Temperature-dependent Magnetic Behavior Research Articles

Structural and physical properties of Ni 1−x V x alloys around and away from quantum critical point

We investigate the room temperature structure (global and local), temperature dependent magnetic and transport behaviour of Ni 1−x V x ( 0⩽x⩽0.13 ) alloys. Our Energy Dispersive Analysis of x-rays results show that the prepared compositions are stoichiometric. With increase in V doping, the compounds exhibit a quantum phase transition around x c = 0.12, where the ferromagnetic phase is suppressed. Our results show that all the compounds stabilize in face centred cubic structure at RT and the lattice parameter shows unusual behaviour close to x c . The magnetic and heat capacity studies show signature of Griffiths phase on either side of x c . From 25 K to the lowest collected temperature, we observe a linear T dependence of resistivity at x = 0.1 and around x c , which is separated by a Fermi-liquid region around x = 0.106. This suggests that the origin of the transport behaviour is different around the quantum critical point and away from it. Our Ni K-edge x-ray Absorption Spectroscopy results show that there is a significant reduction in the first coordination number around Ni central atom on doping. Further, with doping, there is distortion in the first coordination shell around Ni. This suggests, with V doping, the local structure around Ni is different from the global structure as obtained from the x-ray Diffraction results. Interestingly, with doping, we observe a direct connection between the extent of distortion at RT and the magnetic disorder obtained at 2 K. We believe our results will motivate the scientific community to further study the interplay between the structural disorder and quantum fluctuations with temperature at the local level.

Temperature-dependence of anomalous Hall effect in Ta-(GdFeCo)δ-Ta films with vertical composition gradients

Ferrimagnetic rare-earth (RE) – transition-metal (TM) alloys are considered small ferromagnets with antiferromagnetic exchange in sublattices, which makes them a preferable choice for future ultrafast memory-related applications. Here, we explore the magnetic properties of two GdFeCo thin films with tailored vertical composition gradients, achieved by gradually varying Gd concentration across the film thickness. The temperature-dependent magnetic behavior of these films is investigated using anomalous Hall effect (AHE) measurements and SQUID magnetometry. Both films exhibit perpendicular magnetic anisotropy with distinct coercivities, indicating variations in their magnetic properties. The films show RE-dominant behavior at 300 K. Moreover, for the positive composition gradient (+δ) film, the compensation temperature is around 350 K, while the film with a negative gradient (−δ) exhibits a compensation temperature above 400 K. Furthermore, the spin-flop behavior and AHE sign reversal provide insights into the sublattice dominance and exchange interactions within the films. The magnitude of ΔRXY (the difference in AHE resistance at different magnetic fields) is shown to be sensitive to the composition gradient, indicating stronger perpendicular magnetic anisotropy for the “−δ” sample. This study demonstrates the potential of composition engineering to tailor the magnetic characteristics of ferrimagnetic materials for specific spintronics applications.

Correlating structural and magnetic ground states of 3d-5d based double perovskites: Evidence of two magnetic phase transitions

We present a detailed study on both the structural and magnetic properties of the Sr2RuMn1-xIrxO6double perovskite oxides with four different concentrations (x = 0, 0.25, 0.5 and 0.75). The main objective of the work is to study the effect of Ir substitution for Mn on the high-temperature crystallographic and low-temperature magnetic phases of the compounds. Thephase purity was confirmed by the Rietveld analysis of the X-ray diffraction (XRD)pattern. The high temperature crystallographic information of the compounds was investigated by the help of high temperature X-ray diffraction and Raman spectroscopy. Signature of two structural phase transitions for x = 0.75 and one structural phase transition for x = 0 was seen. FESEM (Field emission scanning electron microscopy) with EDS (energy dispersive spectroscopy) of Ir-01 (x = 0.25) confirmed the presence of all the elements in the sample. The magnetic structure of all the samples have been studied at low temperature (5 K). The existence of two magnetic transitions for x = 0.5 and x = 0.75 are evident from the temperature dependent magnetization behavior.

Temperature-dependent magnetic and electrical behavior in the La0.50Pr0.50Mn0.8Co0.2O3 perovskite

Temperature-dependent magnetic and electrical behavior in the La0.50Pr0.50Mn0.8Co0.2O3 perovskite

Simulations of Temperature-Dependent Magnetization in FexGd100−x (20 ≤ x ≤ 80) Alloys

Theoretical calculations of the temperature-dependent magnetization in FeGd alloys were done with the use of Heisenberg-type atomistic spin Hamiltonian and Monte Carlo algorithms. The random allocation of atoms in the desired crystal structure was used for simulations of magnetically amorphous alloys. Performed calculations for the two different crystal structures have shown an important role of coordination number on the observed critical temperature and compensation point. Moreover, the value of the exchange interaction between Fe and Gd sublattices plays a key role in the simulations—an increase in the Fe–Gd exchange constant provides an increase in critical temperature for each concentration of elements, which explains the higher temperature stabilization of Gd moments. It was shown that obtained temperature-dependent magnetization behavior is consistent with experimental observations, which confirms the applicability of the atomic model used to study FeGd or other magnetic alloy structures.

Temperature-dependent Scaling Behavior of Magnetic Hysteresis Loop of CoFeB/Pd Multilayer Film

We report our experimental investigation on the temperature-dependent hysteresis loops and magnetic domain behaviors of CoFeB (0.4 nm)/Pd (1 nm) multilayer on polyimide substrate with a perpendicular magnetic anisotropy, by means of magneto-optical Kerr microscopy. Hysteresis characteristics such as saturation magnetization, coercivity, and hysteresis loop area with respect to the temperature have been analyzed, where powerlaw scaling behaviors are observed with microscopic magnetic domain patterns mediated by numerous nucleation sites.

Co, Fe and CoFe oxide nanoparticle assemblies within an ordered silica matrix: effects of the metal ions and synthesis pathway on the microstructure and magnetic properties

The magnetic properties of nanoparticle assemblies strongly depend on the structural and morphological characteristics of the individual nanoparticles as well as on their organization within the assembly. Here, we present the synthesis of cobalt and/or iron oxide nanoparticles within the ordered mesoporosity of a silica monolith by two different synthesis pathways (using either Prussian blue analogues or nitrate salts as a precursor). We describe the influence of the nature of the metal ion and of the synthesis pathway on the morphology of the nanoparticles. With respect to these observations, we present and discuss the temperature-dependent magnetic behaviors of the final nanocomposites.

XAS and XMCD Reveal a Cobalt(II) Imide Undergoes High-Pressure-Induced Spin Crossover

The spin crossover (SCO) transition is investigated in two molecular Co2+ bis-imide compounds, Co(dpzca)2 and Co(pypzca)2 (where Hdpzca = N-(2-pyrazylcarbonyl)-2-pyrazinecarboxamide and Hpypzca = N-(2-pyrazylcarbonyl)-2-pyridinecarboxamide). They crystallize solvent-free with similar crystal structures but have been reported to exhibit different temperature-dependent magnetic behaviors. Using temperature- and pressure-dependent element selective X-ray absorption spectroscopy (XAS and XMCD) measurements, it is revealed herein that although Co(pypzca)2 does not afford a temperature-induced SCO, it undergoes a reversible pressure-induced SCO transition that is less abrupt, and is complete at a higher pressure (3.5 GPa), than for Co(dpzca)2 (0.5 GPa). Wave function-based calculations performed on isolated complexes confirm the LS state nature of Co(dpzca)2 at low temperatures, and the values of spin and orbital magnetic moments are determined. Calculations show the similarity of ground-state properties for HS Co(dpzca)2 and HS Co(pypzca)2 and the existence of a double-well HS-LS in the potential energy surface for both compounds. It is concluded that the observed, significant differences in pressure- and temperature-induced SCO transitions of Co(dpzca)2 versus Co(pypzca)2 are probably due to different intermolecular interactions between Co(dpzca)2 and Co(pypzca)2, which would hamper the temperature-induced SCO in Co(pypzca)2.

A Molecule Having 13 Unpaired Electrons: Magnetic Property of a Gadolinium(III) Complex Coordinated with Six Nitronyl Nitroxide Radicals.

A gadolinium(III) complex coordinated with six nitronyl nitroxide radicals showed intriguing temperature-dependent changes in magnetic susceptibilities. The gadolinium(III) ion in the complex is pseudo-eight-coordinated by three singlet-ground-state diradical anion species based on nitronyl nitroxide radicals. The magnetic susceptibility (χpT) of the gadolinium(III) complex at 298 K, whose value corresponded to that of a system with 13 unpaired electrons (seven-spin system), decreased upon a lowering of the temperature to 11 K but increased upon a further lowering of the temperature. Finally, the χpT value at 2 K was found to be higher than that at room temperature. The temperature-dependent magnetic behavior could be explained by a structural change in the diradical anion ligand due to its flexibility.

Structural and Magnetic Phase Transitions in the Fe-Rich Compositional Range of the Multiferroic BiFe1- x [Zn0.5Ti0.5] x O3 Perovskites

The (1-x)BiFeO3-xBiZn0.5Ti0.5O3 solid solutions (0.05 ≤ x ≤ 0.25) were prepared using high-pressure synthesis. Up to 25 at.% substitutions of Fe by the combination of [Mg0.5Ti0.5] were found to increase the unit cell volume of the primitive perovskite cell, while the crystal structure remains the rhombohedral perovskite, as that in the parent BiFeO3. With increasing temperature, the as-prepared ceramics of the x = 0.25 composition reversibly transform into a cubic modification between about 970 and 1070 K. However, this phase transition is overlapped with a gradual decomposition of the perovskite phase, which starts above 770 K. The perovskite phase with the substitution rate corresponding to x = 0.25 is antiferromagnetic below T N∼460 K. Peculiarities of the temperature-dependent magnetic behavior of this composition at about 220 and 315 K, which might indicate transitions between the states with different magnetic orderings, have been observed.

Surface magnetic structure investigation of a nanolaminated Mn2GaC thin film using a magnetic field microscope based on Nitrogen-Vacancy centers

This work presents a magnetic field imaging method based on color centers in diamond crystal applied to a thin film of a nanolaminated Mn2GaC MAX phase. Magnetic properties of the surface related structures have been described around the first order transition at 214 K by performing measurements in the temperature range between 200 K and 235 K with the surface features fading out by increasing temperature above the transition temperature. The results presented here demonstrate how Nitrogen-Vacancy center based magnetic microscopy can supplement the traditionally used set of experimental techniques, giving additional information of microscopic scale magnetic field features, and allowing to investigate the temperature dependent magnetic behavior. The additional information acquired in this way is relevant to applications where surface magnetic properties are of the essence.

Temperature-dependent magnetic behavior of Mn-Mg spinel ferrites with substituted Co, Ni & Zn, synthesized by hydrothermal method

Mn0.1Mg0.2(Co, Ni, Zn)0.7Fe2O4 compounds with particles sizes ranging between 11 nm and 17 nm were successfully synthesised by hydrothermal process. These particles sizes are in agreement with TEM results. Bulk samples with particle sizes ranging between 69 nm and 72 nm were subsequently produced by annealing at 1100 °C under argon gas. SEM and EDX were used to study the morphology and confirm the elemental compositions. Temperature-dependent magnetization showed a strong dependence of coercive fields on measuring temperature and substituent. The coercive field variation followed Kneller's law with values varying between 0.5 kOe and 12 kOe from about 300 K to 2 K. An average moment of about ≈104 was deduced from the magnetic measurements of the as-prepared samples. Temperature-dependent magnetic measurements in as-prepared samples showed superparamagnetic behavior with. The Langevin function fittings on M-H data at 300 K give particle size distributions with average diameters corresponding well with that estimated from XRD analysis. Field cooling (FC) and zero-field cooling (ZFC) measurements showed the dependence of bifurcation temperature on the applied magnetic field.

Synthesis and characterization of a 30-membered decanuclear manganese metallacrown containing cyclopentane-carboxyl salicylhydrazide ligand

A new macrocyclic 30-metallacrown-10, [Mn10(cpshz)10(CH3OH)10]·2CH2Cl2·10CH3OH, has been prepared by supramolecular self-assembly using N-cyclopentane-carboxyl salicylhydrazide (H3cpshz) as the pentadentate ligands. Ten ligands chelate ten manganese(III) ions through the diaza bridging groups into a 30-membered [Mn–N–N]10 cyclic structure. The Mn(III) centers in the decanuclear ring exhibit alternating Λ and Δ configurations. The temperature-dependent magnetic behavior indicated that there are weakly antiferromagnetic couplings between the paramagnetic centers.

Effect of bismuth doping on the structural, magnetic, electrical, and thermopower behavior of lanthanum silver manganites

The structural, magnetic, electrical, and thermoelectric behaviors of lanthanum silver manganite and lanthanum bismuth silver manganite were thoroughly studied in the present work. Two polycrystalline samples, viz., La0.835Ag0.165MnO3 (LAMO) and La0.67Bi0.165Ag0.165MnO3 (LBAMO) possessing almost constant ratio of Mn3+/Mn4+ were synthesized using the wet chemical method. Phase formation was identified from powder X-ray diffraction and it has been confirmed through the structural analysis of which samples crystallize into rhombohedral symmetry with R-3C space group. Apparent changes at phase transition temperature were observed in temperature-dependent resistivity, magnetization and thermoelectric power behavior for bismuth-doped samples. In addition, an enhanced magnetoresistance was observed in LBAMO samples and is attributed to the presence of both ferromagnetic and anti-ferromagnetic states. The temperature-dependent resistivity data in the temperature range (50–300 K) were analyzed using the phase separation model. Spin-dependent scattering and electron–electron interactions were considered to explain the resistivity minimum in the low temperature region (T < 50 K). The Seebeck coefficient is positive and enhances around the transition temperature by substituting bismuth into LAMO. The high-temperature thermoelectric power data were explained in the framework of small polaron hopping mechanism while magnon drag effect dominates in the low temperature region.

Analysis of Ligand Field Effects in Europium(III) Phosphates

Optical spectra (powder reflectance, UV/Vis/NIR region), and temperature dependent magnetic behavior (χ, μ/μB) were recorded for the series of anhydrous europium(III) phosphates EuIII3O3(PO4), EuIIIPO4, EuIII2P4O13, lt‐ and ht‐EuIII(PO3)3, and EuIIIP5O14. By modeling within the AOM framework, the experimental data can be related to the ligand‐field splitting experienced by the Eu3+ ions in the various mainly low‐symmetry coordination environments. Our study confirms the well‐established relation eσ(Eu3+–O2–) ~ d(Eu3+–O2–)–7.0 between the AOM parameter and the interatomic distance. In addition it is shown that eσ(Eu3+–O2–) depends strongly on the highly variable polarizability of the oxygen ligator atoms. This polarizability can be related to the optical basicity Λ of the various phosphates.

Coupled phonons and magnetic orderings in GaFeO3: Raman and magnetization studies

Magnetoelectric (ME) materials with ferroelectric and magnetic transition temperatures near room temperature are of current interest in research due to their technological importance and potential applications. Herein, we report the coupled magnetic ordering and phonons in gallium ferrite (GaFeO3), a near room temperature ME perovskite, using magnetization and inelastic light scattering measurements as a function of temperature. Temperature-dependent magnetization behavior studied in a wide temperature range of 5–395 K at both field-cooled (FC) and zero-field-cooled (ZFC) conditions using different static magnetic fields confirms the magnetic transition temperature Tc at 220 K. On temperature dependent Raman spectroscopy, no significant changes in Raman spectra were observed at an elevated temperature that can be attributed to the absence of structural phase transition. Instead of expected anharmonic behavior, several librational (rigid rotation) and stretching modes of rigid BO6 units were found to be hardening below Tc, suggesting the significant magnetoelastic coupling contributions to phonon frequencies. The asymmetric stretching mode at 753 cm−1 is found to have larger spin-phonon coupling contribution (λ∼2.93), while the lattice mode at 153 cm−1 and external librational mode at 240 cm−1 had the lowest effect (λ∼0.88).

Magnetic behaviour of assemblies of interacting cobalt-carbide nanoparticles

Recent work [1] demonstrated high coercivity and magnetic moment in cobalt carbide nanoparticle assemblies and explained the high coercivity from first principles in terms of the high magnetocrystalline anisotropy of the cobalt carbide nanoparticles. In this work, we comprehensively model the interaction between the nanoparticles comprising the assembly and systematically understand the effect of particle size, distribution of the orientations of the nanoparticles’ magnetocrystalline anisotropy axis with respect to the applied magnetic field, and dipole coupling between nanoparticles on the temperature dependent magnetic behavior of the nanoparticle assembly. We show that magnetocrystalline anisotropy alone is not enough to explain the large hysteresis over the 50 K–400 K temperature range and suggest that defects and inhomogeneity that pin the magnetization could also play a significant role on this temperature dependent magnetic behavior.

Ni 3d – O 2p hybridization dependent magnetic properties of LaNiO3 thin films

We present here the study on magnetic properties and their relation to the electronic structure for c-axis oriented LaNiO3 films deposited on LaAlO3 single crystals using the rf-magnetron sputtering. Swift heavy ion irradiation induced annealing alters the unusual temperature dependent magnetic behaviour of pristine film to the paramagnetic one. X-ray absorption spectroscopic measurements, performed at O K-edge and Ni L-edge, reveal that NiO hybridization is increased after the initial irradiation. Charge-transfer multiplet calculations of the Ni L-edge indicate that variation of magnetic behaviour can be related to the NiO hybridization strength inducing a further variation in Ni spin state.

Energy based model for temperature dependent behavior of ferromagnetic materials

An energy based model for temperature dependent anhysteretic magnetization curves of ferromagnetic materials is proposed and benchmarked against experimental data. This is based on the calculation of macroscopic magnetic properties by performing an energy weighted average over all possible orientations of the magnetization vector. Most prior approaches that employ this method are unable to independently account for the effect of both inhomogeneity and temperature in performing the averaging necessary to model experimental data. Here we propose a way to account for both effects simultaneously and benchmark the model against experimental data from ~5K to ~300K for two different materials in both annealed (fewer inhomogeneities) and deformed (more inhomogeneities) samples. This demonstrates that this framework is well suited to simulate temperature dependent experimental magnetic behavior.

Nickel(II) Complex of a Hexadentate Ligand with Two o-Iminosemiquinonato(1-) π-Radical Units and Its Monocation and Dication.

Aerobic reaction of a hexadentate redox-active o-aminophenol-based ligand, H4L(3) = N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'-diamino(diphenyldithio)-ethane, in CH3OH with Ni(II)(O2CCH3)2·4H2O and Et3N afforded isolation of a reddish-brown crystalline solid [Ni(L(3))] 1. Cyclic voltammetry (CV) experiment exhibits two oxidative responses at E1/2 = 0.09 and 0.53 V vs SCE (saturated calomel electrode). Chemical oxidation of 1 in air by [Fe(III)(η(5)-C5H5)2][PF6] and AgBF4 in CH2Cl2 led to the isolation of one-electron oxidized species [1](1+) as purple [1][PF6]·CH2Cl2 and two-electron oxidized species [1](2+) as dark purple [1][BF4]2·CH2Cl2, respectively. X-ray crystallographic analysis at 100(2) K unambiguously established that the ligand is present in [Ni(II){(L(ISQ)O,N)(•-)}{(L(ISQ)O,N)(•-)}{(LS,S)(0)}] 1, [Ni(II){(L(IBQ)O,N)(0)}{(L(ISQ)O,N)(•-)}{(LS,S)(0)}][PF6]·CH2Cl2, and [Ni(II){(L(IBQ)O,N)(0)}{(L(IBQ)O,N)(0)}{(LS,S)(0)}][BF4]2·CH2Cl2, as monoanionic o-iminosemiquinonate(1-) π-radical (Srad = 1/2) (L(ISQ))(•-) and neutral o-iminoquinone (L(IBQ))(0) redox-levels. Complexes 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 possess an S = 2, 3/2, and 1 ground-state, respectively, established by temperature-dependent (2-300 K) magnetic behavior of 1 and [1][PF6]·CH2Cl2, and a μeff value of [1][BF4]2·CH2Cl2 at 300 K. Both 1 and [1][PF6]·CH2Cl2 exhibit ferromagnetic exchange-coupling between the two electrons of Ni(II) and two/one ligand π-radicals, respectively. The redox processes are shown to be ligand-based. Spectroscopic and redox properties, and density functional theory (DFT) calculations at the CAM-B3LYP-level of theory adequately describe the electronic structure of 1, [1](1+), and [1](2+). The observed UV-vis-NIR absorptions for 1, [1][PF6]·CH2Cl2, and [1][BF4]2·CH2Cl2 have been assigned, based on time-dependent (TD)-DFT calculations.