Search

Despite being difficult to identify, extremely dilute oxygen vacancies have been widely reported to play an important role in enhancing magnetism in ZnFe 2 O 4. The mechanisms underlying this enhanced magnetism have not been well understood for a long time and remain controversial because the formation of oxygen vacancy-rich ZnFe 2 O 4 can be accompanied by changes in the chemical/physical characteristics, especially the composition, particle size, surface morphology and cation distribution, which can significantly affect the magnetization. An open and important question is whether and to what extent the enhanced magnetization can be attributed only to oxygen vacancies. In this study, the relationship between the magnetization and oxygen vacancies in ZnFe 2 O 4 was definitively determined by using a carefully designed "shake-and-heat" treatment to prepare vacancy-rich samples while keeping the other crystal/surface parameters constant. Compared to the nearly vacancy-free paramagnetism samples, the vacancy-rich samples exhibited a higher magnetization of approximately 5 emu/g at both 300 K and 2 K. The Fe3+-O2--Fe3+ superexchange paths broken by oxygen vacancies then resulting in the Fe3+-Fe3+ ferromagnetism configuration. Meanwhile, the oxygen vacancy is highly diluted then the ferromagnetism configuration is confined in a single super-cell, favoring a short-range magnetic ordering at room temperature. The concentration of oxygen vacancies was calculated to be 0.68% by magnetization measurement. Our results may shed a light on how oxygen vacancies affect magnetism. [ABSTRACT FROM AUTHOR]

Bi 25 FeO 39 microcrystals were synthesized via a one-pot hydrothermal process without additives, where their hierarchical structures could be designed from tetrahedron to orchid and marigold by the increment of pH values and reaction time. For all types of as-prepared Bi 25 FeO 39 , a high crystallinity and purity was confirmed in XRD and XPS analysis. A good thermal stability up to 1000 °C was revealed by DSC-TG with two endothermal peaks corresponding to decompositing and melting. A magnetic transition between ferromagnetism and paramagnetism around 36.3 K was distinguished from thermomagnetic curves as well as hysteresis loops at 5 K and 300 K respectively. In contrast to tetrahedron and orchid shaped Bi 25 FeO 39 , marigold shaped Bi 25 FeO 39 exhibited a higher magnetization up to 4.8 emu/g at 5 K and enhanced photocurrent density around 0.37 μA/cm2. The special crystal arrays and increased concentration of Fe should be responsible for it. This work paves an attractive way for facile preparation and potential applications of sillenite materials. [ABSTRACT FROM AUTHOR]

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]

Both theoretical calculations and experiments indicate that a monolayer CoSb/SrTiO 3 film has high-temperature superconductivity resembling the case of FeSe/SrTiO 3. However, no superconductivity was found in the bulk CoSb, even under high pressure. Moreover, the magnetic properties of CoSb have always been controversial. Here, we have studied the electrical property, magnetic property, and X-ray photoelectron spectroscopy (XPS) of CoSb single crystals. Electrical and magnetic transportation measurements reveal that CoSb is a Pauli paramagnetic metal with non-Fermi liquid behavior. The XPS results showed that both Co and Sb in CoSb are in the zero-valence state, and they form an alloy in which the metallic bond is dominant. The Pauli paramagnetism of CoSb originates from its itinerant electrons. Therefore, unveiling the electronic states of CoSb single crystal not only help us understand its magnetic properties, but would also pave the way for searching for the possible high-temperature superconductivity. • CoSb single crystals with large size were synthesized. • CoSb is a Pauli paramagnetic metal with non-Fermi liquid behavior. • XPS analysis indicates that both Co and Sb are in the zero-valence state in CoSb. • The Pauli paramagnetism of CoSb originates from its high-density itinerant electrons. [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]

The origin of magnetism in RF magnetron sputtered deposited carbon thin films is reported. Three different carbon thin films were deposited using RF magnetron sputtering of carbon target by Ar ions at RF power of 50 W, 100 W and 150 W, respectively. Microstructural characterization of films using Raman spectroscopy confirms the presence of graphitic crystallites in all three films and the crystallite edges are terminated with the sp3 bonding. However, increasing RF power results in an increase in graphitic crystallite size as well as the sp2/sp3 hybridization ratio, while the average density of the films decreases. The observed magnetization (measured using SQUID-VSM) in all the three-carbon films has a contribution from both superparamagnetic (SPM) particles (due to the interaction between unpaired spins) and the paramagnetic term due to isolated unpaired spins distributed throughout the film. The origin of experimentally observed magnetization in the carbon thin films and their correlation with the change in density and sp2/sp3 hybridization ratio due to variation in RF power is discussed. Image 1 [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]

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]

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]

Using an efficient first-principles computational scheme, we calculate the intrinsic stacking fault energy ( γ i s f ) and the unstable stacking fault energy ( γ u s f ) of paramagnetic γ -Fe as a function of temperature. The formation energies are derived from free energies accounting for thermal longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the accurate description of the temperature-dependent magnetism, intrinsic and unstable stacking fault energies, and have a comparatively large effect on γ i s f of γ -Fe. Dominated by the magneto-volume coupling at thermal excitations, γ i s f of γ -Fe exhibits a positive correlation with temperature, while γ u s f declines with increasing temperature. The predicted stacking fault energy of γ -Fe is negative at static condition, crosses zero around 540 K, and reaches 71.0 mJ m −2  at 1373 K, which is in good agreement with the experimental value. According to the plasticity theory formulated in terms of the intrinsic and unstable stacking fault energies, twinning remains a possible deformation mode even at elevated temperatures. Both the large positive temperature slope of γ i s f and the predicted high-temperature twinning are observed in the case of austenitic stainless steels. [ABSTRACT FROM AUTHOR]

A series of paramagnetic ionic liquids (PILs) based on N , N ′-bis(alkyl)imidazolium bromotrichloroferrate(III), [(C n ) 2 Im][FeCl 3 Br] (Im = imidazole; C n  = ethyl, butyl, hexyl, octyl, decyl, dodecyl), was prepared and compared against the more traditional [C n C 1 Im][FeCl 3 Br] (C 1  = methyl) analogs. Both series were extensively characterized by physical, chemical, and computational methods including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), spectroscopy (FTIR and UV‐vis-NIR), magnetic susceptibility, surface tensiometry, density, and viscosity. The X-ray crystal structure of [(C 12 ) 2 Im][FeCl 3 Br] was also obtained. Notably, all ionic liquids prepared in this study show short-term thermal stabilities exceeding 300 °C in air and have melting points equal to or lower than 25 °C, which is surprisingly low for ionic liquids containing symmetrical cations. In addition, all presented ionic liquids have relatively low viscosities allowing for easier transitioning into applications. Physical property trends are discussed. [ABSTRACT FROM AUTHOR]

Cerium dioxide clearly raises the question of whether spontaneous ferromagnetic order is possible at high temperatures without d- electrons. There are many reports in the literature of a ferromagnetic-like response to an applied magnetic field at room temperature for bulk, nanocrystalline or thin film samples, with or without cation doping. Typical values of the saturation magnetization are very small, of order 0.1 kAm −1 , but reports range from zero up to 1000 kAm −1 . The effect is somehow related to lattice defects – Ce 3 + cations or oxygen vacancies – but it is a challenge to understand how electrons associated with these defects could order ferromagnetically at room temperature and above. Straightforward impurity effects are considered, and models based on conventional ferromagnetic superexchange or double exchange are discussed, as is exchange splitting of the 4 f band or a defect-related impurity band. Results are also compared with a new model of athermal giant orbital paramagnetism that involves no spontaneous ferromagnetic order. A key issue is the fraction, if any, of the volume of the CeO 2 samples that is spontaneously ferromagnetic. Detailed analysis of the magnetic properties suggests that the conventional explanations of the magnetism of CeO 2 are untenable, and directions for further research are suggested. [ABSTRACT FROM AUTHOR]

One-pot reactions of pre-assigned molar ratios of appropriate metal (II) salts and HL 1 (2-acetylpyridine nicotinoylhydrazone) or HL 2 (2-acetylpyridine isonicotinoylhydrazone) in MeOH solutions at room temperature afford 1D coordination polymeric chain [Cu(μ-L 1 ) (Cl)] n ( 1 ) and a mononuclear complex [Ni(L 2 ) 2 ] ( 2 ). The compounds ( 1) and ( 2 ) were characterized using elemental analyses, spectral and other physicochemical methods. Single crystal X-ray diffraction measurements for ( 1 ) and ( 2 ) have been made to define the molecular aggregates and crystalline architectures. In ( 1 ), each copper (II) center adopts a distorted square pyramidal geometry with a CuN 3 OCl chromophore linked through μ-L 1 to form the 1D polymeric chain. While in ( 2 ) each Ni(II) cation is six-coordinate with octahedral structure having NiN 4 O 2 chromophore containing two L 2 units each functioning as a classical tridentate (N,N,O) chelator. Different weak non-covalent interactions promote dimensionalities in the compounds. A Hirshfeld surface analysis was employed to gain additional insight into interactions responsible for packing of ( 1 ) and ( 2 ). Magnetic susceptibility measurement of (1 ) in the 4–300 K range reveals simple paramagnetism. [ABSTRACT FROM AUTHOR]

In this work, a new intercalated FeS compound: (C 2 H 8 N 2 ) 0.4 Fe 2 S 2 was synthesized via the solvothermal route. The product is stable in air and shows the micron-sized plate shape. Structure refinement indicates that (C 2 H 8 N 2 ) 0.4 Fe 2 S 2 adopts the I 4/ m space group with the lattice constants a = 3.6906(6) and c = 20.4215(11) Å. The [FeS] layer crystallizes into the anti-fluorite structure with edge-sharing tetrahedrons and the C 2 H 8 N 2 molecules are inserted in between the layers. (C 2 H 8 N 2 ) 0.4 Fe 2 S 2 is the first intercalated FeS compound reported up to now that contains the electroneutral guest layers. This specific feature leads to the paramagnetic behavior without any magnetic transition in the measured temperature range. Furthermore, we find that the ferromagnetic interaction can also be easily induced in this compound by inserting the extra Fe in between the layers, indicating the controllable magnetism of the title compound. The absence of superconductivity in (C 2 H 8 N 2 ) 0.4 Fe 2 S 2 is mainly due to the external pressure on FeS layers induced by En intercalation. [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]

• 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]

We reported the magnetism, magnetic phase transition behavior and magnetocaloric effect of the ternary Dy 2 CuSi 3 and Ho 2 CuSi 3 compounds. A second order magnetic phase transition from a paramagnetic (PM) to ferromagnetic (FM) state around their respective Curie temperatures were confirmed by using the magnetic measurements and rescaled magnetic entropy change curves in both compounds. A large magnetic entropy change was obtained with the absence of thermal and magnetic hysteresis loss in both compounds. The maximal magnetic entropy change (-Δ S M max ) reach 18.3 and 28.3 J/kg K for a magnetic field change of 0–70 kOe in Dy 2 CuSi 3 and Ho 2 CuSi 3 , respectively. The corresponding values of relative cooling power ( RCP ) are evaluated to be 460 J/kg and 627 J/kg, respectively. [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]

First-principles calculations have been performed to study the effect of C on the stacking fault energy (SFE) of paramagnetic γ -Fe and Fe Cr Ni austenitic steel. In these systems, the local magnetic structure is very sensitive to the volume in both fcc and hcp structures, which emphasizes the importance of the magnetovolume coupling effect on the SFE. The presence of C atom suppresses the local magnetic moments of Fe atoms in the first coordination shell of C. Compared to the hypothetical nonmagnetic case, paramagnetism significantly reduces the effect of C on the SFE. In the scenario of C being depleted from the stacking fault structure or twin boundaries, e.g. , due to elevated temperature, where the chemical effect of C is dissipated, we calculate the C-induced volume expansion effect on the SFE. The volume induced change in the SFE corresponds to more than ∼ 50% of the total C effect on the SFE obtained assuming uniform C distribution. [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]

In this paper, we derive a new force–extension formula for stretched macromolecules and homogeneous polymer matrices. The Ising model arising from paramagnetism is employed, where the magnetic force is replaced by the external force, and the resistance energy is addressed in this model instead of the usual persistent length arising from the freely jointed chain and worm-like chain models. While the force–extension formula reveals the distinctive stretching features for stretched polymers, the resistance energy is found to increase almost linearly with the external force for our two polysaccharides stretching examples with and without ring conformational changes. In particular, a jump in the resistance energy which is caused by a conformational transition is investigated, and the gap between the jump determines the energy barrier between two conformational configurations. Our theoretical model matches well with experimental results undergoing no and single conformational transitions, and a Monte Carlo simulation has also been performed to ensure the correctness of the resistance energy. This technique might also be employed to determine the binding energy from other causes during molecular stretching and provide vital information for further theoretical investigations. [ABSTRACT FROM AUTHOR]

The magnetic forces between paramagnetic squares cannot be calculated using a classic dipolar model because the magnetic field distribution is not uniform within square particles. Here, we present the calculation of magnetic forces and torques on paramagnetic squares in a uniform 2-D magnetic field using a Laplace's equation solver. With these calculations, we simulate the variations in equilibrium configurations as a function of number of interacting squares. For example, a single square orients with its diagonal directed to the external field while a system of multiple squares will assemble into chain-like structures with their edges directed to the external field. Unlike chains of spherical magnetic particles, that easily stagger themselves to aggregate, chains consisting of magnetic squares are unable to aggregate due to interchain repulsion. [ABSTRACT FROM AUTHOR]

The precipitation-hardenable nickel–chromium-based superalloy X-750 exhibits excellent mechanical properties at high-to-cryogenic temperatures. However, little is known about its other properties, even though it is used in a wide range of applications. To elucidate the additional properties of X-750, we studied the effects of its nanostructural evolution on both its mechanical and magnetic properties. We found that precipitation not only mechanically hardens this superalloy, but also induces soft magnetism as well as notable magnetic losses at ultralow temperatures. This information should aid the design of superconducting instruments based on the X-750 superalloy as a structural material. [ABSTRACT FROM AUTHOR]

The precise quantification of catalyst residues in purified carbon nanotubes is often a major issue in view of any fundamental and/or applicative studies. More importantly, since the best CNTs are successfully grown with magnetic catalysts, their quantification becomes strictly necessary to better understand intrinsic properties of CNT. For these reasons, we have deeply analyzed the catalyst content remained in nickel–yttrium arc-discharge single walled carbon nanotubes purified by both a chlorine-gas phase and a standard acid-based treatment. The study focuses on Ni analysis which has been investigated by transmission electron microscopy, X-ray diffraction, thermogravimetry analysis, and magnetic measurements. In the case of the acid-based treatment, all quantifications result in a decrease of the nanocrystallized Ni by a factor of two. In the case of the halogen gas treatment, analysis and quantification of Ni content is less straightforward: a huge difference appears between X-ray diffraction and thermogravimetry results. Thanks to magnetic measurements, this disagreement is explained by the presence of Ni 2+ ions, belonging to NiCl 2 formed during the Cl-based purification process. In particular, NiCl 2 compound appears under different magnetic/crystalline phases: paramagnetic or diamagnetic, or well intercalated in between carbon sheets with an ordered magnetic phase at low temperature. [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]

In situ X-ray photo-emission electron microscopy is used to investigate the magnetic properties of iron nanoparticles deposited on different single crystalline substrates, including Si(001), Cu(001), W(110), and NiO(001). We find that, in our room temperature experiments, Fe nanoparticles deposited on Si(001) and Cu(001) show both superparamagnetic and magnetically stable (blocked) ferromagnetic states, while Fe nanoparticles deposited on W(110) and NiO(001) show only superparamagnetic behaviour. The dependence of the magnetic behaviour of the Fe nanoparticles on the contact surface is ascribed to the different interfacial bonding energies, higher for W and NiO, and to a possible relaxation of point defects within the core of the nanoparticles on these substrates, that have been suggested to stabilise the ferromagnetic state at room temperature when deposited on more inert surfaces such as Si and Cu. [ABSTRACT FROM AUTHOR]

Magnetism been studied in two series of nanocrystalline SiC films obtained by the method of direct deposition of ions with an energy of ~100 eV at temperatures 1150 °С and 1200 °С. There were separated the contributions of diamagnetism, paramagnetism and superparamagnetism+ferromagnetism. Magnetization value of the films correlates with the deposition temperature. In the films deposited at higher temperatures the value of magnetization was by 1.5 times lower. It was concluded that induced magnetism in nanocrystalline SiC films is caused by interaction of magnetic moments of neutral V Si V C divacancies in separate nanocrystals. The estimated concentration of neutral V Si V C divacancies in nanocrystalline SiC films is ~10 20 сm −3 . [ABSTRACT FROM AUTHOR]

Magnetic properties and magnetocaloric effect (MCE) in ErFeAl and HoFeAl intermetallic compounds have been studied systematically. Both compounds undergo a second order magnetic phase transition from paramagnetic to ferromagnetic state together with a probable spin reorientation transition at low temperature. A considerable reversible magnetocaloric effect was observed around its own Curie temperatures T C ∼55 K and 80 K for ErFeAl and HoFeAl, respectively. For a magnetic field change of 0–7 T, the maximum values of magnetic entropy change (−Δ S M max ) are found to be 8.3 and 9.9 J/kg K for RE = Er and Ho, respectively. The corresponding values of refrigerant capacity ( RC ) are evaluated to be 384 and 647 J/kg. [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 so-called “metal-radical approach” to the design of molecule-based magnetic materials relies on the availability of paramagnetic ligands that can reliably form coordination complexes with paramagnetic metal ions. While the most common radical ligands are based on nitroxides, other paramagnetic building blocks are also gaining attention. Thiazyls and their related selenazyls are promising candidates for the development of radical ligands and, because they have inherently interesting materials’ properties, their use as ligands has the potential to generate novel materials with unprecedented properties. Significant progress has been made in this field in the past ten years. This review is a timely look back at the development of the field, highlighting the diversity of complexes and designs, and a look forward to a promising future. [ABSTRACT FROM AUTHOR]

We report on the magnetic property of 0.67–WO 3 +0.33–VO x mixture film deposit on the corning glass substrate using the chemical sol–gel and atmospheric pressure chemical vapor deposition (APCVD) methods. The XRD and Raman spectroscopy confirm species of both materials, and the morphological studies with FIB-SEM and TEM reveal segregation of W and V atoms. XPS reveals that V 4+ from VO 2 forms only 11% of the film; V 3+ in the form of V 2 O 3 form 1% of the film, 21% is V 5+ from V 2 O 5 and 67% is given to W 6+ from WO 3 . The analysis of the ESR data shows some sharp changes in the magnetism near the metal-to-insulator (MIT), which could be theoretically interpreted as the ordering or alignment of electron spins from net moment nature to parallel alignment of magnetic moment. The derivatives of magnetic susceptibility established the thermally induced magnetic property: two distinct transitions of 339 K for heating data and 338 K for cooling data for 151.2 mT field were obtained. Similar results were also obtained for 308.7 mT field, 336 K for heating data and 335 K for cooling data. VSM results confirm a paramagnetic phase with a small amount of magnetically ordered phase. [ABSTRACT FROM AUTHOR]

In this work we investigate magnetic effects in terms of the translational and rotational invariances of magnetisation. Whilst Landau-type diamagnetism originates from translational invariance, a new diamagnetism could result from rotational invariance. Translational invariance results in only conventional Landau-type diamagnetism, whereas rotational invariance can induce a paramagnetic susceptibility for localised electrons and also a new kind of diamagnetism that is specific to conducting electrons. In solids, the moving electron shows a paramagnetic susceptibility but the surrounding screening of electrons may produce a new diamagnetic response by Lenz's law, resulting in a total susceptibility that tends to zero. For electricity, similar behaviours are obtained. We also derive the DC-type negative electric susceptibility via two methods in analogy with Landau diamagnetism. [ABSTRACT FROM AUTHOR]

The Ni50Mn37AlxSb13-x (x=0, 1, 3 and 5) alloys were prepared by tri-arc melting technique. The replacement of Sb by Al increases the martensitic transformation temperature (TM) as well as ferromagnetic to paramagnetic transformation temperature (=start_CONVERSION_=TCA=start_CONVERSION_=) within the austenite phase. The increase in TM is found to due to the enhancement of hybridization between 3d states of Ni and Mn atoms. We also observed a large exchange bias field (HEB) of 470Oe for x=0 and it decreases with the Al concentration for field cooled (FC) magnetic hysteresis loop. A large magnetic entropy change (ΔSM) of 10J/kg-K is found for x=1 alloy under a field change (ΔH) of 50kOe and it decreased for further higher concentration of Al doping. The possible reasons for observed behaviors are discussed. [ABSTRACT FROM AUTHOR]

Abstract: A correlation between the DC magnetization and hyperthermia heating rate in high frequency magnetic fields was established for two distinctively different magnetic nanoparticle (MNP) systems: (1) polystyrene (PS)/Fe3O4 based composites, consisting of 10nm diameter Fe3O4 nanoparticles embedded in the matrix of polystyrene (PS) spheres (~100nm), and (2) similar Fe3O4 nanoparticles coated with polyacrylic acid (PAA) and dispersed in water. Due to physical confinement of Fe3O4 nanoparticles in the former, the PS/Fe3O4 composite exhibited much lower magnetic hyperthermia heating compared to the latter. The reduced magnetic hyperthermia heating in the polystyrene (PS)/Fe3O4 based composites was found to be associated with strong dipolar interactions. [Copyright &y& Elsevier]

Pressure dependent magnetization and 57Fe Mössbauer studies were performed on Fe(TCNE)[C4(CN)8]1/2·zCH2Cl2 (TCNE=tetracyanoethylene). Pressure did not influence the Mössbauer parameters in paramagnetic state. Mössbauer data reveals the onset of magnetic ordering at 130K and significant enhancement of the magnetic ordering temperature from 100 to 150K accompanied by an increase of the spontaneous magnetization, which is higher than reported from the magnetic data, and application of pressure induces the reversible formation of a new, metastable magnetic species. These changes suggest an increase of the dimensionality of magnetic interaction, i.e., stronger interlayer coupling. Application of 9.3kbar increases T c to 160K, and the moderate dT c/dP of ∼1K/kbar in the pressure-induced metastable state suggests a pressure-induced structural phase transformation that increases the number of next–nearest neighbors of iron. [ABSTRACT FROM AUTHOR]

Abstract: Conventional magnetic order in a material requires the partially filled d or f bands. The exchange interactions between the electrons in these partially filled bands give rise to a magnetic order. However, the discovery of unexpected magnetism observed in some nanomaterials, which have the d and f shells either completely empty or full, has challenged our understanding of magnetism in conventional materials. The magnetism in nanomaterials shows the effects of reduced dimensions, reduced coordination of atoms at the surface and some quantum effects which dominate at low dimensions. In this review paper we give a brief review and discuss the unexpected magnetism experimentally observed and/or theoretically predicted in nanomaterials of conventional magnetic and nonmagnetic bulk materials. [Copyright &y& Elsevier]

Abstract: We have studied the effect of Fe for Mn substitution on magnetic properties of NdMn1−x Fe x O3+δ compounds. Our heat capacity, AC susceptibility and magnetization measurements revealed that the transition from paramagnetic to magnetically ordered state of the Mn sublattice decreases linearly from T N=74.9K to T N=49K with doping up to x=0.25. The ordering temperature T 1 of Nd sublattice varies in a non-monotonous way in the temperature range 11–16K. For x=0.3, the ordering of the Mn/Fe sublattice is residual, while the magnetism in Nd sublattice seems to be intact. The broad maximum in heat capacity C(T) at about 10K was ascribed by 2-level Schottky contribution (Δ=21(1)K) for x=0, but this description failed for Fe-doped samples. An upturn of C(T) at temperatures below 0.5K was observed on NdMnO3 and can be accounted to nuclear contribution. A more detailed study of AC susceptibility performed on samples with x=0.1 and 0.2 revealed a shift of both peaks to higher temperature with increasing frequency. The compensation temperature and a large negative field-cooled magnetization was observed for concentrations x=0.2 and x=0.25. [Copyright &y& Elsevier]

Abstract: Herein we report on pattern formation of a self-assembled monolayer (SAM) using soft colloidal lithography, based on strong physical contact between microspheres and substrate. In typical colloidal lithography, weak contact of microspheres with the substrate does not block the formation of a SAM. To establish conformal contact between microspheres and substrate to block the formation of a SAM, magnetic force was exerted on softened paramagnetic microspheres that had been swollen by a solvent. The soft colloidal lithography with controlled buoyance enables pattern formation through simple wet chemistry. [Copyright &y& Elsevier]

Abstract: Magnetic mesoporous silica (SCF) with cobalt ferrite nanoparticles embedded in silica, exhibiting a mesoporous structure, high magnetic responsivity and paramagnetism, was prepared using a reverse microemulsion-mediated sol–gel method and then modified with 3-mercaptopropyl trimethoxysilane to achieve sulfhydryl-group-modified SCF (MPS-SCF). 1-Allyl-3-(butyl-4-sulfonyl) imidazolium trifluoromethanesulfonate ([BsAIm][OTf]) was immobilized on MPS-SCF via free radical addition. The obtained MPS-SCF and [BsAIm][OTf]/SCF were characterized by FT-IR, XRD, TEM, VSM, elemental analysis and N2 adsorption–desorption measurements. The immobilization of [BsAIm][OTf] on MPS-SCF and the relationship between the sulfhydryl group (SH) loading of MPS-SCF and the ionic liquid loading of [BsAIm][OTf]/SCF were studied. The catalytic activities of [BsAIm][OTf]/SCF were evaluated through the esterification of oleic acid with straight-chain alcohols. The results showed that more modifications corresponded to an increase in the SH loading of MPS-SCF and a decrease in the average pore diameter and specific surface area of MPS-SCF. The more SH groups that were supported on MPS-SCF, the less ionic liquid was immobilized on [BsAIm][OTf]/SCF due to its smaller pore diameter, which hindered the diffusion and immobilization of [BsAIm][OTf]. Moreover, when the carbon number of the straight-chain alcohol increased, the mass-transfer resistance in [BsAIm][OTf]/SCF rapidly increased and the conversion of oleic acid significantly decreased under the same reaction conditions. [Copyright &y& Elsevier]

Abstract: The AC magnetic susceptibility of water is studied in the frequency range of 1kHz–1MHz at a low magnetic field. The results show a paramagnetic behavior between 500kHz and 1MHz for samples at 37°C and 25°C, which is surprising considering that water is believed to be diamagnetic. AC magnetic susceptibilities for ice and different salt solutions were investigated as well: in such cases the susceptibility is always negative and therefore, such samples remain diamagnetic. [Copyright &y& Elsevier]

Abstract: Single-phase samples of Ln 2−xCaxCoO4+δ (Ln = Pr3+ − Gd3+) around x∼1 have been prepared. For the first time, the phase field for these compounds has been defined using powder X-ray diffraction and a very narrow solid solution was observed. Under our synthetic conditions, the K2NiF4 structure was not formed for the large La3+ ion, or for compositions containing the smaller rare earths ions (

Abstract: A synthesis route to /ZrO2/Fe3O4/WO3 solid acid catalysts with magnetism is reported through chemical co-precipitation method. The obtained solid acid catalysts are characterized in detail by X-ray diffraction, Different Scanning Calorimetry (DSC), Transmission Electron Microscopy (TEM), Vibrating Sample Magnetometer (VSM), N2 adsorption–desorption, Temperature-Programmed Pesorption (TPD) of ammonia. The results show that the introduction of WO3 and Fe3O4 strongly inhibit the phase transformation of zirconia and improve the thermal stability of zirconia. Furthermore, the obtained materials present super-paramagnetism and magnetism. The super acid exhibits high catalytic activity in forming fructone by condensation. [Copyright &y& Elsevier]

Abstract: The structure, Raman spectroscopy, magnetization, and dielectric properties of delafossite-type oxide CuCr1−x Al x O2 have been characterized. It was found that Al substitution generates an anisotropic effect on the structure, besides magnetic dilution. The temperature dependence of all samples exhibits paramagnetic behavior at high temperature. Above x=0.2 the ferromagnetic transition at 120K disappears. It is argued that Al substitution destabilizes the antiferromagnetic order of Cr3+ ions and modulates the spin configuration, leading to a weak ferromagnetism. The coupling between the magnetic order and ferroelectric order is also characterized. [Copyright &y& Elsevier]

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]

Abstract: We have developed a 25T pulsed high magnetic field system for soft X-ray Magnetic Circular Dichroism: XMCD. The ultra-high vacuum chamber with a pulse magnet coil is installed. By using a newly developed bipolar capacitor bank, the XMCD of paramagnetic Gd2O3 at the M 5 and the M 4 edges was clearly observed at low temperatures. The present system is capable of measuring XMCD of field induced moments in various compounds including paramagnets and antiferromagnets. [Copyright &y& Elsevier]

Abstract: Chitosan (CS) rods are a good candidate as temporary mechanical supports in bone regeneration, however the bending strength and bending modulus should be improved to match commercially available devices used for bone fracture internal fixation. Poly(p-amino-phenylacetylene)/multi-walled carbon nanotubes (PaPA/MWCNTs) hybrids with superparamagnetic Fe3O4 nanoparticles (Fe3O4@PaPA/MWCNTs) are applied to reinforce the CS rods. Fe3O4@PaPA/MWCNTs could be uniformly dispersed in CS solution and aligned by an external magnetic field, in the direction parallel to the axis of CS rod. This greatly helped to resist the bending stress, thus the bending strength and modulus of the reinforced CS rods are 124.6MPa and 5.3GPa, respectively; which are 34.8% and 29.3% stronger than pure CS rods. As a result, the magnetic-field-assisted in situ precipitation method offers one feasible route for the reinforcement of CS-based devices with nano-scaled one-dimensional additives such as MWCNTs. In addition, CS-based biomaterials containing Fe3O4@PaPA/MWCNTs could obviously promote MG63 cells proliferation, so CS rods modified with Fe3O4@PaPA/MWCNTs are good candidates for bone fracture internal fixation. [Copyright &y& Elsevier]

Abstract: Selective substitution of the chlorine atom coordinated to cobalt in the paramagnetic Mo3(CoCl)S4(dmpe)3Cl3 (dmpe=1,2-bis(dimethylphosphanyl) ethane) complex with a S =1/2 ground state has been achieved by iodine oxidation to afford the also paramagnetic [Mo3(CoI)S4(dmpe)3Cl3]I ([1]I) salt with a S =1 ground state in almost quantitative yield. Replacement of chorine by iodine has no significant effect on the structural and electrochemical properties of the Mo3CoS4 system. Metathesis of the [1]I salt with the paramagnetic nickel anionic dithiolate [Ni(mnt)2]− (mnt=maleonitrilodithiolate) affords [1]2[Ni(mnt)2]. The stoichiometry evidenced by X-ray analysis reveals that reduction of the [Ni(mnt)2]− radical to the corresponding diamagnetic closed shell [Ni(mnt)2]2− dianion, presumably via dismutation, has occurred during the metathesis process. The crystal structure of [1]2[Ni(mnt)2] consists of [Ni(mnt)2]2− dianions sandwiched by two cluster 1 + cations which yield {1 +·[Ni(mnt)2]2−·1 +} subunits arranged along the crystallographic c axis. Magnetic susceptibility measurements for [1]2[Ni(mnt)2] show a χT product of 0.99emuK/mol largely unchanged in the 10–300K range. This behavior agrees with the presence of an S =1 cluster 1 + cation while the Ni(mnt)2 moiety does not contribute to the paramagnetism of the sample. [ABSTRACT FROM AUTHOR]

Abstract: The 5d-transition metal, Ir has successfully been doped at Fe site and induced superconductivity in GdFeAsO at T c =18.9K and ∼20 atom%. The Ir-doping shortened the c-axis length and stretched the a-axis one, which led to enhance the coupling between the FeAs- and SmO-layer, and to weaken the bonding between Fe and As atom. Paramagnetism was observed in all of the samples, which was resulted from the magnetic Gd ion as in the F-doped GdFeAsO. An upper critical field of GdFe0.8Ir0.2AsO was extrapolated to around 24T, much smaller than that of F-doped GdFeAsO owing to a relatively low T c and small value of dH c2/dT. [ABSTRACT FROM AUTHOR]

Abstract: Iron disilicide has been found to exhibit superparamagnetism in nanoparticles, even though no magnetic ordering occurs in bulk. The unexpected behavior was attributed, based on magnetic studies, to chemical disorder. A lack of sextet-type signals in Mössbauer spectra supports that the observed magnetic order is confined to only a very small fraction of magnetic Fe ions. Moreover, quadrupole-splitting and isomer-shift parameters reveal a significant amount of Fe in a short-range α-FeSi2 structure, while XRD suggests an overall β-FeSi2 structure. Such a compositional heterogeneity is also reflected in a calorimetrically obtained spin-glass-like anomaly at low temperatures. Meanwhile, as the particle size decreases, specific heat and Sommerfeld constant are enhanced due to lattice softening and the emergence of surface charge density of states, respectively, in nanoparticles. [Copyright &y& Elsevier]