Ferromagnetic Transition Research Articles

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

Spin-fluctuation theory of temperature-driven spin reorientations in ferromagnetic transition metal thin films

What will be the Euclidean dimension of an Ising ferromagnetic cubic shell?

The equilibrium and nonequilibrium properties of an Ising ferromagnetic cubic shell have been extensively studied by Monte Carlo simulation using Metropolis single spin flip algorithm. Although, geometrically the Euclidean dimension of the cubical shell is three, interestingly, the Ising ferromagnetic cubic shell undergoes ferromagnetic phase transition at a temperature which is very close to that for two-dimensional Ising ferromagnet. Surprisingly, the Ising ferromagnetic cubic shell shows a strange (neither exponential nor stretched exponential) kind of relaxation behaviour, instead of exponential relaxation as usually observed in the two dimensional Ising ferromagnet. The metastable lifetime of a ferromagnetic Ising cubical shell is studied as a function of the applied magnetic field. Here also, the cubic shell behaves more likely a two-dimensional object as found from statistical analysis and comparison with Becker-Döring prediction of classical nucleation theory.

Enhanced low field magnetocaloric effect through Fe doping induced ferromagnetic transition in HoCo0.8Fe0.2C compound

Enhanced low field magnetocaloric effect through Fe doping induced ferromagnetic transition in HoCo0.8Fe0.2C compound

Gallery of soft modes: Theory and experiment at a ferromagnetic quantum phase transition

Gallery of soft modes: Theory and experiment at a ferromagnetic quantum phase transition

Observation of Enhanced Long-Range Ferromagnetic Order in B-Site Ordered Double Perovskite Oxide Cd2CrSbO6.

A B-site ordered double perovskite oxide Cd2CrSbO6 was synthesized under high-pressure and high-temperature conditions. The compound crystallizes to a monoclinic structure with a space group of P21/n. The charge configuration is confirmed to be that of Cd2+/Cr3+/Sb5+. The magnetic Cr3+ ions form a tetrahedral structural frustrated lattice, while a long-range ferromagnetic phase transition is found to occur at TC = 16.5 K arising from the superexchange interaction via the Cr-O-Cd-O-Cr pathway. Electrical transport measurements indicate that Cd2CrSbO6 is an insulator that can be described by the Mott 3D variable range hopping mechanism. First-principles calculations reproduce well the ferromagnetic and insulating ground state of Cd2CrSbO6 with an energy band gap of 1.55 eV. The intrinsic ferromagnetic insulating nature qualifies Cd2CrSbO6 as a promising candidate for possible spintronics applications.

Abnormal Magnetic Phase Transition in Mixed-Phase (110)-Oriented FeRh Films on Al2O3 Substrates via the Anomalous Nernst Effect.

Iron rhodium (FeRh) undergoes a first-orderanti-ferromagnetic to ferromagnetic phase transition above its Curie temperature. By measuring the anomalous Nernst effect (ANE) in (110)-oriented FeRh films on Al2O3 substrates, the ANE thermopower over a temperature range of 100-350 K is observed, with similar magnetic transport behaviors observed for in-plane magnetization (IM) and out-of-plane magnetization (PM) configurations. The temperature-dependent magnetization-magnetic field strength (M-H) curves revealed that the ANE voltage is proportional to the magnetization of the material, but additional features magnetic textures not shown in the M-H curves remained intractable. In particular, a sign reversal occurred for the ANE thermopower signal near zero field in the mixed-magnetic-phase films at low temperatures, which is attributed to the diamagnetic properties of the Al2O3 substrate. Finite element method simulations associated with the Heisenberg spin model and Landau-Lifshitz-Gilbert equation strongly supported the abnormal heat transport behavior from the Al2O3 substrate during the experimentally observed magnetic phase transition for the IM and PM configurations. The results demonstrate that FeRh films on an Al2O3 substrate exhibit unusual behavior compared to other ferromagnetic materials, indicating their potential for use in novel applications associated with practical spintronics device design, neuromorphic computing, and magnetic memory.

Broad table-like magnetocaloric effect in the full hydrogen liquefaction range in Gd3Ni6XY

Gd3Ni6SiAl, Gd3Ni6SiGa, and Gd3Ni6AlGa (Ce3Ni6Si2-type, Im-3m, N 229, cI44) present a broad table-like magnetocaloric effect in the full hydrogen liquefaction range (20-77K) with a real plateau wide enough to be competitive for refrigeration devices based on the Ericsson cycle. The characterization of the magnetocaloric variables (|ΔSMpk|= 6.60J/kgK, TEC(10)= 6.44J/kgK for Gd3Ni6SiGa, |ΔSMpk|= 6.05J/kgK, TEC(10)= 6.01J/kgK for Gd3Ni6SiAl, all at μ0ΔH=5T) state that they are among the best of table-like magnetocaloric materials in this temperature range. The physical origin of this smooth and wide table-like effect is the combination of a spin reorientation transition (which appears in Gd3Ni6XY when Si or Ga is introduced) with the paramagnetic to ferromagnetic transition, close to each other. The application of the Banerjee criterion and the evolution of the critical exponent with temperature n(T) confirm that both transitions are second order, which is extremely relevant for real applications. From the study of the magnetic properties it has been inferred that the introduction of Si induces a magnetic ground state with combined ferromagnetic and antiferromagnetic components which turns to fully ferromagnetic at very low field. The critical exponents (β, γ, δ, n) have been found for the paramagnetic to ferromagnetic transitions; the values of γ (from 1.22 to 1.36) suggest that the magnetic interactions are short-range, though the ensembles do not correspond to any particular universality class.

Structure, Magnetic and Magnetocaloric Properties of Attempted P Substitutions in LaFe<sub>11.5</sub>Si<sub>1.5</sub> Giant Magnetocaloric Material

Recent theoretical and experimental studies suggested that P can enter the structure of La(Fe,Si)13 alloys and lead to a significant enhancement of the isothermal entropy change, one of the two main quantities characterizing the magnetocaloric effect. Here, we report a systematic study of P for Si substitutions in La(Fe,Si)13 alloys. Eight LaFe11.5Si1.5-xPx polycrystalline bulk samples with 0 ≤ x ≤ 0.2 were prepared by arc-melting followed by heat treatment. Powder x-ray diffraction and SEM/EDX analyses show that the α-Fe secondary phase progressively increases with the increase in P substitutions and that a La-rich LaP secondary phase appears. We therefore found that P does not actually enter the main La(Fe,Si)13 phase. Magnetization and DSC measurements confirm this interpretation as the Curie temperatures of La(Fe,Si,P)13 alloys are nearly insensitive to P for Si substitutions and the latent heat of the first-order ferromagnetic transition decreases with the increase in nominal P substitutions. Our work put into questions former reports of the literature on P addition in La(Fe,Si)13 and highlights the particularly complex synthesis of these alloys.

Antiferromagnetic to ferromagnetic phase transition as a transition to partial ordered spins. Application to La1−xCaxMnO3 in the doping range x ≥ 0.50

Magnetic state is a partial ordered state if only part of the electrons in the system give contribution to the magnetic order. We study Heisenberg model of two sublattice spin system, on the body-centered cubic lattice, with antiferromagnetic nearest neighbors exchange of sublattice A and B spins and two different ferromagnetic exchange constants for sublattice A (JA) and B (JB) spins. When JA>JB the system undergoes transition from paramagnetism to ferromagnetism at Curie temperature TC. Only the sublattice A spins give contribution to the magnetization of the system. Upon cooling, the system possesses ferromagnetism to antiferromagnetism transition at Néel temperature TN<TC. Below TN sublattice A and B electrons give contribution to the magnetization. The transition is a partial ordered transition. There is thermodynamic evidence for this transition in the magnetic specific heat of the system. As a function of temperature there are two maxima. At high temperature TC it is λ-type. At lower temperature TN it characterizes the transition from ferromagnetism to antiferromagnetism. As an example of ferromagnetism to antiferromagnetism partial ordered transition we consider the material La1−xCaxMnO3 in the doping range x≥0.50. Our calculations reproduce the experimental magnetization-temperature curve.

Magnetotransport and angle-resolved photoemission spectroscopy of MnSb12Te19: a new member of MnSb2nTe3n+1 family

The quest for intrinsically ferromagnetic topological materials is a focal point in the study of topological phases of matter, as intrinsic ferromagnetism plays a vital role in realizing exotic properties such as the anomalous Hall effect (AHE) in quasi-two-dimensional materials, and this stands out as one of the most pressing concerns within the field. Here, we investigate a novel higher order member of the MnSb2nTe3n+1family, MnSb12Te19, for the first time combining magnetotransport and angle-resolved photoemission spectroscopy (ARPES) measurements. Our magnetic susceptibility experiments identify ferromagnetic transitions at temperatureTc= 18.7 K, consistent with our heat capacity measurements (T= 18.8 K). The AHE is observed for the field along thec-axis belowTc. Our study of Shubinikov-de-Haas oscillations provides evidence for Dirac fermions withπBerry phase. Our comprehensive investigation reveals that MnSb12Te19exhibits a FM ground state along with AHE, and hole-dominated transport properties consistent with ARPES measurements.

In-plane anisotropic magnetoresistance and planar Hall effect in off-stoichiometric single crystal Mn3Ga

We report the observation of in-plane anisotropic magnetoresistance (AMR) and planar Hall effect in our recently discovered kagome antiferromagnetic off-stoichiometric single crystal of Mn3Ga. We found that the in-plane AMR is dominated by a sixfold symmetry at low temperature due to the kagome lattice magnetocrystalline anisotropy. However, an unusual fourfold symmetry is also revealed by the angular-dependent AMR measurements, which originates from the little distortion of the crystal accompanying the slight ferromagnetic transition. Moreover, we also found a clear planar Hall effect signal in off-stoichiometric single crystal of Mn3Ga, which may be related to the chiral anomaly, one of the signatures of the magnetic Weyl fermions.

One-step ultrafast Joule heating synthesis of EuB6 ceramics and their electronic transport and magnetic properties

The synthesis of high-performance rare-earth borides (e.g., RB2, RB4, R2B5, RB6, RB12, and RB66) typically necessitates sintering at high temperatures and high pressures for prolonged durations. Traditional methods, such as hot-pressing sintering and spark plasma sintering, are marked by high production costs and low efficiency. Here, using EuB6 as an example, we demonstrate the successful synthesis of rare-earth boride ceramics utilizing the one-step ultrafast joule heating technology. Using this method, we optimized the sintering temperature and duration and synthesized EuB6 ceramics with superior electronic and magnetic properties at 1600 °C in just 5 min. The EuB6 ceramics prepared under optimized conditions show distinct paramagnetic to ferromagnetic phase transition, significant negative magnetoresistance, and enhanced magnetization. The combination of the one-step ultrafast Joule heating technology and boron thermal reduction method offers a simple and fast synthesis approach for fabricating polycrystalline EuB6 and may be extended to prepare other rare-earth and transition-metal borides.

Pseudospin Quantum Hall Ferromagnetism Probed by Electron Spin Resonance.

We study the effect of the pseudospin ferromagnetism with the aid of an electrically detected electron spin resonance in a wide AlAs quantum well containing a high quality two-dimensional electron system. Here, pseudospin emerges as a two-component degree of freedom, that labels degenerate energy minima in momentum space populated by electrons. The built-in mechanical strain in the sample studied imposes a finite "Zeeman" splitting between the pseudospin "up" and "down" states. Because of the anisotropy of the electron spin splitting we were able to independently measure the electron spin resonances originating from the two in-plane valleys. By analyzing the relative resonance amplitudes, we were able to investigate the ferromagnetic phase transitions taking place at integer filling factors of the quantum Hall effect when the magnetic field is tilted. The pseudospin nature of these transitions is demonstrated.

Oxygen Ion Pumping across Atomically Designed Oxide Heterointerfaces

AbstractComplex oxide heterointerfaces and heterostructures have demonstrated enormous emergent phenomena over the last decades, attributed to the reconstructions of mis‐matched crystalline structure, polarity, and spin ordering across the heterointerfaces. This work employs the heterostructures of La0.7Sr0.3MnO3 and CaFeO2.5 as model system to demonstrate an interface‐specific oxygen migration/reconstruction across the interfaces due to the mismatched chemical potential, which dramatically influences the ferromagnetic and electronic states of La0.7Sr0.3MnO3 layer. Specifically, the alternative stacking of octahedral (Oh) and tetrahedral (Td) layers in CaFeO2.5 are used to form two distinct heterointerfaces, namely the Oh‐Td and the Oh‐Oh interfaces with the adjacent La0.7Sr0.3MnO3 layer. Interestingly, the oxygen ion migrates toward opposite directions across the interface for these two cases, in which the CaFeO2.5 layer acts as an “oxygen pump” and manipulates the oxygen contents of its adjacent La0.7Sr0.3MnO3 layers. Such manipulation leads to a dramatically changed ferromagnetic transition temperature for the heterostructure with the Oh‐Td and Oh‐Oh interface. This work establishes a feasible and efficient strategy to control the oxygen ionic distribution through atomic‐scale interface design and opens up new opportunities to exploit emergent states at the complex oxide heterostructures through selective oxygen ion evolution.

Intrinsic single-layer multiferroics in transition-metal-decorated chromium trihalides

Two-dimensional materials possessing intrinsic multiferroic properties have long been sought to harness the magnetoelectric coupling in nanoelectronic devices. Here, we report the achievement of robust type I multiferroic order in single-layer chromium trihalides by decorating transition metal atoms. The out-of-plane ferroelectric polarization exhibits strong atomic selectivity, where 12 of 84 single-layer transition metal-based multiferroic materials possess out-of-plane ferroelectric or antiferroelectric polarization. Group theory reveals that this phenomenon is strongly dependent on p–d coupling and crystal field splitting. Cu decoration enhances the intrinsic ferromagnetism of trihalides and increases the ferromagnetic transition temperature. Moreover, both ferroelectric and antiferroelectric phases are obtained, providing opportunities for electrical control of magnetism and energy storage and conversion applications. Furthermore, the transport properties of Cu(CrBr3)2 devices are calculated based on the non-equilibrium Green’s function, and the results demonstrate outstanding spin-filtering properties and a low-bias negative differential resistance (NDR) effect for low power consumption.

FenB2+2n (n = 1, 2), an intrinsic room temperature ferromagnetic MBene with significant magnetic performance enhancement achievable by carbon substitution

From spintronics to data storage technology, two-dimensional (2D) ferromagnetic materials show great promise for various applications. This work reports a series of stable ferromagnetic transition metal boride FenB2+2n (n = 1, 2), where robust long-range ferromagnetic exchange coupling and large perpendicular magnetic anisotropy energy (MAE) allow the ferromagnetic transition temperature (Tc) of the FenB2+2n monolayer to reach above room temperature. The metallic FenB2+2n exhibits n- and p-type Dirac transport in both spin channels with a high Fermi velocity. Furthermore, the application of biaxial compressive strain and electron doping can greatly increase the ferromagnetic coupling and MAE of FeB4 monolayers. On this basis, the FeB2C2 alloy with a high concentration of carbon substitution has been designed, which allows the nonvolatile integration of in-plane compressive strain and electron doping. As expected, this substitution doping resulted in a significant increase in the Tc and MAE of the system. Our findings provide perspectives for the study of 2D magnetic materials.

Non-Fermi-liquid behavior consistent with a preasymptotic disorder-tuned ferromagnetic quantum critical point in the heavy fermion system CeTi1−xVxGe3

An investigation of the thermodynamic and electrical transport properties of the isoelectronic chemical substitution series CeTi1−xVxGe3 (CTVG) single crystals is reported. As x increases, the ferromagnetic (FM) transition temperature is suppressed, reaching absolute zero at the critical concentration x=0.4, where a non-Fermi-liquid low-temperature specific heat and electrical resistivity, as well as the hyperscaling of specific heat and magnetization, are found. Our study suggests the presence of an FM quantum critical point (QCP) in CTVG. The obtained critical exponents indicate that CTVG falls in the preasymptotic region of the disorder-tuned FM QCP predicted by the Belitz-Kirkpatrick-Vojta theory. Published by the American Physical Society 2024

Magnetometry in a diamond anvil cell using nitrogen vacancy centers in a nanodiamond ensemble.

The emerging field of optical magnetometry utilizing negative-charged nitrogen vacancy (NV-) centers provides a highly sensitive lab bench technique for spatially resolved physical property measurements. Their implementation in high pressure diamond anvil cell (DAC) environments will become common as other techniques are often limited due to the spatial constraints of the sample chamber. Apparatus and techniques are described here permitting for more general use of magnetic field measurements inside a DAC using continuous wave optical detected magnetic resonance in NV- centers in a layer of nanodiamonds. A microstrip antenna delivers a uniform microwave field to the DAC and is compatible with simple metal gaskets, and the sensor layer of deposited nanodiamonds allows for simple determination of the magnetic field magnitude for B in the 1-100G range. The ferromagnetic transition in iron at 18GPa is measured with the apparatus, along with its hysteretic response.

Enhanced magnetocaloric and cold storage properties in HoCu2-xNix (x=0.05–0.5) compounds for hydrogen liquefaction

Based on first-principle calculations and experiments, the electronic structure, magnetism, magnetocaloric effect and cold storage properties of HoCu2-xNix (x=0.05–0.5) compounds have been investigated. The theoretical calculations revealed that the magnetic interactions of the HoCu2-xNix compounds were gradually transformed to ferromagnetic states when the Ni element was added above 0.0625. In addition, the Ni element leads to a decreasing Fermi energy level, which results in a significant enhancement of orbital hybridization around the Fermi surface, which may be responsible for the magnetic jump. The magnetic phase transition temperatures of the HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds are 14.4 K and 26.0 K, respectively. The ferromagnetic state transition is responsible for the excellent magnetocaloric effect of the HoCu2-xNix compounds under low magnetic fields. The maximum magnetic entropy changes of the HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds were 14.7 J/kg K and 11.5 J/kg under varying magnetic fields from 0 to 2 T. In addition, the Ni element make the HoCu2 compound exhibit more excellent cold storage capability. The peak of specific heat capacities of HoCu1.75Ni0.25 and HoCu1.5Ni0.5 compounds were 0.6 J/cm−3K−1 and 0.9 J/cm−3K−1 under 0 T. The present results indicate that HoCu2-xNix (x=0.05–0.5) compounds have promising applications in cryogenic cold storage and magnetic refrigeration.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.