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Pure semi-ionic F-doped graphene with the s-F concentration high up to 17.4 at.% (s-FG-17.4) and covalent F-doped graphene with the c-F concentration of 17.8 at.% (c-FG-17.8) were synthesized by fluorination of graphene respectively at the low temperature of 100 °C and the conventional temperature of 200 °C. The electronic and magnetic properties of the two samples were studied. The results show that s-FG-17.4 is metal and exhibits strong ferromagnetism with the Curie temperature of 229 K and high magnetization of 1.1 emu/g; by contrast, c-FG-17.8 is semiconductor and exhibits spin-half paramagnetism with low magnetization of 0.1 emu/g. Thus, this study provided a reliable method to synthesize high-concentration pure s-FG and proposed an effective sp 3 dopants for obtaining metallic and ferromagnetic graphene with high magnetization. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The rhombohedral perovskite LaAl 0.5 Ni 0.5 O 3 (or La 2 AlNiO 6), synthesized by a combustion method is found to contain Al3+ and Ni3+ cations in the rhombohedral lattice. The material exhibits a temperature dependent (thermally excited) paramagnetic susceptibility and follows the modified Curie-Weiss law implying an antiferromagnetic ordering at very low temperatures. A non-saturating hysteresis loop with a coercivity of 108 Oe is observed at 2 K which is arising from the magnetic contribution from Ni in the lattice. The conduction mechanism in LaAl 0.5 Ni 0.5 O 3 for 80–300 K follows the Mott's variable range hopping mechanism. A negative magnetoresistance of 1.75% is observed at 2 K under 90 kOe field which decreases linearly by increasing the temperature up to 18 K and then changes to positive with comparatively low value. Both the negative and positive magnetoresistance increases linearly with an applied magnetic field. Highlights • The rhombohedral perovskite LaAl 0.5 Ni 0.5 O 3 with Al3+ and Ni3+ cations at the B-site is synthesized by a combustion method. • A temperature dependent (thermally excited) paramagnetic susceptibility is observed that follows the modified Curie-Weiss law. • The conduction mechanism follows the Mott's variable range hopping mechanism. • A negative magnetoresistance of 1.75% is observed at 2 K under 90 kOe field. [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]

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]

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]

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature T B of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of T B occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces T B further down to 35 K. Additionally, a second blocked magnetic phase with much higher T B emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix. • Co-rich clusters in nanoporous Pd matrix prepared by electrochemical dealloying. • Co-rich clusters show superparamagnetic behavior. • Annealing leads to diffusion of Co in matrix and shrinkage of magnetic cluster size. • Larger magnetic entities can form at increased annealing temperature of 773 K. • Formation of weakly ferromagnetic Co–Pd alloy phase upon annealing at 973 K. [ABSTRACT FROM AUTHOR]

The graphene system is actively pursued in spintronics for its nontrivial sp electron magnetism and its potential for the flexible surface chemical tuning of magnetoelectronic functionality. The magnetoresistance (MR) of graphene can be effectively tuned under high magnetic fields at cryogenic temperatures, but it remains a challenge to achieve sensitive magnetoelectric response under ambient conditions. We report the use of surface modulation to realize superparamagnetism in reduced graphene oxide (rGO) with sensitive magnetic field response. The superparamagnetic rGO was obtained by a mild oxidation process to partially remove the thiol groups covalently bound to the carbon framework, which brings about large low-field negative MR at room temperature (−8.6 %, 500 Oe, 300 K). This strategy provides a new approach for optimizing the intrinsic magnetoelectric properties of two-dimensional materials. [ABSTRACT FROM AUTHOR]

• The Pb vacancies, O defects and Co ions induce room FM for PbPd 1-x Co x O 2. • F dopant can induce the changed valence states of O, Co and Pd ions. • The enhanced magnetization results mainly from Pd(2−δ)+ and more O1− induced by F. • A magnetization jump at 265 K is observed originate from valence state transformation between O1− and O2−. In this work, Co-doped and Co-F co-doped PbPdO 2 nanoparticles with a body-centered orthorhombic structure were synthesized via sol–gel method. The measured results reveal that, Pb and O vacancies exist in all samples; the valence state of magnetic atom Co is identified as mixed Co2+ and Co3+; all samples exhibit both ferromagnetism and paramagnetism; the incorporation of fluorine results in an evident increase in the magnetic moment of PbPd 0.875 Co 0.125 O 2 @F; a jump of magnetization at about 265 K can be found in both FC and ZFC curves of PbPd 1-x Co x O 2 (x = 0, 0.05, 0.10 and 0.115). Moreover, the origin of the magnetism can be considered as follows: the ferromagnetism for PbPd 1-x Co x O 2 (0 < x ≤ 0.15) results from the combined effect of O1− and magnetic Co ions; fluorine substitution in an oxygen lattice site and the fluorine doping in the interstitial sites can induce both distinct roles on the valence of oxygen, Co and Pd ions, which changes evidently the magnetic properties of PbPd 1-x Co x O 2. Fortunately, the magnetic properties of PbPdO 2 , Co-doped PbPdO 2 , Co-F co-doped PbPdO 2 can be verified by first-principles calculations. It is found that the enhanced magnetization results mainly from Pd(2−δ)+ and more O1− induced by F. Finally, the magnetization jump at about 265 K has been explained by the temperature-dependent valence transformation between O2− and O1−. [ABSTRACT FROM AUTHOR]

The external controllability of the magnetic properties in topological insulators would be important both for fundamental and practical interests. Here we predict the electric-field control of ferromagnetism in a thin film of insulating magnetic topological insulators. The decrease of band inversion by the application of electric fields results in a reduction of magnetic susceptibility, and hence in the modification of magnetism. Remarkably, the electric field could even induce the magnetic quantum phase transition from ferromagnetism to paramagnetism. We further propose a transistor device in which the dissipationless charge transport of chiral edge states is controlled by an electric field. In particular, the field-controlled ferromagnetism in a magnetic topological insulator can be used for voltage based writing of magnetic random access memories in magnetic tunnel junctions. The simultaneous electrical control of magnetic order and chiral edge transport in such devices may lead to electronic and spintronic applications for topological insulators. [ABSTRACT FROM AUTHOR]

We report on the structural evolution and the magnetic properties of a CaNix-1MnxGe system that combines a Pauli paramagnetic matrix CaNiGe with a magnetic substituent Mn. The results indicate that the system crystallizes into a single-phase CeFeSi-type structure for x ≤ 0.1 and x ≥ 0.95. For 0.05 ≤ x ≤ 0.1, DC an AC magnetization measurements confirm that the system undergoes a ferromagnetic ordering at around 130 K followed by a magnetic glass transition at the susceptibility maximum near 80 K. AC measurements for the sample x = 0.05 reveal a frequency (v) dependence factor Δ Tf/[Tf(Δ logv)] of 0.006 and a field dependence of Tf = α + bH1.28 for the glass-transition temperature Tf. The observed spin-glass-like magnetic behavior for this dilute magnetic system of Mn-doped CaNiGe is interpreted in terms of the coexistence of the magnetic glass state and ferromagnetic clusters. [ABSTRACT FROM AUTHOR]

Abstract: We developed a simple synthesis method for production of CoFe2O4 nanoparticles. The method is based on the solid state ball-milling and calcinations of acetate precursors and citric acid. The samples were characterized using X-ray diffraction, transmission electron microscope, Fourier transform infrared and energy-dispersive X-ray spectroscopy. Magnetic properties of the samples were studied using vibrating sample magnetometer and ac susceptibility measurements. The results show that the products mainly consist of CoFe2O4 nanoparticles. Magnetization measurements demonstrate the effect of calcination temperature on particle size and hence, on the magnetic properties of the CoFe2O4 nanoparticles. By increasing the particle size from 3.5 to 7.2nm, the room temperature coercivity and magnetization increase from 0 to 152Oe and from 8 to 30emu/g respectively. Also, the low temperature calcinated samples, C250 and C30 are superparamagnetic in nature due to it’s near-zero coercivity and remanence. We estimated the mean value of the effective anisotropy constant, K eff =9.2×106 erg/cm3. This value is much larger than the bulk value, due to the surface effects. [Copyright &y& Elsevier]

We present systematic studies of the magnetocaloric properties of the polycrystalline La1− x Ca x MnO3 system for x = 0.3, 0.35, and 0.4 near a second-order phase transition from a ferromagnetic to a paramagnetic state. The crystal structure of the studied manganites was shown to be in good agreement with previous reports. The value of the magnetocaloric effect has been determined from the measurement of magnetization as a function of temperature and external magnetic field. The maximum entropy change detected in La0.7Ca0.3MnO3 at a field of 2 T reaches 8 J/kg K which exceeds that of gadolinium. In all studied samples, the paramagnetic–ferromagnetic transition is very narrow but no hysteresis is observed and the transitions are identified as second-order ones. The phase transition in La0.7Ca0.3MnO3 appears to be almost of first-order. [ABSTRACT FROM AUTHOR]

Abstract: Magnetite particles of 2–4 nm were synthesized by an economic, biocompatible chemical coprecipitation route, with their size tuned by the reaction temperature. The microstructure and morphology of the nanoparticles were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), whereas the magnetic properties were investigated by vibrating sample magnetometry (VSM) and superconducting quantum interference device (SQUID). It is found that the nanoparticles demonstrate well-defined superparamagnetic behavior as prepared and after annealing. Distinct lattices were observed which manifest the high crystallinity of such ultrasmall particles and the finite-size effect was revealed by analyzing the corresponding microstructure and magnetism. [Copyright &y& Elsevier]

Nanoscale maghemite samples were obtained by a solid-state displacement reaction activated by mechanochemical treatment for two different milling times, 30min (sample S1) and 4h (sample S2). Samples were characterized by X-ray powder diffraction, transmission electron microscopy and SQUID magnetometry. The results show that prolongation of the milling time increases particle size while reducing the crystallinity, with a strong impact on the magnetic properties. Coercivity of 3.3kOe at 5K temperature for S2 is among the highest values reported so far for the maghemite nanoparticles. [Copyright &y& Elsevier]

Abstract: Static and dynamic magnetic properties are examined for granular systems Co x (TiO2)1− x with Co volumetric contents of 31.6, 41.4, 49.4 and 57.6vol%. The ferromagnetic resonance (FMR) technique in the 38–45GHz band and the vibrating sample magnetometer technique were applied. The results from comparative analysis of saturation magnetization defined by both methods are discussed and the estimation of the most probable sizes and shapes of magnetic particles forming the nanocomposite is carried out. [Copyright &y& Elsevier]

Nanocrystalline nickel–zinc, zinc–manganese, and nickel–manganese ferrites synthesized by reverse micelle synthesis technique were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, and the magnetic behavior studied by Superconducting Quantum Interference Device. The mixed (Ni–Zn, Zn–Mn, and Ni–Mn) ferrites exhibit blocking temperatures of 11, 20, and 15 K, respectively. The small differences in the blocking temperatures are attributed to the magnetocrystalline anisotropy and L–S coupling. The saturation magnetization of nanocrystalline Ni–Zn, Zn–Mn, and Ni–Mn at 300 K was 4.5, 9, and 7 emu/g, respectively, and at 2 K was 15, 19, and 14 emu/g, respectively. The lower saturation magnetization of the nanocrystalline ferrites compared to their bulk counterparts is attributed to the core–shell morphology of the particles consisting of ferromagnetically aligned core spins and a spin-glass-like surface layer. [Copyright &y& Elsevier]

A section adjacent to a building structure at She¨n De¨li, Butrint, Southern Albania exposes what is believed to be the remains of a former Roman bath-house. This section shows a transition from the underlying natural marsh clay into an archaeological deposit, which is both the basal remains of a building structure, and what appears to be an ash and charcoal enriched midden. The micro and macrocharcoal, magnetic and physical properties indicate a number of phases in the archaeological deposits, culminating in the micro and macrocharcoal rich and magnetically enhanced midden. The magnetic properties of these deposits are strongly related to the charcoal content that is probably a reflection of the ash content. The midden deposit is strongly enhanced in both superparamagnetic and low coercivity magnetite. The charcoal content and magnetic properties of the midden indicate a high content of wood-ash produced at the bath-house site, which is consistent with the anticipated fuel source for the region in Roman times. [Copyright &y& Elsevier]

To evaluate paramagnetic fluctuations and their contribution to entropy change of magnetic phase transition, paramagnetic susceptibility of La(Fe0.88Si0.12) was investigated after modifying the magnetic state by application of pressure or by the partial substitution of Ce or Al. Volume reduction by hydrostatic pressure or partial substitution of Ce maintains the value of effective moment peff, and comparison of peff with spontaneous moment at ground state suggests the appearance of disordered local moment in the paramagnetic phase. Reduction of the paramagnetic Curie temperature θp by these modifications is faster than that of the Curie temperature TC. Change in the difference TC -θP is equivalent to that in the entropy change ΔSCC obtained from the Clausius-Clapeyron relation. On the contrary, partial substitution of Al brings about an increase of itinerant character, accompanying a reduction of ΔSCC. [ABSTRACT FROM AUTHOR]

The authors have investigated the structural and magnetic properties of CrN films grown on MgO(001) and sapphire(0001) by rf-plasma-assisted molecular beam epitaxy. CrN/MgO(001) exhibits a better epitaxial quality than CrN/sapphire(0001). The CrN/MgO film shows clear paramagnetic behavior at low temperatures, whereas CrN/sapphire exhibits a ferromagneticlike response with an order temperature above room temperature which resembles the magnetic behavior found in Cr-doped dilute magnetic semiconductors. Keeping in mind that bulk CrN exhibits antiferromagnetic behavior, the dramatically different magnetic behaviors found in epitaxial CrN films grown on MgO and sapphire demonstrate the importance of epitaxial constraints in determining their magnetic properties. [ABSTRACT FROM AUTHOR]

Well-defined CoFe2 O4 nanoparticles embedded in an amorphous SiO2 matrix have been synthesized by a sol-gel method, characterized and investigated by Mössbauer spectroscopy and magnetic properties measurements. The mean particle size increases from 3 to 15 nm consistently with the temperature of the subsequent annealing, which varied from 800°C to 1100°C, respectively. The composites exhibit superparamagnetic behavior with the blocking temperature TB increasing with the mean particle size from 80 to 350 K, respectively. Sufficiently high value of Hc ∼ 2.5 T (at 2 K) has been observed for the sample annealed at 1100°C. [ABSTRACT FROM AUTHOR]

We report on the magnetic properties of CuO nanoparticles prepared by the sol-gel method. M (T) curves show a blocking temperature at TB = 135 K and 160 K for 13 nm and 17 nm size particles, respectively, in measuring field H = 100 Oe. The M-H data for both the samples show a reversal magnetization at 300 K, whereas below TB it exhibit symmetrical hysteresis loops with a coercive field of 200 Oe (155 Oe) and a remanence 0.306 emu/mole (0.171 emu/mole) for 13 nm (17 nm) at 5 K. Presence of superparamagnetism and net magnetic moments of CuO nanoparticles are attributed to the uncompensated Cu2+ ions at the surface of the particles. [ABSTRACT FROM AUTHOR]

Superparamagnetic regions and magnetic anisotropic properties in randomly orientated Co nanodots (NDs) are investigated as a function of dot diameter. The Co NDs are fabricated by intentionally exposing a laser source on ultrathin Co film. Various dot sizes are ultimately realized by changing laser power, scan condition, and initial film thickness. Magnetic hysteresis loops and temperature dependence magnetization of the Co NDs are measured with a superconducting quantum interference device. The analysis of magnetization and hysteresis loops is effectively used to determine superparamagnetic regions of the Co NDs. The experimentally observed results repealed that room temperature superparamagnetic limit of our Co NDs was about 30 nm in diameter, with the confirmation of high resolution transmission electron microscope. [ABSTRACT FROM AUTHOR]

Abstract: We report on the rare-earth valence and paramagnetic properties of Ce1− z Yb z Fe4Sb12, Ba y Fe4Sb12 and La y Fe4Sb12. Yb valence decreases from 2.7 for for whereas Ce is always trivalent. The dominant character of the magnetic interaction changes from ferromagnetic with divalent filler to antiferromagnetic with trivalent filler. The paramagnetic properties are dominated by the delocalized electrons of [Fe4Sb12] with a constant contribution close to 3.2μ B (f.u.)−1. [Copyright &y& Elsevier]

The magnetic properties and clustering behaviors of the transition-metal (TM)-doped ZnO have been studied by first-principles calculations. We demonstrate the relationship between the types of TM (Co, Fe, Ni, and Cu) pairs and the energetic most stable configurations in ZnO:TM. Further calculations show that Co pairs have no tendency to form clusters, showing paramagnetic (PM) state in ZnO:Co samples in an equilibrium state and without excessive defects, as evidenced by various experiments, while ferromagnetic (FM) state is possible for the samples prepared under non-equilibrium conditions. Finally, systematical studies of a series of TM elements reveal different types of TM pairs in terms of clustering behaviors determined by spin-polarized and non-spin-polarized contributions: Co pairs and Fe pairs have no tendency to form clusters, showing PM and FM states, respectively, while Ni pairs and Cu pairs have a clustering tendency and show intrinsic FM ordering. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic properties of surfactant-coated and uncoated superparamagnetic iron oxide nanoparticles, Fe3O4 (SPION) were investigated by electron spin resonance (ESR) technique. For all samples, a strong and broad single ESR signal has been observed at all temperatures. A strong temperature dependence of ESR linewidth and resonance field is observed. Also, there is a strong effect of surfactant coating on magnetic properties of Fe3O4 nanoparticles. While the resonance field is decreasing by coating, the linewidth of the ESR spectra is increasing. These changes in resonance field and the linewidth are attributed to the decrease in effective magnetic moment due to a non-collinear spin structure originated from the pinning of the surface spins and coated surfactant at the interface of nanoparticles. Also, the changes are due to the contribution of the volume of the diamagnetic coating mass to the sample volume. [Copyright &y& Elsevier]

Abstract: Using a co-precipitation method, perovskite-type manganese oxide La0.7Sr0.3MnO3 nanoparticles (NPs) with particle size 12nm were prepared. Detailed studies of both 55Mn nuclear magnetic resonance and superparamagnetic resonance spectrum, completed by magnetic measurements, have been performed to obtain microscopic information on the local magnetic structure of the NP. Our results on nuclear dynamics provide direct evidence of formation of a magnetically dead layer, of the thickness ≈2nm, at the particle surface. Temperature dependences of the magnetic resonance spectra have been measured to obtain information about complex magnetic properties of La0.7Sr0.3MnO3 fine-particle ensembles. In particular, electron paramagnetic resonance spectrum at 300K shows a relatively narrow sharp line, but as the temperature decreases to 5K, the apparent resonance field decreases and the line width considerably increases. The low-temperature blocking of the NPs magnetic moments has been clearly observed in the electron paramagnetic resonances. The blocking temperature depends on the measuring frequency and for the ensemble of 12nm NPs at 9.244GHz has been evaluated as 110K. [Copyright &y& Elsevier]