxidation. Furthermore, the MTT assays were also carried out for cytotoxicity of various concentration of coated nanoparticles by using Hep3B, Saos-2 and HUVEC cell lines. From the MTT assay results, it is observed that the coated nanoparticles are non-toxic for all types of cells investigated and therefore can be biocompatible for potential biomedical applications. [ABSTRACT FROM AUTHOR]

Highlights • The NSF, NEF & CSF samples are prepared by citrate-gel autocombustion method. • X-ray diffraction patterns cubic spinel structure. • The FTIR spectra confirmed the cubic spinel structure by locating A and B-sites. • ZFC & FC curves revealed the superparamagnetic nature of nanoparticle. • CSF attributes the soft magnetic behaviour for soft magnets manufacturing industrial applications. Abstract The Er/Sm-substituted nickel ferrite and Sm-substituted cobalt ferrite nanomaterials were synthesized via citrate-gel autocombustion technique. The diffraction pattern revealed the formation of cubic spinel structure. In addition, the structural parameters such as lattice constant (a), average crystallite size (D) and X-ray density (ρ x) were also evaluated. The surface morphology was analyzed using field emission scanning electron microscope (FESEM) and transmission electron microscopes (TEM). Besides, the low temperature magnetic properties were studied using magnetization versus temperature (M−T) & magnetic field (M−H) curves. The obtained results attributed that the NiSm 0.1 Fe 1.9 O 4 (NSF) and NiEr 0.1 Fe 1.9 O 4 (NEF) samples exhibited the superparamagnetic property pertaining almost zero value of coercivity (H c) and remanence (M r) at 5 K & 300 K. Moreover, the superparamagnetic property was evidenced by zero-field cooled (ZFC) and field cooled (FC) curves. Interestingly, the CoSm 0.1 Fe 1.9 O 4 (CSF) sample performed the soft magnetic behavior with increase of temperature from 5 to 300 K by possessing certain numerical values of H c and M r. [ABSTRACT FROM AUTHOR]

Highlights • Cobalt ferrite nanoparticles were synthesized by co-precipitation in one step. • The magnetization increases as reaction time increases and stirring rate decreases. • The critical size of cobalt ferrite nanoparticles for superparamagnetism is 7 nm. • The maximum magnetization value was 41.0 emu/g with zero H c. • A small H c of 2–5 Oe may offer a potential usage in magnetic hyperthermia applications. Abstract In this study, superparamagnetic cobalt ferrite nanoparticles (SCFNs) were synthesized by co-precipitation in one-step. The synthesis parameters; reaction time and stirring rate, were varied separately while the other parameters were fixed constant to investigate the effect of the parameters on the properties of SCFNs. X-ray diffraction analysis and Fourier transform infrared spectroscopy confirmed that synthesized samples are cobalt ferrite. The magnetization consistently increased with the particle size as the reaction time increased and the stirring rate decreased. While the reaction time was effective on the size of the cobalt ferrite nanoparticles, the stirring rate was also found to have influence on the particle size and thus the magnetization of the nanoparticles. The critical size of cobalt ferrite nanoparticles for superparamagnetic limit with zero coercivity and remanence was found to be around 7 nm and its maximum magnetization value was 41.0 emu/g. When the size of the SCFNs went over 7 nm, the magnetization increased with a small coercivity of 2–5 Oe, which may offer a potential usage in magnetic hyperthermia applications. It was seen that structural properties, especially the particle sizes and corresponding magnetic properties of SCFNs were considerably affected by the parameters of stirring rate and especially reaction time. Therefore, it is seen that SCFNs with desirable properties can be tailored by changing the synthesis parameters and therefore may have the potential to use in biomedical applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Sodium tartrate played a double role to prepared Fe 3 O 4 /Ag NPs. • The Fe 3 O 4 /Ag NPs showed high saturation magnetization. • The catalytic activity of Fe 3 O 4 /Ag NPs was studied. • The composition of Fe 3 O 4 /Ag NPs was unchanged after 5 cycle times. Abstract In this paper, we have demonstrated a facile and environmentally friendly approach to prepare Fe 3 O 4 /Ag nanocomposites (Fe 3 O 4 /Ag NPs) by a two-step method. During the preparation process, neither any other reducing agents nor toxic organic solvents were employed. Firstly, Fe 3 O 4 nanoparticles were prepared by co-precipitation and stabilized with the sodium tartrate. Secondly, Fe 3 O 4 /Ag composite nanoparticles were synthesized by a simple reflux method, which once more using sodium tartrate as a green reducing agent to reduce the AgNO 3 to Ag NPs. The as-prepared NPs were characterized by UV–vis spectrometer, dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer (VSM). Both the sodium tartrate stabilized Fe 3 O 4 nanoparticles (Fe 3 O 4 @ST NPs) and Fe 3 O 4 /Ag NPs showed well dispersed in water and had high superparamagnetism at room temperature, which can be quickly actuated by a small household magnet. More importantly, the Fe 3 O 4 /Ag NPs exhibited excellent catalytic properties both in efficiency and recyclability for the degradation of methyl orange (MO) in the presence of H 2 O 2 and the composition was unchanged after 5 cycle times. [ABSTRACT FROM AUTHOR]

Highlights • The hyperthermic efficiency SAR (H , f) of magnetite nanoparticles (MNP) is presented. • Three samples in water and agar gel with mean core diameters d = 10, 14, 18 nm. • 10 nm sample: the effect of the Brownian motion suppression in gel is negligible. • 14 and 18 nm samples: a significant decrease of the SAR in gel is observed. • Results warn about using MNP water solutions to predict heating efficiency in vivo. Abstract Recent studies on magnetic nanoparticles (MNPs) used for Magnetic Fluid Hyperthermia treatments have shown that Brownian rotation is suppressed when they are confined within a cell. To investigate this effect we conducted a systematic study of the Specific Absorption Rate (SAR) of colloidal suspensions of MNPs in water and gels at different agarose concentration. SAR measurements were conducted by varying the frequency (f = 110–990 kHz) and amplitude (up to 17 kA/m) of the applied alternating magnetic field (AMF). MNP samples with different diameter (d = 10, 14, and 18 nm) were used. Our results show that Néel relaxation dominates SAR with negligible contribution from Brownian motion for smaller MNPs (d = 10 nm). For the largest MNPs (d = 18 nm) we observed a more significant SAR decrease in gel suspensions as compared to those in solution. In particular, when applying AMFs as the ones used in a clinical setting (16.2 kA/m at f = 110 kHz), we measured SAR value of 67 W/g in solution and 25 W/g in gel. This experimental finding demonstrates that investigation of MNPs properties should be conducted in media with viscosity similar to the one found in mammalian tissues. [ABSTRACT FROM AUTHOR]

Highlights • (Mn, Co) co-doped SnO 2 nanoparticles are fabricated by the CPACP technique. • Enhanced magnetization is fulfilled in the co-doped system. • Transition from ferromagnetism to paramagnetism is observed in the co-doped system. • The excessively Mn doping leads to a diamagnetic behavior. Abstract Co and Mn-Co co-doped SnO 2 nanoparticles have been successfully synthesized using a simple technique called as citrate precursor assisted co-precipitation (CPACP). Structural and compositional analyses by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Energy Dispersive X-Ray Fluorescence Spectrometer (EDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed that Co and Mn ions were incorporated into the SnO 2 host lattice without changing the inherent rutile structure. The average crystallite size of the prepared samples were estimated to be in the range of 8–12 nm. In a single Co2+-doped SnO 2 sample, the magnetization was observed to increase as the Co2+ ions concentration increased. The transition metal Mn can adjust the magnetic signal of the Co2+-doped SnO 2 sample, which is subject to the concentration of Mn dopant. Adding a proper amount of Mn to the Co2+-doped SnO 2 sample enhanced the magnetization. As the Mn2+ ions concentration increases, the magnetic properties of the (Mn, Co) co-doped SnO 2 nanoparticles gradually shift from ferromagnetic behavior to superparamagnetism. However, the sample Sn 0.83 Mn 0.12 Co 0.05 O 2 exhibits diamagnetic behavior when the concentration of Mn2+ ions is doped excessively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The observed unusual co-existence of AFM with GP in nanometric SCCMO sample is rare in nature. • The glassy behavior in bulk SCCMO is attributed to the antisite disorders (∼7.12%) along with magnetic frustration. • Magnetic spin dynamics and aging effect are suggesting different spin relaxation processes. Abstract Griffiths phase like behavior has been investigated in details in size modulated Sm 1.5 Ca 0.5 CoMnO 6 double perovskite, having ferromagnetic entities in the paramagnetic matrix. Temperature dependent real and imaginary part of ac susceptibility confirms that Sm 1.5 Ca 0.5 CoMnO 6 -1150 °C bulk-sample has spin-glass like ordering below T g ∼ 34.88(3) K. This glassy behavior is attributed to the antisite disorders (∼7.12%) along with and magnetic frustration in the system. However, the ground state of Sm 1.5 Ca 0.5 CoMnO 6 -600 °C nanometric-sample is observed to be antiferromagnetic in nature due to the presence of large antisite disorder (∼53.58%). The observed unusual co-existence of antiferromagnetism with Griffiths-like phase in Sm 1.5 Ca 0.5 CoMnO 6 -600 °C sample is rare in nature. Interesting magnetic spin dynamics and aging effect are also observed in both the compounds suggesting different spin relaxation processes in low temperature regime. The observed magnetism in these compounds can be tuned by nearest neighbor Co-O-Mn and/or Co-O-Co/Mn-O-Mn exchange interactions as well as the next nearest neighbor Co-O-O-Co/Mn-O-O-Mn interactions. [ABSTRACT FROM AUTHOR]

Abstract This article comprises of the structural, magnetic, magneto-caloric and critical behavior study of single phase perovskite manganite LaMnO 3+δ sample synthesized by traditional Solid State route. X-ray powder diffraction (XRD) at room temperature indicates the single phase trigonal crystalline structure of LaMnO 3+δ with hexagonal setting R 3 ‾ c. Magnetic, magnetocaloric and critical behavior are studied using temperature dependent magnetization (M−T) and applied magnetic field dependent magnetization (M−H) data probed by Physical Property Measurement System (PPMS). The second order ferromagnetic to paramagnetic (FM-PM) phase transition is observe at Curie temperature (T C ∼ 180 K). This phase transition is responsible for maximum entropy change (Δ S M max ) of 0.451(1) J/kg K at applied magnetic field of 6 Tesla with relative cooling power (RCP) of 54.293(5) J/kg. At T C , the order of magnetic phase transition is examined by employing Modified Arrott plots (MAP), Kouvel Fisher (KF) and simple isotherm analysis technique. The obtained values of critical exponent’s β ≈ 0.365 ± 0.06, γ ≈ 1.14 ± 0.04 and δ ≈ 4.16 ± 0.10 elaborate that the magnetic phase transition coordinated well with the 3D-Heisenberg model at T C ≈ 180 K and are confirmed by scaling equations of state. Similarly the change in magnetic entropy (ΔS M) versus applied magnetic field recorded complies with the power law ΔS = (H)n with n = 0.64 at T C = 180 K. [ABSTRACT FROM AUTHOR]

Abstract Bulk cobalt ferrite, being a hard ferrite, shows high magnetization, high resistivity and high coercivity. If thin films of cobalt ferrite can be deposited at a low enough temperature and if its coercivity can be reduced, cobalt ferrite will make a very good candidate for use as a magnetic core of an integrated inductor in RF-CMOS ICs. Though polycrystalline and epitaxial thin films of cobalt ferrite have been made by various techniques, there are no reports of thin films of superparamagnetic cobalt ferrite. In this work, nanocrystalline cobalt ferrite thin films, which are superparamagnetic as deposited, have been prepared in the solution medium at ∼190 °C, using microwave irradiation. The as-prepared films have a saturation magnetization (M S) of 401 emu/cc and coercivity (H C) of 19 Oe at room temperature for a crystallite size of 2 nm. The cobalt ferrite powder obtained as a by-product during the same process has M S of 50 emu/g and H C of 5 Oe at room temperature, making it superparamagnetic. The as-prepared films were annealed in air at 300 °C for 5 min and 10 min. Annealing for 10 min results in an increase in crystallite size to 36 nm, M S increases from 401 emu/cc to 545 emu/cc, and H C increases from 19 Oe to 860 Oe. The change in magnetic properties can be directly associated with change in the crystallite size and degree of crystallographic inversion, as determined by neutron diffraction and deduced from X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Highlights • A series of Ni 1.5 [Fe(CN) 6 ] x [Cr(CN) 6 ] 1-x ·nH 2 O (x = 0, 0.25, 0.5, 0.75, 1) is studied. • The properties of the materials change in the regular way with the change of x. • The values of MCE varies between 2.4 J·mol−1K−1 and 3.5 J·mol−1K−1 at Δ H = 50 kOe. • MCE and a RPC are comparable to those of the intermetallic materials. • Scaling behaviour of the magnetocaloric effect is discussed. Abstract A comprehensive study of structural, magnetic and magnetocaloric properties in the ternary Prussian blue analogue (PBA) Ni 1.5 [Fe(CN) 6 ] x [Cr(CN) 6 ] 1-x ·nH 2 O (x = 0, 0.25, 0.5, 0.75 and 1) is presented. For all compounds the second-order magnetic phase transition from high temperature paramagnetic to the low temperature ferromagnetic state at the Curie temperature (T c) is observed. We show the possibility of tuning the magnetic and magneto-caloric properties of PBA materials by changing the compositional factor of the metal centres involved in the cyano-bridging. An increase in Fe content leads to increase in the coercive field, whereas the critical temperature decreases from 60 to 22 K. The magnetic entropy change Δ S , as well as the related Relative Cooling Power (RCP), vary with x parameter in the regular way. The highest value of Δ S was observed for sample with x = 1 and was equal to 3.49 J mol−1K−1 under a magnetic field of 50 kOe, whereas the RCP varied from 62 J mol−1 (145.35 J kg−1) to 118 J mol−1 (273.33 J kg−1), when x decreased from 1 to 0. [ABSTRACT FROM AUTHOR]

Highlights • This study investigates the magnetic properties of rutile TiO 2 implanted with cobalt ions. • SPM behavior here is highly anisotropic coupled with magneto-crystalline anisotropy of the Ti 1−x Co x O 2. • The Co nanoclusters possess an easy and hard axis of magnetization. • The M-T variation reveals the prominent role of dipole and inter-cluster exchange interaction. • Highly anisotropic nature of the SPM presents applications in magnetic switching devices. Abstract The present study investigates the magnetic properties of single crystal rutile TiO 2 (110) implanted with cobalt ions for fluences between 5 × 1016 and 1 × 1017 ions/cm2 with energy of 200 keV. The temperature and field dependent magnetization for magnetic fields along [0 0 1] and [ 1 1 ¯ 0 ] directions of the as implanted TiO 2 crystals show anisotropic super-paramagnetic behaviour due to formation of Co (hcp) nano-clusters unlike the complete ferromagnetic behaviour from previous reports. The ZFC and FC magnetization curves show a much higher blocking temperature ( T B ) along [ 1 1 ¯ 0 ] with values ranging from 30 to 150 K, while for field along [0 0 1] shows a lower T B ranging from 8 to 70 K. The magnetization isotherms above T B show a sharper rise and universal scaling behaviour, for field along [ 1 1 ¯ 0 ] direction. At 2 K, M - H curves show hysteresis behaviour similar of easy and hard axis of a ferromagnet. The magnetic anisotropy of Co nano clusters are coupled by the magneto crystalline anisotropy of secondary phases of cobalt with TiO 2 , thus indicating the highly oriented nature of the Co clusters. Role of dipole interactions and inter cluster exchange interactions have also been discussed. [ABSTRACT FROM AUTHOR]

Permanent magnet materials based on the MM 2 Fe 14 B (MM = Misch-metal) are widely noted. However, as a room temperature paramagnetic phase, the existence of CeFe 2 phase in MM 2 Fe 14 B alloy is unavoidable. In order to eliminate the CeFe 2 phase, the La substitution on MM in MM 2 Fe 14 B alloys was described. Alloys with nominal composition of (La x MM 1−x ) 33 Fe 66 B (x = 0, 0.025, 0.05, 0.075, 0.1, 0.15) were prepared, and the crystal structure and magnetization of the (La x MM 1−x ) 33 Fe 66 B alloys were investigated. XRD results reveal that the lattice parameter a, c, unit-cell volume V, and c/a ratio of (La x MM 1−x ) 33 Fe 66 B alloys increase linearly with the La increase, indicating that La atoms enter into the main phase. Key to this study is the finding that CeFe 2 phase disappears with the La content above 0.075. It is therefore concluded that La substitution could inhibit formation of CeFe 2 phase. This is consistent with the observation from SEM-EDS. Another interesting finding is that La substitution would cause the change of Nd, Pr, La and Ce ratio in main phase, which means the ratios of four rare earth elements change with the La substitution. With the increase of x, the (Pr + Nd)/(La + Ce) ratio in main phase of (La x MM 1−x ) 33 Fe 66 B alloys decreases first, showing the lowest point at x = 0.075, and then increases. As a result, the saturation magnetization (M s ) of (La x MM 1−x ) 33 Fe 66 B alloys has the same tendency, which decreases from 11.78 kG (x = 0) to 11.35 kG (x = 0.075) first, and then increases to 11.96 kG (x = 0.15). And the Curie temperature (T c ) displays the same trend compared to the M s . These facts show that the MM has a great potential to prepare the low cost sintered permanent magnets. [ABSTRACT FROM AUTHOR]

The colloidal nanoparticles Fe m O n –SiO 2 have been obtained using the sol–gel method. Based on the data obtained with transmission electron microscopy and dynamic light scattering, a lognormal size distribution of nanoparticles with an average size of 20–30 nm have been constructed. The shape of Mössbauer spectra implies that they have the characteristic relaxation time of the order of 10 –9 –10 –10  s that corresponds to the grain size of about 10 nm. X-ray diffractometry indicates that the crystalline phase of the particles is magnetite. Hysteresis loops have been traced with a vibration sample magnetometer and the demagnetization curve of anhysteretic remanent magnetization measured with a SQUID magnetometer. Theoretical analysis of magnetization data based on a model of magnetostatically interacting superparamagnetic nanoparticles confirms the presence of both separate superparamagnetic magnetite particles (less than 20 nm in size) and those organized into clusters with an average size of about 30 nm. [ABSTRACT FROM AUTHOR]

Cobalt ferrite nanoparticles were synthetized by co-precipitation technique from nitrate precursors. X-ray diffraction confirms the formation of the spinel ferrite. SEM and HRTEM micrographs corroborate the formation of agglomerated nanoparticles of 8–35 nm size range with 21.7 nm average size. The broad size distribution and considerable agglomeration of the particles hamper the superparamagnetic state of the sample, provoking a weak coercivity at room temperature. In contrast to several other magnetic nanostructures, the ZFC-FC curves of cobalt-ferrite nanoparticles revealed an unusually large magnetostriction, evidenced by larger values of magnetization in their ZFC curves than the FC curves in the measured temperature range 20–375 K. The behavior could be reversed on applying high magnetic fields. However, the maximum of ZFC curve reduces on increasing the applied magnetic field. [ABSTRACT FROM AUTHOR]

The response of composites of magnetic nanoparticles (MNPs) with randomly-oriented magnetocrystalline anisotropy axes to a linearly-polarized ac field or a rotating field is studied with regard to the concept of using superparamagnetic nanocomposites as core materials for high (sub-GHz and GHz) frequency power conversion devices. We perform micromagnetic simulations of systems of spherical 5nm-diameter nanoparticles of Fe 65 Co 35 with two different concentrations arranged periodically within a dielectric matrix, including thermal fluctuations of the magnetization within the stochastic thermal field. Because the particles are closely packed, the effect of surface anisotropy is neglected. The dependence of the amplitude of the magnetic response function on temperature is determined. We show the inapplicability of Brown's classic theory of thermal excitations in single-domain magnetic particles for given material parameters even in the absence of the magnetostatic field. Magnetostatic interactions of MNPs are found to be necessary for stabilizing the dynamical magnetic response in the high temperature (low-energy-barrier) range. They allow for driving magnetization oscillations at room temperature with amplitude comparable to the zero-temperature case. Dynamical (hysteretic and residual) losses are discussed. • Arrays of superparamagnetic nanoparticles of 5 nm diameter respond strong to sub-GHz field up to room temperature. • A bias field perpendicular to the driving field allows for reducing thermal fluctuations of the magnetization of arrays. • Rotating field drives similar magnetic response as linearly-polarized field. [ABSTRACT FROM AUTHOR]

Calcium ferrite nanoparticles with average crystallite size of ∼11 nm have been synthesized by sol-gel method by mixing calcium and ferric nitrates in stoichiometric ratio in the presence of ethylene glycol. As-synthesized nanoparticles were annealed at different temperatures and their structural and magnetic properties have been evaluated. X-ray diffraction studies showed that unlike most ferrites, as-synthesized cubic calcium ferrite showed a slow transformation to orthorhombic structure when annealed above 400 °C. Single phase orthorhombic CaFe 2 O 4 was obtained upon annealing at 1100 °C. Divergence of zero field cooled and field cooled magnetization curves at low temperatures indicated superparamagnetic behavior in cubic calcium ferrite particles. Superparamagnetism persisted in cubic samples annealed up to 500 °C. As-synthesized nanoparticles heat treated at 1100 °C exhibited mixed characteristics of antiferromagnetic and paramagnetic grains with saturation magnetization of 0.4 emu/g whereas nanoparticles calcined at 400 °C exhibited superparamagnetic characteristics with saturation magnetization of 22.92 emu/g. An antiferromagnetic to paramagnetic transition was observed between 170 and 190 K in the sample annealed at 1100 °C, which was further confirmed by Mössbauer studies carried out at different temperatures across the transition. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles (MNPs) are widely used in biomedical applications. Characterizing dilute suspensions of superparamagnetic iron oxide nanoparticles (SPIONs) in bio-relevant media is particularly valuable for magnetic particle imaging, hyperthermia, drug delivery, etc. Here, we study dilute aqueous suspensions of single-domain magnetite nanoparticles using an AC Faraday rotation (FR) setup. The setup uses an oscillating magnetic field (800 Hz) which generates a multi-harmonic response. Each harmonic is collected and analyzed using the Fourier components of the theoretical signal determined by a Langevin-like magnetization. With this procedure, we determine the average magnetic moment per particle μ , particle number density n , and Verdet constant of the sample. The fitted values of μ and n are shown to be consistent across each harmonic. Additionally, we present the results of these parameters as n is varied. The large values of μ reveal the possibility of clustering as reported in other literature. This suggests that μ is representative of the average magnetic moment per cluster of nanoparticles. Multiple factors, including the external magnetic field, surfactant degradation, and laser absorption, can contribute to dynamic and long-term aggregation leading to FR signals that represent space- and time-averaged sample parameters. Using this powerful analysis procedure, future studies are aimed at determining the clustering mechanisms in this AC system and characterizing SPION suspensions at different frequencies and viscosities. [ABSTRACT FROM AUTHOR]

Due to advancements in nanomagnetism and latest nanomagnetic materials and devices, a new potential field has been opened up for research and applications which was not possible before. We herein propose a new research field and application for nanomagnetism for the visualization of dynamic magnetic fields in real-time. In short, Nano Magnetic Vision. A new methodology, technique and apparatus were invented and prototyped in order to demonstrate and test this new application. As an application example the visualization of the dynamic magnetic field on a transmitting antenna was chosen. Never seen before high-resolution, photos and real-time color video revealing the actual dynamic magnetic field inside a transmitting radio antenna rod has been captured for the first time. The antenna rod is fed with six hundred volts, orthogonal pulses. This unipolar signal is in the very low frequency ( i.e. VLF ) range. The signal combined with an extremely short electrical length of the rod, ensures the generation of a relatively strong fluctuating magnetic field, analogue to the signal transmitted, along and inside the antenna. This field is induced into a ferrolens and becomes visible in real-time within the normal human eyes frequency spectrum. The name we have given to the new observation apparatus is, SPIONs Superparamagnetic Ferrolens Microscope (SSFM), a powerful passive scientific observation tool with many other potential applications in the near future. [ABSTRACT FROM AUTHOR]

Fe-doped BaTiO 3 has been prepared by the solid state reaction method. Nanonization of sample has been achieved by using high energy ball milling. Tetragonal phase along with a small amount of hexagonal phase has been identified by room temperature X-ray diffraction (XRD) technique in all the samples. Mössbauer spectrum of the as-prepared sample shows multi-site substitution of Fe atoms. Magnetic interactions between Fe atoms placed at three different configurations have been evidenced by the presence of three sextets. A doublet pattern has also been observed for Fe atoms situated in isolate manner without any magnetic exchange. Suppression of sextet patterns in milled samples has been attributed to the presence of superparamagnetism. [ABSTRACT FROM AUTHOR]

In this work, well-dispersed nanoparticles of NiFe 2 O 4 with diameters less than 10 nm and good crystallinity and excellent magnetic properties were synthesized via a simple one-step capping agent-free coprecipitation route from metal chlorides. The ammonia was used as the precipitating agent and also the solution basicity controller. The effect of pH value during the coprecipitation process was investigated by details through microstructural, optical and magnetic characterizations of the synthesized particles using X-ray diffraction, transmission electron microscopy, Fourier transform infrared and UV–vis spectroscopy, and vibrating sample magnetometer. The results showed that the particle size, departure from the inverse spinel structure, the band gap value and the magnetization of Ni ferrite samples increase with pH value from 9 to 11 indicating the more pronounced surface effects in the smaller nanoparticles. [ABSTRACT FROM AUTHOR]

The macroscopic magnetic moment of a superparamagnetic system has to overcome an energy barrier in order to switch its direction. This barrier is formed by magnetic anisotropies in the material and may be surmounted typically after 10 9 - 10 12 attempts per second by thermal fluctuations. In a first step, the associated switching rate may be described by a Néel-Brown-Arrhenius law, in which the energy barrier is assumed as constant for a given temperature. Yet, magnetic anisotropies in general depend on temperature themselves which is known to modify the Néel-Brown-Arrhenius law. We illustrate quantitatively the implications of a temperature-dependent anisotropy on the switching rate and in particular for the interpretation of the prefactor as an attempt frequency. In particular, we show that realistic numbers for the attempt frequency are obtained when the temperature dependence of the anisotropy is taken into account. [ABSTRACT FROM AUTHOR]

Pseudo-one-dimensional Chevrel compound TlFe 3 Te 3 undergoes a first-order phase transition from paramagnetic to ferromagnetic at T C = 220 K. Here we report a systematic study of magnetization, heat capacity and resistivity on polycrystalline TlFe 3 Te 3 near T C . The enhancements of T C in an external magnetic field and a hydrostatic pressure follow the Clausius-Clapeyron relations. The large enhancement of the T C under the pressure indicates that the unit cell shrinks from para- to ferro-magnetic phase. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles are promising systems for biomedical applications and in particular for Magnetic Fluid Hyperthermia, a therapy that utilizes the heat released by such systems to damage tumor cells. We present an experimental study of the physical properties that influences the capability of heat release, i.e. the Specific Loss Power, SLP , of three biocompatible ferrofluid samples having a magnetic core of maghemite with different diameter d = 10.2, 14.6 and 19.7 nm. The SLP was measured as a function of frequency f and intensity H of the applied alternating magnetic field, and it turned out to depend on the core diameter, as expected. The results allowed us to highlight experimentally that the physical mechanism responsible for the heating is size-dependent and to establish, at applied constant frequency, the phenomenological functional relationship SLP = c·H x , with 2 ≤ x <3 for all samples. The x -value depends on sample size and field frequency, here chosen in the typical range of operating magnetic hyperthermia devices. For the smallest sample, the effective relaxation time τ eff ≈ 19.5 ns obtained from SLP data is in agreement with the value estimated from magnetization data, thus confirming the validity of the Linear Response Theory model for this system at properly chosen field intensity and frequency. [ABSTRACT FROM AUTHOR]

In this work, we report the structural and magnetic properties of nanocrystalline Cu 1−x Zn x Fe 2 O 4 mixed ferrites synthesized using novel combustion method. The prepared samples are spinel structured and the secondary phase α-Fe 2 O 3 is also present in CuFe 2 O 4 . The size of the crystallites ranges between 9.6 nm and 31 nm and the lattice constant increases from 8.342 Å to 8.435 Å. The FTIR absorption bands of CuFe 2 O 4 are observed at 571 cm −1 and 409 cm −1 for tetrahedral and octahedral sites, respectively. These bands are shifting to 547 cm −1 and 397 cm −1 for Zn substitution. Raman spectra show the change in local environment of tetrahedral and octahedral interstitial sites with Zn. The FE-SEM images show that the prepared samples are nano sized and the substitution of Zn decreases the agglomeration. The magnetic study reveals that the saturation magnetizations initially increases from 21.45 emu/g (x = 0) to 44.16 emu/g (x = 0.2) and then decreases at 300 K. The superparamagnetic behavior is observed for samples of x ≥ 0.4 concentration. The temperature dependent zero field cooled and field cooled magnetic measurements confirm the superparamagnetic nature and the observed blocking temperature decreases from 120.4 K to 32.3 K. The hysteresis curves measured at 20 K show the coercivity and it varies from 663 Oe to 70 Oe for increasing Zn content. [ABSTRACT FROM AUTHOR]

The nanohyperthermia investigation of superparamagnetic La 0.77 Sr 0.23 MnO 3 nanoparticles synthesized by hydrothermal method has been carried out. The synthesized nanoparticles are found to be highly uniform in size and shape with average particle size 18 nm. Structural analysis confirms the pseudo-cubic perovskite crystal structure with space group of ( R 3 c ). The magnetization versus applied magnetic field (M-H) hysteresis loops measurements revealed the superparmagnetic nature of the synthesized nanoparticles. The induction heating of synthesized nanoparticles for their applications in nanohyperthermia has been studied. The in vitro cytotoxicity test of the synthesized superparamagnetic nanoparticles has been probed by evaluating the viability of HeLa (Human Negroid Cervix Epitheloid Carcinoma) cell lines. The mechanism responsible for nanohyperthermia heating of the synthesized nanoparticles has been discussed. [ABSTRACT FROM AUTHOR]

Methods improving the chemical and physical stability of magnetic nanoparticles are important in diverse research disciplines such as catalysis, magnetic resonance imaging, biomedicine, and bioseparation. It is essential that defined nanomaterial characteristics remain unchanged from the start of the nanoparticle production to their final application. A simple, fast and reliable strategy based on a thermal decomposition approach was established to design highly and uniformly loaded iron oxide-shell silica-core nanocomposites. They are formed by maghemite nanoparticles (8.4 ± 1.0 nm) uniformly deposited on mesoporous silica nanoparticles (381 nm ± 111 nm). Their magnetic properties as well as chemical, and mechanical stability were verified by SQUID magnetometry, Raman microspectroscopy, and electron microscopy (SEM and TEM), respectively. The produced superparamagnetic nanocomposites were stable over several months. The coating with organosilanes enables the transfer from nonpolar to aqueous phase which makes the magnetic nanocomposites also applicable for life sciences. [ABSTRACT FROM AUTHOR]

Mn 1-x Zn x Fe 2 O 4 nanoparticles ( x = 0.1, 0.3, 0.5, 0.7 and 0.9) were synthesized using chemical co-precipitation method. X-ray diffraction (XRD) analysis confirmed the cubic spinel structure of synthesized nanoparticles. The crystallite size and lattice parameter were found to decrease with increase in zinc substitution. Surface morphology by scanning electron microscope (SEM) and energy dispersive analysis of X-ray (EDAX) confirmed the presence of substituted metal ions in all the samples. Magnetic parameters at room temperature using vibrating sample magnetometer (VSM) are found to decrease with increasing zinc substitution. Faraday rotation of Mn 1-x Zn x Fe 2 O 4 nanoferrofluids is found to vary with zinc substitution under applied magnetic field. Verdet constant obtained from Faraday rotation are found to vary from 5.35 to 2.71 deg./T cm with zinc substitution. [ABSTRACT FROM AUTHOR]

Numerical calculations of magnetic properties of Pr 3+ ions in crystal field of the mixed (hexagonal + orthorhombic) symmetry in PrNi 5− x Cu x pseudobinary alloys are presented. The molecular field theory and the crystal field theory in the point charge model are used in calculations. It is shown that the admixing of crystal field of orthorhombic symmetry to the original hexagonal crystal field of PrNi 5 and PrCu 5 compounds leads to an abrupt increase in their magnetic susceptibility followed by the onset of ferromagnetism, which was earlier observed experimentally in pseudobinary PrNi 5− x Cu x alloys. The calculated dependences of magnetic moments of Pr 3+ ions in crystal fields of the mixed symmetry on the magnetic field strength and temperature satisfactorily agree with the experimental results for PrNi 5− x Cu x alloys. [ABSTRACT FROM AUTHOR]

We report on structural, spin glass behaviour and competing magnetic interactions in xNiFe 2 O 4 - (1-x)BaTiO 3 (x = 0.2 and 0.3) nanocomposites prepared by sol-gel method. The structure and surface morphology of the NiFe 2 O 4 -BaTiO 3 composites were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD measurements of composite materials show the presence of both NiFe 2 O 4 and BaTiO 3 phases. FESEM and energy dispersive X-ray (EDX) measurements indicate uniformly distributed nano size particles and presence of Ni, Fe, O, Ba and Ti elements respectively. Temperature variation Raman spectra indicates large structural disordering (Peak broadening and shift) around 395 K due to the structural transformation of BaTiO 3 . Magnetization, zero field cooled (ZFC) and field cooled (FC) measurements were carried out from 2 K to 320 K for both composites. ZFC and FC measurements reveal the spin glass and Superparamagnetism like behaviour along with competing magnetic interaction in both composites. Saturation magnetization value is seen to increase from 6.7 to 10 emu/g with increasing Ni ferrite composition from x = 0.2 to x = 0.3. Distribution function associated with magnetocrystalline anisotropy energy barrier exhibits broad peaks due to the random distribution of spins associated with different particle size in the x = 0.3 composition. [ABSTRACT FROM AUTHOR]

• Polycrystalline specimens of Ba 2 Y 1- x Cu x TaO 6-δ were synthesized by the solid-state reaction route. • The magnetic properties of the Ba 2 Y 1- x Cu x TaO 6-δ solid solutions were investigated and reported for the first time. • The Cu for Y substitution induces paramagnetism and the onset of antiferromagnetic correlations. We carried out a study of the structural and magnetic properties of Ba 2 Y 1- x Cu x TaO 6- δ (0.0 ≤ x ≤ 0.5) compounds. The cubic rock-salt double perovskite structure of Ba 2 YTaO 6 is retained upon the partial substitution of Cu for Y up to x = 0.50 and the lattice parameter a drops at the rate of da/dx ≈ −0.17 ± 0.01 Å/%Cu. While the effective moment μ eff and the Curie-Weiss temperature θ CW are nearly negligible in Ba 2 YTaO 6 , the partial substitution of Cu for Y results shows an increase in μ eff at the rate of ≈ 1.9 ± 0.2 µ B /%Cu, consistently with the paramagnetic behavior expected for Cu2+, and a decrease in θ CW at the rate of −16 ± 2 K/%Cu. The drive of θ CW towards more negative values is suggestive of the onset of antiferromagnetic correlations. [ABSTRACT FROM AUTHOR]

• Non-stoichiometric Zn 0.5 Ca 0.5 Fe 2 O 4 ferrite nanoparticles exhibit dominant superparamagnetic character at 300 K. • Relaxation dynamics accompanied by ageing, memory and rejuvenation establishes superspin glass coexisting with superparamagnetism at low temperatures in ZCF NPs. • Dipolar inter-particle interactions, randomness in anisotropic & positional distributions along with exchange bias leads to superspin glass phase in ZCF NPs. In this manuscript, we report the coexistence of superparamagnetic-super spin glass phase in aggregated non-stoichiometric Zn 0.5 Ca 0.5 Fe 2 O 4 ferrite nanoparticles (ZCF NPs). A polycrystalline sample of ZCF NPs was synthesized by the self-ignition sol–gel route and characterized using a variety of techniques. Extensive temperature, field and wait-time dependent dc-magnetization & ac-susceptibility measurements were performed for elucidating the magnetism of ZCF NPs. M−H & Mössbauer data at 300 K and M−T curves in ZFC & FC protocols revealed that ZCF NPs exhibit dominant superparamagnetic (SPM) character at 300 K with M s = 16 emu/g & T B ∼ 120 K. Magnetically disordered surface over a single domain core of ZCF NPs has been established by the shift in coercivity at 5 K in ZFC and FC protocols. ZFC magnetization for a single stop and wait protocol exhibited an ageing dip at the stop temperature (72 K) with waiting time. It is shown that the in-phase peak of ac-susceptibility vs. temperature curves shifts towards higher temperature with driving frequencies and obeys dynamic scaling & Vogel-Fulcher law. These findings affirmed presence of glassy states in ZCF NPs due to interacting magnetic nanoparticles. On cooling the random ensemble of ZCF NPs, interparticle dipolar interactions lead to genesis of glassy behaviour, which is identified as superspin glass (SSG). Observation of memory and rejuvenation in a quasi-equilibrium magnetic state due to the collective nature of low-temperature spin dynamics differ ZCF NPs from canonical spin-glass. Extensive magnetic studies on ZCF NPs revealed a crossover of SPM to SSG phase just below T B at 115 K due to the random distribution of magnetic momenta, anisotropy and interparticle interactions. [ABSTRACT FROM AUTHOR]

We have studied the effect of replacing Mn 3+ by Cr 3+ on the structure, transport and magnetism in the bilayered manganite LaSr 2 Mn 2 O 7 . Although no structural transition was observed in LaSr 2 Mn 2−y Cr y O 7 (0.1 ≤ y ≤ 0.6), the electrical transport and the magnetic properties were found to be affected significantly by this substitution. Substitution of Cr 3+ reduces the conductivity by restricting the hopping of small polarons. Magnetization increases with increasing Cr 3+ concentration suggesting that Cr 3+ -ions induce ferromagnetic moments . The ferromagnetic and an antiferromagnetic phase observed above ∼60 K merge into an inhomogeneous phase below this temperature. Thermopower yields an essentially concentration independent charge density nearly equal to its value for chromium free composition inspite of its expected decrease with this substitution suggesting that the small charge density of the insulating AFM phase is supplemented by the free carriers in the FM phase. The inhomogeneous phase shows a relaxor type behavior which contrasts with the spin glass behavior seen in La 0.46 Sr 0.54 Mn 0.98 Cr 0.02 O 3 having an identical AFM magnetic state. The difference is attributed to the non-JT character of Cr-ions which reduce the distortion of the Mn O octahedra located within the FM domains. With a higher lattice strain in the surrounding AFM matrix the carriers remain confined within the FM domains leading to the relaxor type behavior. [ABSTRACT FROM AUTHOR]

Manganese ferrite (MnFe2O4) nanoparticles were synthesized by sol-gel auto-combustion method using manganese nitrate and ferric nitrate as precursors and citric acid as a fuel. Scanning electron micrographs show irregularly shaped morphology of the particles. The as-prepared samples were annealed at 400, 500, 600 and 800 °C for 2 h in air. The phase identification and structural characterizations were performed using powder X-ray diffraction technique along with Mössbauer spectroscopy. Magnetization loops and 57Fe Mössbauer spectra were measured at RT. After annealing the sample at or below - 500 °C, we observed two different spinel phases corresponding to two different lattice parameters. This is originating due to the partial oxidation of Mn2+ to Mn3+. At high annealing temperatures (- 600 °C or above) the spinel MnFe2O4 phase decomposes into crystalline α-Mn2O3 and α-Fe2O3 phases, and amorphous FeO phase. [ABSTRACT FROM AUTHOR]

Nanocrystalline Fe-Pt alloys have been synthesized via chemical reduction route using various capping agents; such as: oleic acid/oleylamine (route-1) and oleic acid/CTAB (route-2). We could able to synthesize Fe50Pt and Fe54Pt alloys via route 1 and 2, respectively. As-prepared Fe-Pt alloys crystallize in disordered fcc phase with crystallite sizes of 2.3 nm and 6 nm for route-1 and route-2, respectively. Disordered Fe-Pt alloys were transformed to ordered fct phase after annealing at 600 °C. SEM studies confirm the spherical shape morphologies of annealed Fe-Pt nanoparticles with SEM particle sizes of 24.4 nm and 21.2 nm for route-1 and route-2, respectively. TEM study confirms the presence of 4.6 nm particles for annealed Fe50Pt alloys with several agglomerating clusters of bigger size and appropriately agrees well with the XRD study. Room temperature magnetization studies of as-prepared Fe-Pt alloys (fcc) show ferromagnetism with negligible coercivities. Average magnetic moments per particle for as-prepared Fe-Pt alloys were estimated to be 753 μ B and 814 μ B , for route 1 and 2, respectively. Ordered fct Fe-Pt alloys show high values of coercivities of 10,000 Oe and 10,792 Oe for route-1 and route-2, respectively. Observed magnetic properties of the fct Fe-Pt alloys nps were interpreted with the basis of order parameters, size, surface, and composition effects. [ABSTRACT FROM AUTHOR]

Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn 2 type, space group P 6 3 /mmc , with lattice parameters a =536.4 pm, c =845.3 pm. Shortest inter-uranium distance 313 pm (along the c- axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10 −8 m 3 mol −1 (at T =2 K), which is slightly higher with magnetic field along the a- axis compared to the c- axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ =36 mJ mol −1 K −2 . [ABSTRACT FROM AUTHOR]

This work reports the synthesis of Mg x Mn 1−x Fe 2 O 4 (x=0–1) nanoparticles by both sol-gel and thermal decomposition methods. In order to determine the effect of synthesis conditions on the crystal structure and magnetic properties of the ferrites, the synthesis was carried out varying some parameters, including composition. By both methods it was possible to obtain ferrites having a single crystalline phase with cubic inverse spinel structure and a behavior near to that of superparamagnetic materials. Saturation magnetization values were higher for materials synthesized by sol-gel. Furthermore, in both cases particles have a spherical-like morphology and nanometric sizes (11–15 nm). Therefore, these materials can be used as thermoseeds for the treatment of cancer by magnetic hyperthermia. [ABSTRACT FROM AUTHOR]

Nano-sized manganese ferrite (MnFe 2 O 4 ) particles were prepared using co-precipitation method in two different pH (9 and 11). The structural, morphological, optical and magnetic properties of as-synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis absorption and vibrating sample magnetometer (VSM). The FTIR spectra revealed two strong peaks at about 600 and 400 cm −1 that can be attributed to the vibration mode of octahedral and tetrahedral sites of spinel structure of MnFe 2 O 4 , respectively. The XRD results showed that the nanocrystalline MnFe 2 O 4 has pure cubic spinel crystal structure with average crystallite size of 11 nm. The cation distribution of these nanoparticles was estimated by X-ray analysis data. The blue shift was observed in the band gap when compared with bulk sample which is due to the quantum size effect. The absence of hysteresis for MnFe 2 O 4 nanoparticles indicated the superparamagnetic behaviour, as expected for single domain nanoparticles. The obtained value for saturation magnetization being less than its value of bulk ones and larger pH is due to surface effects. The calculated magnetic particle size was smaller than crystallite size estimated from the XRD results; which indicate the presence of dead layer on particle surface. [ABSTRACT FROM AUTHOR]

Temperature (0.5–300 K) and magnetic field ( H up to 90 kOe) dependences of the magnetization ( M ) of a powder sample of vanadyl phthalocyanine (VOPc) having the Phase II-triclinic structure are measured and analyzed. The data of χ = M/H vs. T measured in H = 1 kOe fit the modified Curie-Weiss (CW) law, χ = χ o + C /( T − θ ), with C = 6.266×10 −4 emuK/gOe, θ = −0.1 K and χ o = −9.3×10 −7 emu/gOe. The Curie constant C yields magnetic moment μ = 1.704 μ B , S = 1/2, and g = 1.967 characteristic of VO 2+ . The magnitude of θ = −0.1 K signifying very weak inter-ion antiferromagnetic exchange coupling is supported by the analysis of the variable frequency (9.8–336 GHz) electron paramagnetic resonance data. The isothermal data of M vs. H at ten temperatures between 0.5 K and 300 K when plotted as M vs. H /( T +0.1) collapses on to a single curve given by M = M o tanh { gμ B H /[2k B ( T +0.1)]} with M o = N gμ B S = 9.48 emu/g expected for S = 1/2 system, thus signifying near perfect paramagnetism in VOPc. [ABSTRACT FROM AUTHOR]

Magnetic measurements on variously hydrated nickel chlorides and bromides, including deuterated forms, are reported. Results include locations and sizes of susceptibility maxima, T max and χ max , ordering temperatures T c , Curie constants and Weiss theta in the paramagnetic regime, and primary and secondary exchange interactions from analysis of low temperature data. For the latter a 2D Heisenberg model augmented by interlayer exchange in a mean-field approximation is applied. Magnetization data to 16 kG as a function of temperature show curvature and hysteresis characteristics quite system dependent. For four materials high field magnetization data to 70 kG at 2.00 K are also obtained. Comparison is made with theoretical relations for spin-1 models. Trends are apparent, primarily that T max of each bromide hydrate is less than for the corresponding chloride, and that for a given halide n D 2 O ( n =1 or 2) deuterates exhibit lesser T max than do nH 2 O hydrates. A monoclinic unit cell determined from powder X-ray diffraction data on NiBr 2 ·2D 2 O is different from and slightly larger than that of NiBr 2 ·2H 2 O. This provides some rationale for the difference in magnetic properties between these. [ABSTRACT FROM AUTHOR]

This article reviews magnetic memory effects in spin-glasses (SG), superspin-glasses (SSG) and superparamagnetic (SPM) materials with detailed discussions about protocols and mechanisms. The origin of time (t) and temperature (T) dependent magnetic memory effects in different classes of materials have been discussed starting from the nanoscale towards the bulk magnetism. Magnetic memory effects (T and t dependent) in field cooled (FC) and zero field cooled (ZFC) protocols are focused to understand the physics of ageing and rejuvenation in SG, SSG and SPM materials. The article is enlightened with significant discussion to understand the diverse nature and classified properties of magnetic memory of the said materials. • M emory effects in SG (both in bulk and nano) and SPM materials. • Origin, footprint and diverse characteristics of memory effect. • Significantly covers the field of magnetism especially magnetic metastabilities. • Diverse nature and classified properties of magnetic memory. [ABSTRACT FROM AUTHOR]