Temperature Dependence Of Magnetization Research Articles

The Magnetic Properties and Magnetocaloric Effect of Pr0.7Sr0.3MnO3 Thin Film Grown on SrTiO3 Substrate

The magnetic behaviors and magnetocaloric effect (MCE) of Pr0.7Sr0.3MnO3 (PSMO-7) film grown on a (001) SrTiO3 single-crystal substrate by a pulsed laser deposition (PLD) were studied in this paper. X-ray diffraction with a high resolution (HRXRD) measurement shows that PSMO-7 film is grown with a (001) single orientation. The magnetic properties and the MCE related to the ferromagnetic (FM) phase transition of the PSMO-7 film are investigated using the temperature dependence of magnetization M(T) and the magnetic field dependence of magnetization M(H). The M(T) data suggest that with decreasing temperatures, the PSMO-7 film goes through the transition from the paramagnetic (PM) state to the FM state at around the Curie temperature (TC). The TC (about 193 K) can be obtained by the linear fit of the Curie law. Magnetic hysteresis loop measurements show that the PSMO-7 film exhibits the FM feature at temperatures of 10, 100, and 150 K (low magnetic hysteresis can be found), while the film reveals the PM feature with the temperature increased up to 200 and/or 300 K. The research results of M(H) data are consistent with the M(T) data. Furthermore, the magnetic entropy change (-ΔSM) of the PSMO-7 film was studied. It was found that the maximum value of (-ΔSM) near TC reaches about 4.7 J/kg·K under the applied field change of 20 kOe, which is comparable to that of metal Gd (-ΔSM of 2.8 J/kg K under 10 kOe), indicating the potential applications of PSMO-7 film in the field of magnetic refrigeration.

Study on the magnetic and hysteresis behaviors in a bilayer graphene-like ring with edge decorated

We employed the effective-field theory with correlations to study the hysteresis and thermodynamic properties of a bilayer graphene-like ring with edge decorated by a ferrimagnetic mixed-spin (2, 5/2) Ising model. The temperature dependence of magnetization, susceptibility, internal energy and specific heat of the system are illustrated in detail. As well, we depict the hysteresis behaviors and phase diagram with various parameters. The results showed the significance of the anisotropy, the magnetic field as well as the exchange coupling in controlling hysteresis behaviors and various magnetic quantities. The possibility of rich multiple-loop hysteresis and reentrant behaviors are found, sensitive to the competition among the physical parameters.

Complex magnetic behavior in Ho2Re3Si5 single crystal

We report on the magnetic, electrical transport, and thermal properties of ${\mathrm{Ho}}_{2}{\mathrm{Re}}_{3}{\mathrm{Si}}_{5}$ single crystal by means of magnetization, electrical resistivity, and heat capacity measurements in the temperature range 2--300 K. Magnetic susceptibility, heat capacity, and electrical resistivity reveal two closely spaced antiferromagnetic transitions at ${T}_{\mathrm{N}1}\ensuremath{\sim}$ 3.8 K and ${T}_{\mathrm{N}2}\ensuremath{\sim}$ 4.2 K. Three field-induced metamagnetic transitions at 4.5, 10, and 15 kOe, in the magnetically ordered state at 2 K, have been observed, in the isothermal magnetization, for ${\ensuremath{\mu}}_{0}H\ensuremath{\parallel}c$, and their first-order nature is evident from the magnetic hysteresis. The hysteresis disappears and metamagnetic transitions become feeble at around 3.5 K. These metamagnetic transitions are consistent with field-induced magnetic phases as observed in the magnetic susceptibility, electrical resistivity, and heat capacity. The magnetization for ${\ensuremath{\mu}}_{0}\phantom{\rule{0.16em}{0ex}}H\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}a$ is linear without any signature of metamagnetic transition for fields up to 70 kOe suggesting the hard axis of magnetization. From the temperature dependence of the isothermal magnetization, we have constructed a magnetic phase diagram, which signals a complex magnetic structure in this compound. These results suggest that magnetic and transport properties are highly sensitive to the external magnetic field.

Structural, thermo-electric, and thermo-magnetic characteristics of non-stoichiometric L21-type Fe43Mn29Si28 Heusler structures

The structural, thermo-electrical, and thermo-magnetic characteristics of non-stoichiometric L21-type Fe43Mn29Si28 Heusler-type alloy, as bulk and glass-coated microwire by employing temperature-dependent electrical resistivity, relative permeability and magnetization measurements. Interestingly, the temperature dependence of electrical resistivity experiments on Fe43Mn29Si28 alloy under a heating-cooling cycle showed a clear temperature hysteresis in the temperature range of 149–226 K, corresponding to the martensitic-austenite phase transformation. During the martensitic transformation, the relative permeability of glass-coated Fe43Mn29Si28 microwire varies significantly by 2350% which much higher than the bulk Fe43Mn29Si28 alloy value of about 940%. Further magnetization experiments on both bulk and glass coated Fe43Mn29Si28 Heusler alloys measured at 0.05 kOe reveal a hysteresis of magnetization during heating and cooling process in the temperature range of 181–194 K attributed to martensitic transformation. Magnetic hysteresis measured at 5 K shows that the bulk Fe43Mn29Si28 alloy coercivity is 44 Oe which is magnetically softer than the glass-coated Fe43Mn29Si28 microwire with Hc = 110 Oe. The observation of martensitic transformation in bulk and glass-coated Fe43Mn29Si28 wire would be useful for developing common actuator and sensing applications.

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

A Three-Dimensional Silicon-Diacetylene Porous Organic Radical Polymer

Magnetism and microstructure of co-deposited yttrium iron garnet-barium titanate films

Yttrium iron garnet (YIG) and barium titanate (BTO) were co-deposited on (001)-orientated gadolinium gallium garnet substrates by pulsed laser deposition with composition determined by the ratio of laser shots ablating each target. With increasing shot ratios of YIG/BTO = 2.5/1, 4/1, 20/1, and 30/1, the majority phase in the film changes from textured polycrystalline perovskite to epitaxial garnet. Cross-sectional STEM characterization of the YIG-rich films reveals three distinct sublayers: the bottom layer is a coherent epitaxial garnet layer with higher unit cell volume than that of YIG; the second layer is garnet exhibiting crystalline defects and misorientation; and the upper layer is amorphous. Highly defective regions within the second layer are richer in Ba, suggesting that the microstructure is promoted by the insolubility of Ba in YIG. Temperature-dependent magnetization measurements fitted to a super-exchange dilution model indicate the presence of nonmagnetic Ti and vacancies in both octahedral and tetrahedral sites.

Possible origin of extremely large magnetoresistance in the topological insulator CaBi2 single crystal

CaBi2 has been experimentally found to be a superconductor with a transition temperature of 2 K and identified as a topological insulator via spin- and angle-resolved photoemission spectroscopy, which makes it a possible platform to study the interplay between superconductivity and topology. But the detailed transport properties for CaBi2 single crystal remain unexplored in experiments. Here, we systematically studied the magneto-transport properties of CaBi2 single crystal grown by a flux method. CaBi2 shows a magnetic-field-induced upturn behavior with a plateau in resistivity at low temperature. An extremely large and non-saturating magnetoresistance up to ∼15000% at 3 K and 12 T was achieved. The possible reason for the magnetic field and temperature dependence of resistivity and extremely large magnetoresistance at low temperature was discussed by adopting the Kohler’s scaling law, which can be understood by the compensation effect confirmed by the Hall Effect measurement.

The evolution of structure and magnetic properties of GdCr1-Fe O3 (0 ≤ x ≤ 0.5) polycrystalline samples

In this paper, the evolution of crystal structures and magnetic properties of GdCr 1- x Fe x O 3 (0 ≤ x ≤ 0.5) samples with different doping levels was systematically investigated by powder X-ray diffraction, Fourier transform infrared spectra, positron annihilation spectra, and temperature-dependent and field-dependent magnetization measurements. The lattice constants and Cr(Fe)O 6 octahedral deformation increase with Fe doping showing an anomaly at x = 0.4 which is further confirmed by positron annihilation and Fourier transform spectra. Fe doping in GdCrO 3 can suppress the magnetization reversal in the parent phase as well as its antiferromagnetic ordering temperature T N at low doping levels but enhance T N at high doping levels. A possible spin flip or flop transition under field-cooled-cooling process occurs for the samples of x = 0.3 and 0.4 at low temperature. The coercive fields of weak ferromagnetic state with different doping levels at 10 and 100 K also exhibit a local maximum at around x = 0.4 which is accordingly correlated to the concentrations of the vacancy defects in the sample. • The information of cationic vacancy defects is analyzed by positron annihilation technique. • The correlation between lattice parameters and vacancy defects is unveiled. • Defects in GdCr 1- x Fe x O 3 samples have a great impact on their magnetic properties. • Chemical doping and defect engineering are effective tools to manipulate R CrO 3 materials.

Theory of thermal properties of magnetic materials with unknown entropy

Theoretical approaches to study thermal properties of magnetic materials typically require accurate models of magnetic interactions in order to define the entropy. Here we introduce a complementary approach for examining thermal properties in magnetic systems where an accepted model for such interactions does not exist. In place of a specific model for magnetic interactions, the approach integrates measurements of temperature dependent magnetization of the studied material into a first principles computational scheme. The approach calculates system pressure from thermally disordered microstates that properly incorporate vibrational and spin subsystems at each temperature as well as the coupling between these subsystems. We apply the approach to calculate phonon modes and to investigate the anomalously low thermal expansion of the classical Invar alloy ${\mathrm{Fe}}_{0.65}{\mathrm{Ni}}_{0.35}$. The calculated phonon dispersions for Invar are in excellent agreement with measured data. The Invar thermal expansion is shown to remain small between 50 K and room temperature, consistent with the experimentally observed low thermal expansion value in this same temperature range. This anomalously small thermal expansion is directly connected to a small positive contribution from lattice thermal disorder that is nearly canceled by a large negative magnetic disorder contribution. By contrast, calculations for bcc Fe show a much larger thermal expansion, consistent with experiment, which is dominated by a large contribution from lattice thermal disorder that is reduced only slightly by a small negative contribution from that of magnetism. These findings give insight into the unusual nature of magnetism and spin-lattice coupling in Invar and Fe. In addition, they give promising preliminary support to the presented methodology as a complementary way to investigate thermal properties of magnetic materials. The success achieved on Invar and Fe motivates future testing of the approach on other magnetic materials.

Hyperthermia of Magnetically Soft-Soft Core-Shell Ferrite Nanoparticles

Magnetically soft-soft MnFe2O4-Fe3O4 core-shell nanoparticles were synthesized through a seed-mediated method using the organometallic decomposition of metal acetyl acetonates. Two sets of core-shell nanoparticles (S1 and S2) of similar core sizes of 5.0 nm and different shell thicknesses (4.1 nm for S1 and 5.7 nm for S2) were obtained by changing the number of nucleating sites. Magnetic measurements were conducted on the nanoparticles at low and room temperatures to study the shell thickness and temperature dependence of the magnetic properties. Interestingly, both core-shell nanoparticles showed similar saturation magnetization, revealing the ineffective role of the shell thickness. In addition, the coercivity in both samples displayed similar temperature dependencies and magnitudes. Signatures of spin glass (SG) like behavior were observed from the field-cooled temperature-dependent magnetization measurements. It was suggested to be due to interface spin freezing. We observed a slight and non-monotonic temperature-dependent exchange bias in both samples with slightly higher values for S2. The effective magnetic anisotropy constant was calculated to be slightly larger in S2 than that in S1. The magnetothermal efficiency of the chitosan-coated nanoparticles was determined by measuring the specific absorption rate (SAR) under an alternating magnetic field (AMF) at 200-350 G field strengths and frequencies (495.25-167.30 kHz). The S2 nanoparticles displayed larger SAR values than the S1 nanoparticles at all field parameters. A maximum SAR value of 356.5 W/g was obtained for S2 at 495.25 kHz and 350 G for the 1 mg/mL nanoparticle concentration of ferrogel. We attributed this behavior to the larger interface SG regions in S2, which mediated the interaction between the core and shell and thus provided indirect exchange coupling between the core and shell phases. The SAR values of the core-shell nanoparticles roughly agreed with the predictions of the linear response theory. The concentration of the nanoparticles was found to affect heat conversion to a great extent. The in vitro treatment of the MDA-MB-231 human breast cancer cell line and HT-29 human colorectal cancer cell was conducted at selected frequencies and field strengths to evaluate the efficiency of the nanoparticles in killing cancer cells. The cellular cytotoxicity was estimated using flow cytometry and an MTT assay at 0 and 24 h after treatment with the AMF. The cells subjected to a 45 min treatment of the AMF (384.50 kHz and 350 G) showed a remarkable decrease in cell viability. The enhanced SAR values of the core-shell nanoparticles compared to the seeds with the most enhancement in S2 is an indication of the potential for tailoring nanoparticle structures and hence their magnetic properties for effective heat generation.

Correlated temperature and field dependent magnetization: Enhanced magnetic hysteresis upon Dy doping in La-based francisite Cu3La(SeO3)2O2Cl

Study of La-based cuprate francisite (LaCufr), an analogue compound of Cu3Bi(SeO3)2O2Cl, is interesting due to the interplay of competing magnetic interactions in this geometrically frustrated layered compound. The motivation is to investigate the role of rare earth metals with 4f electrons on Cu2+ ions with 3d electrons, i.e., to study a complex 3d-4f interaction. In this regard, pristine, 5, and 10 at% (atomic percentage) Dy doped La-based cuprate francisite [Cu3La1-xDyx(SeO3)2O2Cl; x = 0, 0.05, and 0.1] compounds were synthesized. Structural (X-ray diffraction i.e. XRD), electronic (X-ray absorption near edge structure i.e. XANES) and magnetic properties were investigated. XRD and XANES ensure phase purity and indicate dopant Dy atoms are more or less substitutionally incorporated at the La site. Magnetic properties were highlighted by unconventional magnetic hysteresis due to spin reorientation transition (SRT) and field-induced meta-magnetic transition (MMT) below 15 K. The signature of MMT was also observed from a temperature dependent magnetization (M−T) study, which is unique. The process of field dependent magnetization has been explored with a spin flop and spin flip transition. Dy doping enhances hysteresis and overall magnetization. The reason for this enhancement has been interpreted as identifying micro-interactions using an energy splitting scheme.

Phase transformations and magnetostriction in Fe100−xGax bulk alloys

Fe–Ga alloys, containing 18, 21, and 23 at.% of Ga, were prepared in bulk form. In their as-cast state, they display a small magnetostriction, that is strongly improved after annealing at 1000 °C for 24 h, and subsequent rapid cooling. Multiple characterization techniques, such as x-ray diffraction, differential scanning calorimetry, Mössbauer spectroscopy, temperature-dependent magnetization curves, hysteresis loops, magnetic force microscopy, and magnetostriction measurements, were exploited in synergy to gain a deep understanding of the structure–property relationships in the studied alloys, before and after annealing. The A2 phase, which is favored in the lower range of compositions and is promoted at the expense of the D03 one by annealing, is responsible for characteristic dendritic and maze magnetic domains, and for the strong improvement of the magnetostriction, which almost reaches 240 ppm (transverse configuration) in the alloys with 18 at.% of Ga, after annealing.

Static and dynamic magnetic properties of the spin- triangle lattice antiferromagnet Na3Fe(PO4)2 studied by 31P NMR

31P nuclear magnetic resonance (NMR) measurements have been carried out to investigate the magnetic properties and spin dynamics of Fe3+ (S = 5/2) spins in the two-dimensional triangular lattice (TL) compound Na3Fe(PO4)2. The temperature (T) dependence of nuclear spin-lattice relaxation rates () shows a clear peak around Néel temperature, K, corresponding to an antiferromagnetic (AFM) transition. From the temperature dependence of NMR shift (K) above , an exchange coupling between Fe3+ spins was estimated to be K using the spin-5/2 Heisenberg isotropic-TL model. The temperature dependence of divided by the magnetic susceptibility (χ), , above proves the AFM nature of spin fluctuations below in the paramagnetic state. In the magnetically ordered state below , the characteristic rectangular shape of the NMR spectra is observed, indicative of a commensurate AFM state in its ground state. The strong temperature dependence of 1/T 1 in the AFM state is well explained by the two-magnon (Raman) process of the spin waves in a 3D antiferromagnet with a spin-anisotropy energy gap of 5.7 K. The temperature dependence of sublattice magnetization is also well reproduced by the spin waves. Those results indicate that the magnetically ordered state of Na3Fe(PO4)2 is a conventional 3D AFM state, and no obvious spin frustration effects were detected in its ground state.

(Ba1−x Na x )F(Zn1−x Mnx)Sb: A novel fluoride-antimonide magnetic semiconductor with decoupled charge and spin doping

We report the successful synthesis and characterization of a novel 1111-type magnetic semiconductor (Ba1−x Na x )F(Zn1−x Mn x )Sb (0.05 ≤ x ≤ 0.175) with tetragonal ZrSiCuAs-type structure, which is isostructural to the layered iron-based superconductor La(O,F)FeAs. Na substitutions for Ba and Mn substitutions for Zn introduce carriers and local magnetic moments, respectively. Ferromagnetic interaction is formed when Na and Mn are codoped, demonstrating that local magnetic moments are mediated by carriers. Iso-thermal magnetization shows that the coercive field is as large as ~ 12 000 Oe, which is also reflected in the large split between the temperature-dependent magnetization in zero-field-cooling and field-cooling condition. AC susceptibility under zero field demonstrates that samples evolve into spin-glass state below spin freezing temperature T f. The measurements of temperature-dependent resistivity indicate that (Ba1−x Na x )F(Zn1−x Mn x )Sb exhibits semiconducting behaviour.

Influence of twin-crystal structures on the temperature dependence of magneto-optic Kerr effect and magnetic anisotropy in epitaxial Ni thin films

We report on the enhanced Curie temperature and magnetic anisotropy observed in the temperature dependence of magneto-optic Kerr effect (MOKE) in epitaxial Ni films grown on single-crystal c-cut sapphire Al2O3 (0001) substrates. X-ray diffraction (XRD) revealed the epitaxial growth of Ni (111) on Al2O3 (0001) substrate while XRD azimuthal scans indicated the presence of 60°-rotated twin-crystal structures of fcc Ni in ABC…and ACB… stacking in the Ni/Al2O3 (0001) film. Twin-crystal structures were also revealed from the surface morphology of the Ni (111) layer in the Ni/Al2O3 (0001) film. MOKE hysteresis loops indicated higher Kerr remanence with lower coercivity for the Ni/Al2O3 (0001) film as compared to the polycrystalline Ni film grown on Si (100) substrate under the same conditions. Azimuthal MOKE hysteresis loops confirmed the presence of 2-fold in-plane magnetic anisotropy in the Ni/Al2O3 (0001) film. Temperature dependent MOKE measurements in the range of 300– 680 K revealed a power-law dependence of the Kerr remanence similar to magnetization. The Curie temperature (TC) of the Ni/Al2O3 film was found to be almost 10 K higher than bulk Ni. In- and out-of-plane magnetization revealed a uniaxial perpendicular magnetic anisotropy with the easy axis along the Ni/Al2O3 film plane. The calculated values of the anisotropy constants revealed a high degree of magnetocrystalline anisotropy in the epitaxial Ni/Al2O3 (0001) film. A close correlation of MOKE and magnetization hysteresis loops indicated similar surface and volume magnetic behaviors in the thin films. The enhanced temperature dependent MOKE, magnetocrystalline anisotropy and magnetization could be attributed to the twin-crystal structures in the epitaxial Ni/Al2O3 film.

Structure and magnetic properties of (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)3O4 nanocrystalline high-entropy oxide synthesized using a sol-gel auto combustion approach

A sol–gel auto-combustion method is used in this study to synthesize a new class of single-phase high-entropy oxide (HEO) (Mg1/6Zn1/6Mn1/6Co1/6Ni1/6Fe1/6)3O4. The as-synthesized compound exhibits a single-phase spinel structure with an 8.3224 Å lattice parameter and an average crystallite size of 10 nm as determined by X-ray diffraction (XRD) data analysis. Raman and Fourier transform infrared results are in agreement with the XRD results. A scanning electron microscopy-based energy dispersed spectroscopy study suggests the formation of a porous structured morphology with a uniform elemental distribution. In addition, high-resolution transmission electron microscopy and surface analyses further confirm the formation of a pure spinel structure with a particle size of 12–20 nm and a mesoporous character with a pore size of 4.55 nm. X-ray photoelectron spectroscopy indicates mixed-valence states of elements (Mn, Fe, Co, and Ni) and their occupations over tetrahedral and octahedral sites. The temperature-dependent magnetization exhibited a bifurcation between zero-field-cooled and field-cooled magnetizations. From the M−H curves, the magnetization decreased monotonically with the increase in temperature (M is 22 emu/g at 2 K and 7.2 emu/g at 300 K). The coercivity decreased by approximately-one order of magnitude (HC = 1700 Oe at 2 K and HC = 200 Oe at 370 K). Finally, a comprehensive magnetic characterization of the as-synthesized HEO indicates their ferrimagnetic nature. The novel physical properties of the as-synthesized HEO could be useful in various potential applications.

Structural, electrical and magnetic properties of orthorhombic GdMn1-xNixO3 (0 ≤ x ≤ 0.1): Influence of Ni doping

GdMn1-xNixO3 (0 ≤ x ≤ 0.1) samples were synthesized by traditional solid state reaction method to understand the role of Ni substitution on structural, microstructural, electrical and magnetic properties. Powder X-ray diffraction data reveals the perovskite type structure with pnma space group for all the prepared samples. Scanning electron micrographs shows combined island and disc like granular structures. Raman spectroscopy reveals enhancement in asymmetric stretching mode due to out of phase MnO6 bending and bending mode due to O2 anti-stretching. The temperature dependent dc electrical resistivity confirms the semiconducting nature of the samples, supported by small polaron hopping (SPH) and variable range hopping (VRH) conduction models. The activation energies first increases and then decreases with Ni content. Temperature dependent magnetization under ZFC and FC regimes shows decrement in Tirr with Ni concentration. Currie-Weiss law fittings to inverse of susceptibility data indicates the paramagnetic nature of the samples with presence of antiferromagnetic interactions at 5 K.

A chiral alkali metal capped Ni4 cubane complex: Synthesis, structure, magnetic and catalytic bromination studies

A new chiral NaO2Ni4O2N2 cluster has been developed with a distorted capped cubane-type structure. The structure was determined by single crystal X-ray diffraction. The tetradentate Schiff-base ligand was synthesized by the condensation of o-vanillin and D-(-)‑threo-2-amino-1-(4-nitrophenyl)-1,3-propanediol. X-ray structure reveals that the complex possesses a Ni4 cubane cluster where sodium ion is anchored on the face of the cubane structure. Continuous shape measurement studies revealed that all the Ni centres are in distorted octahedral geometry and sodium ion adopts the spherical square pyramidal geometry. Further structural exploration reveals that the complex shows local distortions of the coordination geometries at each metal site, and these distortions govern the magnetic anisotropy associated with each NiII ion. For the present case, an elongation (dstr > 0) of the octahedral coordination sphere results in a local easy-plane anisotropy, with a positive DNi(II) parameter. Temperature dependant magnetization measurements showed a predominant ferromagnetic interaction amongst the four Ni centres. This complex is also catalytically active towards bromination of aromatic phenolic compounds. Initial catalytic activity was verified with the conversion of phenol red to bromophenol blue. Different phenolic substances show good conversion to their corresponding bromo derivatives. The complex showed good catalytic activity towards bromination of aromatic phenolic compounds, offering up to 99% conversion with 100% selectively to their corresponding bromo derivatives.

Unraveling the nature of ferrimagnetism and associated exchange interactions in distorted honeycomb Ni4Nb2O9

Ferrimagnetism in orthorhombic ${\mathrm{Ni}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ below its N\'eel temperature, ${T}_{FN}\ensuremath{\sim}76\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is reported to result from two inequivalent ${\mathrm{Ni}}^{2+}$ ions having different magnetic moments. However, a clear understanding of the temperature variation of its magnetization $[M(T$)] for $T>{T}_{FN}$ and $T<{T}_{FN}$ in terms of a single set of exchange parameters is still lacking. In this work, experimental results obtained from a detailed analysis of the temperature and magnetic field dependence of magnetization $[M(T,H)$], ac-magnetic susceptibility [${\ensuremath{\chi}}_{\text{ac}}(f,T,H$)], and heat-capacity [${C}_{P}(T,H)$] measurements are combined with theoretical analysis to provide new insights into the nature of ferrimagnetism in ${\mathrm{Ni}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$. X-ray diffraction/Rietveld analysis of the prepared sample yielded the structural parameters of the orthorhombic crystal in agreement with previous studies, whereas x-ray photoelectron spectroscopy confirmed the ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Nb}}^{5+}$ electronic states in ${\mathrm{Ni}}_{4}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$. Analysis of ${\ensuremath{\chi}}_{\text{ac}}(T)$ shows the paramagnetic-to-ferrimagnetic transition occurs at 76.5 K (${T}_{FN}$), which increases with applied field $H$ as ${T}_{FN}\phantom{\rule{4pt}{0ex}}\ensuremath{\propto}\phantom{\rule{4pt}{0ex}}{H}^{0.35}$ due to the coupling of the ferromagnetic component with $H$. For $T>\phantom{\rule{4pt}{0ex}}{T}_{FN}$, the ${\ensuremath{\chi}}_{dc}$ versus $T$ data are fitted to the N\'eel's expression for ferrimagnets, yielding the $g$-factors for the two ${\mathrm{Ni}}^{2+}$ ions as ${g}_{A}=2.47$ and ${g}_{B}=2.10$. Also, the antiferromagnetic molecular field constants between the $A$ and $B$ sublattices were evaluated as ${N}_{AA}=26.31, {N}_{BB}=8.59$, and ${N}_{AB}=43.06,$ which, in turn, yield the antiferromagnetic exchange parameters: ${J}_{AA}/{\mathrm{k}}_{B}=4.27$ K, ${J}_{BB}/{\mathrm{k}}_{B}=1.40$ K, and ${J}_{AB}/{\mathrm{k}}_{B}=6.98$ K. For $T<{T}_{FN}$, the $M$ versus $T$ data clearly show the magnetic compensation point at ${T}_{\text{COM}}\ensuremath{\sim}33$ K. The mathematical model presented here using the magnitudes of ${N}_{AA}, {N}_{BB}$, and ${N}_{AB}$ correctly predicts the position of ${T}_{\text{COM}}$ as well the temperature variation of $M$ both above and below ${T}_{\text{COM}}$. The data of ${C}_{P}(T$) versus $T$ shows a $\ensuremath{\lambda}$-type anomaly across ${T}_{FN}$. After subtracting the lattice contribution, the ${C}_{P}(T$) data are fitted to ${C}_{P}=A{(T\ensuremath{-}{T}_{N})}^{(\ensuremath{-}\ensuremath{\alpha})}$ yielding the critical exponent $\ensuremath{\alpha}=0.14(0.12)$ for $T<{T}_{FN}(T>{T}_{FN}),$ which is a characteristic of second-order phase transition. Magnetic entropy changes determined from the $M\text{\ensuremath{-}}H$ isotherms shows that the applied field $H$ enhances the magnetic ordering for $T>{T}_{FN}$ and $T<{T}_{\text{COM}}$, but for ${T}_{COM}<T<{T}_{FN}$, the spin disorder increases with the increase in $H$. The temperature variation of the measured coercivity ${H}_{C}(T$) and remanence ${M}_{R}(T$) from 1.9 K to ${T}_{FN}$ initially show a decreasing trend, becoming zero at ${T}_{\text{COM}}$, then followed by an increase and eventually becoming zero again at ${T}_{FN}$.

Synthesis and characterization of bifunctional Ru doped La-based perovskites for magnetic refrigeration and energy storage systems

In this study, the effect of Ru additive on the crystallographic, magnetic, and electrocatalytic properties of LaBiBaMnO3 manganite was investigated for magnetic refrigeration and energy storage systems. XRD analysis of La0·62Bi0·05Ba0·33MnO3 (LBBM) and La0·62Bi0·05Ba0·33Mn0·90Ru0·10O3 (LBBMR) manganites prepared by solid state method reveals that the samples have a rhombohedral structure and the average grain size of perovskites are found to be below 3 μm. From the temperature-dependent magnetization measurements, it was observed that the value of Curie temperature (TC) decreased from 334 K for LBBM to 327 K for LBBMR with the substitution of Mn with 10% Ru. In parallel with the decrease observed in TC with Ru contribution, a decrease in magnetic entropy value was also observed. The substitution of 10% Ru reduced the onset potential 51 mV for oxygen evolution reaction (OER) and 74 mV for oxygen reduction reaction (ORR). The electrode activity of OER at 10 mA cm−2 was obtained at around 0.976 V. Ru substitution and increasing scan rate to 100 mV s−1 increased the current density and lowered onset potential for OER. The ORR efficiency of LBBM catalysts boosted up to 60% with the durability test for 6 h. The increased cathodic Tafel slope from −255.1 mV dec−1 to −120.4 mV dec−1 with 10% Ru substitution suggests that a fast charge transfer for ORR activity due to Ru-occupied Mn-sites in the structure. LBBMR sample achieved bifunctional properties as ORR/OER performance and magnetic cooling applications by substituting Mn with 10% Ru.