Sublattice Magnetization Research Articles

Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures.

Voltage control of magnetic order is desirable for spintronic device applications, but 180° magnetization switching is not straightforward because electric fields do not break time-reversal symmetry. Ferrimagnets are promising candidates for 180° switching owing to a multi-sublattice configuration with opposing magnetic moments of different magnitudes. In this study we used solid-state hydrogen gating to control the ferrimagnetic order in rare earth-transition metal thin films dynamically. Electric field-induced hydrogen loading/unloading in GdCo can shift the magnetic compensation temperature by more than 100 K, which enables control of the dominant magnetic sublattice. X-ray magnetic circular dichroism measurements and ab initio calculations indicate that the magnetization control originates from the weakening of antiferromagnetic exchange coupling that reduces the magnetization of Gd more than that of Co upon hydrogenation. We observed reversible, gate voltage-induced net magnetization switching and full 180° Néel vector reversal in the absence of external magnetic fields. Furthermore, we generated ferrimagnetic spin textures, such as chiral domain walls and skyrmions, in racetrack devices through hydrogen gating. With gating times as short as 50 μs and endurance of more than 10,000 cycles, our method provides a powerful means to tune ferrimagnetic spin textures and dynamics, with broad applicability in the rapidly emerging field of ferrimagnetic spintronics.

Tailoring magnetism in spinel vanadate CoV2O4 epitaxial thin films

Near itinerant cubic bulk CoV2O4 is at variance with other spinel vanadates by not showing orbital ordering down to low temperature, albeit it displays fragile anomalies related to spin, and lattice structure, signaling a spin/orbital glass transition around 95 K. We investigate tetragonal-like epitaxial CoV2O4 films on SrTiO3 and (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates that exhibit pronounced signature of spin reorientation transition from to a/b plane around 90 K unlike its bulk counterpart. Using in-plane and out-of-plane magnetic measurements, we demonstrate the intricate link between Co2+ and V3+ sublattice magnetizations that give rise to anisotropic magnetic switching. In-plane magnetic measurements reveal a wasp-waist shaped M(H) loop below reorientation transition temperature, while the out-of-plane follows antiferromagnet-like M(H) response. The wasp-waist shaped feature could be linked to in-plane spin-canted (anti)ferromagnetism induced by canting away of V-spins away from antiferromagnetically coupled Co-spin direction below reorientation transition temperature. Further, we uncover the evidence for slow relaxation over a period of ∼104 s at 20 K and memory effect that indicates the possible existence for magnetic glassy phase in the low temperature regime. Using epitaxial strain as a control knob, our results inspire future study to manipulate orbital states, spin texture and itinerant electron character in tailored CoV2O4 films away from cubic lattice symmetry.

Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2

Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe Mössbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. The coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.

Magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6

Iridium-based double perovskites having mixed 3d–5d–4f magnetic sub-lattices are expected to exhibit exotic magnetic phenomenon. In this paper, we report a study of structural, magnetic and transport properties of the mixed 3d–5d–4f double perovskite Sm2CoIrO6 (SMCO), which crystallizes in monoclinic structure with space group P21/n and the crystal symmetry remains same throughout the measured temperature down to 15 K. High resolution synchrotron x-ray diffraction reveals an isostructural phase transition around 104 K. Magnetization measurements on polycrystalline samples indicate that SMCO orders ferrimagnetically at T FiM = 104 K; while, a second transition is observed below 10 K due to the rare-earth (Sm3+) ordering. The ferrimagnetic transition is well-understood by Néel's two-sublattice model, which is primarily ascribed to antiferromagnetic coupling between Co2+ and Ir4+ sub-lattices. Electronic transport measurement shows the insulting behaviour of SMCO, which follows Mott variable-range hopping conduction mechanism. However, dielectric measurements as a function of temperature rules out the presence of magneto dielectric coupling in this compound.

Ab initio calculations, mean field approximation and Monte Carlo simulation of the electronic, magnetic and magnetocaloric properties of the double perovskite Ba2NiReO6

ABSTRACT The electronic, magnetic and magnetocaloric properties of double perovskite have been studied by using the Density Functional Theory, the Mean-Field Approximation and the Monte Carlo simulation. This material contains two magnetic sublattices where the first is occupied by the ions with the spin and the second is occupied by with the spin . Using the first principle calculations, it is found that the compound shows a half metallic behavior without Spin-Orbit Coupling (SOC) and a metallic one with SOC calculations. The total magnetic moment is determined and its value is equal to . The total magnetization, the total susceptibility, the magnetic entropy change, the adiabatic temperature change, the relative cooling power and the hysteresis phenomena of the compound have been investigated. From the obtained results, we can conclude that the compound is a good candidate for spintronic and magnetic refrigeration applications.

Magnetization dynamics of antiferromagnetic metals of PtMn and IrMn driven by a pulsed spin-transfer torque

Antiferromagnets are promising materials for memory devices owing to their ultrafast spin dynamics. For efficient control of antiferromagnets, a direct interaction between the spin current and local magnetization of the sublattice is required. In this study, we demonstrated that a short-pulsed spin current can induce fast dynamics of metallic antiferromagnets of PtMn and IrMn via spin-transfer torque on the magnetization of sublattices. We employed two methods to generate a short-pulsed spin current, namely ultrafast demagnetization of a ferromagnet and optical spin polarization of a heavy metal. The magnetization dynamics were measured using the time-resolved magneto-optical Kerr effect and were analyzed using the Landau–Lifshitz–Gilbert equation. Our results provide important evidence of the direct interaction between the magnetization of antiferromagnets and spin current.

Domain wall induced spin-polarized flat bands in antiferromagnetic topological insulators

A flat band in fermionic system is a dispersionless single-particle state with a diverging effective mass and nearly zero group velocity. These flat bands are expected to support exotic properties in the ground state, which might be important for a wide range of promising physical phenomena. For many applications it is highly desirable to have such states in Dirac materials, but so far they have been reported only in non-magnetic Dirac systems. In this work we propose a realization of topologically protected spin-polarized flat bands generated by domain walls in planar magnetic topological insulators. Using first-principles material design we suggest a family of intrinsic antiferromagnetic topological insulators with an in-plane sublattice magnetization and a high N\'eel temperature. Such systems can host domain walls in a natural manner. For these materials, we demonstrate the existence of spin-polarized flat bands in the vicinity of the Fermi level and discuss their properties and potential applications.

The magnetic properties and hysteresis loops of mixed spin-(3/2,2) hexagonal Ising nanowire system with alternate layers

In this paper, we have examined in detail the behavior of magnetic properties, hysteresis loops, and compensation phenomenon of a ferrimagnetic mixed spin-(3∕2,2) hexagonal Ising nanowire with alternate layers within the Monte Carlo method based on the Metropolis algorithm. The effect of longitudinal crystal field and exchange coupling constants on the total and the sublattice magnetizations, susceptibilities, specific heat, internal energy, as well as hysteresis loops are investigated for particular parameters. The obtained résults showed different interesting magnetic phenomena, such as seven and triple hysteresis loops at low temperatures, and one or double compensation temperatures under certain parameter values. Our outcomes are also compared with various experimental and theoretical studies.

Relationship between A-site cation and magnetic structure in 3d−5d−4f double perovskite iridates Ln2NiIrO6 ( Ln=La , Pr, Nd)

We report a comprehensive investigation of $L{n}_{2}{\mathrm{NiIrO}}_{6}$ ($Ln=\text{La}$, Pr, Nd) using thermodynamic and transport properties, neutron powder diffraction, resonant inelastic x-ray scattering, and density-functional theory (DFT) calculations to investigate the role of A-site cations on the magnetic interactions in this family of hybrid $3d\text{\ensuremath{-}}5d\text{\ensuremath{-}}4f$ compositions. Magnetic structure determination using neutron diffraction reveals antiferromagnetism for ${\mathrm{La}}_{2}{\mathrm{NiIrO}}_{6}$, a collinear ferrimagnetic Ni and Ir state that is driven to long-range antiferromagnetism upon the onset of Nd ordering in ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$, and a noncollinear ferrimagnetic Ni and Ir sublattice interpenetrated by a ferromagnetic Pr lattice for ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$. For ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$, heat-capacity results reveal the presence of two independent magnetic sublattices, and transport resistivity indicates insulating behavior and a conduction pathway that is thermally mediated. A first principles DFT calculation elucidates the existence of the two independent magnetic sublattices within ${\mathrm{Pr}}_{2}{\mathrm{NiIrO}}_{6}$ and offers insight into the behavior in ${\mathrm{La}}_{2}{\mathrm{NiIrO}}_{6}$ and ${\mathrm{Nd}}_{2}{\mathrm{NiIrO}}_{6}$. Resonant inelastic x-ray scattering is consistent with spin-orbit coupling splitting the ${t}_{2g}$ manifold of octahedral ${\mathrm{Ir}}^{4+}$ into a ${J}_{\mathrm{eff}}=\frac{1}{2}$ and ${J}_{\mathrm{eff}}=\frac{3}{2}$ state for all members of the series considered.

Strong influence of nonmagnetic ligands on the momentum-dependent spin splitting in antiferromagnets

Recent studies have shown that the non-relativistic antiferromagnetic ordering could generate momentum-dependent spin splitting analogous to the Rashba effect, but free from the requirement of relativistic spin-orbit coupling. Whereas the classification of such compounds can be illustrated by different spin-splitting prototypes (SSTs) from symmetry analysis and density functional theory calculations, the significant variation in bonding and structure of these diverse compounds representing different SSTs clouds the issue of how much of the variation in spin splitting can be traced back to the symmetry-defined characteristics, rather to the underlining chemical and structural diversity. The alternative model Hamiltonian approaches do not confront the issues of chemical and structural complexity, but often consider only the magnetic sublattice, dealing with the all-important effects of the non-magnetic ligands via renormalizing the interactions between the magnetic sites. To this end we constructed a 'DFT model Hamiltonian' that allows us to study SSTs at approximate 'constant chemistry', while retaining the realistic atomic scale structure including ligands. This is accomplished by using a single, universal magnetic skeletal lattice (Ni2+ ions in Rocksalt NiO) and designing small displacements of the non-magnetic (oxygen) sublattice which produce, by design, the different SSTs magnetic symmetries. We show that (i) even similar crystal structures having very similar band structures can lead to contrasting behavior of spin splitting vs. momentum, and (ii) even subtle deformations of the non-magnetic ligand sublattice could cause a giant spin splitting in AFM-induced SST. This is a paradigm shift relative to the convention of modeling magnets without considering the non-magnetic ligand that mediate indirect magnetic interaction (e.g., super exchange).

Magnetic and magneto-thermal properties of ferrimagnetic alloys (Er1−x Y x )(Co0.84Fe0.16)2 and their dependence on the orientations of resultant and sublattice magnetizations

In this paper structure, magnetic and magneto-thermal properties: magnetic entropy change (ΔS m) and refrigeration capacity (q) of Er1–x Y x (Co0.84Fe0.16)2 alloys (x = 0, 0.2, 0.4, 0.6, 0.8, 1) in magnetic fields up to 90 kOe in a temperature range of 5–360 K are investigated. An analysis of temperature dependences of magnetization (σ) and high-field susceptibility (χ hf) showed that in these compounds, three different ferri- and a one ferromagnetic structures are consequently realized. Concentration dependences of magnetic moment at 5 K (μ f.u.), Curie temperature (T C), residual magnetization (σ r) and coercivity (H c) have been shown to have an extreme at intermediate Y concentration. The character of temperature dependence of magnetic entropy change (ΔS m(T)) depends on the composition and originates from the type of magnetic structure of the compound and the mutual orientation of R- and 3d- element sublattices magnetization with respect to the resulting one. In compounds with x = 0.6 and x = 0.8 temperature regions with different signs of ΔS m are observed, reflecting the change of dominating R- or 3d- sublattice in the resulting magnetization.

High-Pressure Synthesis and Magnetic States of Magnetoplumbite Cobaltates CaCo12O19 and BaCo12O19.

Novel cobalt oxides, CaCo12O19 and BaCo12O19, have been synthesized under high-pressure and high-temperature conditions of 7 GPa and 1373 K, respectively. Rietveld refinement using synchrotron X-ray diffraction data indicates that the CaCo12O19 and BaCo12O19 crystallize in a magnetoplumbite structure with a hexagonal space group of P63/mmc (No. 194) as well as SrCo12O19. The magnetic study demonstrates that itinerant and localized 3d electrons coexist in all ACo12O19 (A = Ca, Sr, Ba) and the magnetic ground state transforms from antiferromagnetic (A = Ca) to ferrimagnetic (A = Sr) to antiferromagnetic (A = Ba), which is in stark contrast to the systematic change in the magnetoplumbite-related cobalt oxides of ACo6O11 from antiferromagnet (A = Ca) to ferrimagnet (A = Sr) to ferromagnet (A = Ba). The nonmonotonic magnetic evolution with isoelectronic A-site substitution in ACo12O19 is probably attributed to changes in the interactions between two magnetic sublattices of localized 3d electrons at trigonal-bipyramidal and tetrahedral sites for ACo12O19. This finding proposes the complex magnetic properties in the layered cobalt oxides with multiple magnetic sublattices in the coexistence system of itinerant and localized electrons.

Compensation and its systematics in spin-1/2 Ising trilayered triangular ferrimagnet

Trilayered, Ising, spin-1/2, ferrimagnets are interesting subjects for simulational studies for they show compensation effect. A Monte Carlo study on such a system with sublayers on a triangular lattice is performed in the current work. Three layers, making up the bulk, is formed completely by either A or B type of atoms. The interactions between like atoms (A-A; B-B) are ferromagnetic and between unlike atoms (A-B) are anti-ferromagnetic. Thus the system has three coupling constants and manifests into two distinct trilayer compositions: AAB and ABA. Metropolis single spin-flip algorithm is employed for the simulation and the location of the critical points (sublattice magnetisations vanish, leading to zero bulk magnetisation) and the compensation points (bulk magnetisation vanishes but nonzero sublattice magnetisations exist) are estimated. Close range simulations with variable lattice sizes for compensation point and Binder's cumulant crossing technique for critical points are employed for analysis and conditions for the existence of compensation points are determined. Comprehensive phase diagrams are obtained in the Hamiltonian parameter space and morphological studies at critical and compensation temperatures for both the configurations are also reported. The alternative description in terms of Inverse absolute of reduced residual magnetisation and Temperature interval between Critical and Compensation temperatures is also proposed and compared with traditional simulational results. Such simulational studies and the proposed systematics of compensation effect are useful in designing materials for specific technological applications.

Field tunable spin switching in perovskite YbFeO3 single crystal

We report the spin reorientation transition and spin switching transition in perovskite structure YbFeO3 single crystal. A spin reorientation transition of type Г4→Г2 occurs in the temperature range of 6 ∼ 8 K, and a type-Ⅱ spin switching along c-axis is found at temperature about 20 K under an applied magnetic field of 100 Oe. In field-cooled-cooling (FCC) process, due to the spin reversal of Yb3+ magnetic moments, the magnetic moments coupling of Yb3+ and Fe3+ change from parallel to antiparallel, which leads to a significant drop in magnetization at the transition temperature. Interestingly, the Magnetization vs. magnetic field curves at various temperatures above 8 K–200 K show magnetic field induced spin switching, for which the magnetization switches from negative/positive value to positive/negative value but without change of magnitude at a magnetic field induced spin switching point. The intriguing interaction between the two magnetic sublattices of rare earth (Yb3+) and iron (Fe3+) ions is controllable by the applied magnetic field to regulate the spin switching transition temperature in YbFeO3 single crystal and make it possible as one of low field potential materials for future application in spin devices.

Monte Carlo Simulation of a Mixed Spin‐1/2 and Spin‐3/2 Ising Ferrimagnetic System with Site Dilution

A study of the magnetic behavior of a mixed Ising system on a square lattice, where spins are located on alternating sites with spins , is presented. The change in the magnetic behavior of the system when empty sites are introduced in one of the sublattices or in both is analyzed. This system can be thought of as a site‐diluted ferrimagnet or as a system with nonmagnetic impurities. The Hamiltonian of the model contains an exchange interaction between nearest neighbors S–σ, next‐nearest‐neighbors , and a crystal field. The dependence of the total magnetization, the sublattice magnetizations, and the specific heat, with dilution is calculated. It is found that the behavior of the critical and compensation temperatures is strongly affected by dilution and where it is located. There is critical dilution, above which the compensation temperature disappears.

Electrical and thermal generation of spin currents by magnetic bilayer graphene.

Ultracompact spintronic devices greatly benefit from the implementation of two-dimensional materials that provide large spin polarization of charge current together with long-distance transfer of spin information. Here spin-transport measurements in bilayer graphene evidence a strong spin-charge coupling due to a large induced exchange interaction by the proximity of an interlayer antiferromagnet (CrSBr). This results in the direct detection of the spin polarization of conductivity (up to 14%) and a spin-dependent Seebeck effect in the magnetic graphene. The efficient electrical and thermal spin-current generation is the most technologically relevant aspect of magnetism in graphene, controlled here by the antiferromagnetic dynamics of CrSBr. The high sensitivity of spin transport in graphene to the magnetization of the outermost layer of the adjacent antiferromagnet, furthermore, enables the read-out of a single magnetic sublattice. The combination of gate-tunable spin-dependent conductivity and Seebeck coefficient with long-distance spin transport in a single two-dimensional material promises ultrathin magnetic memory and sensory devices based on magnetic graphene.

Ab-initio calculations combined with Monte Carlo simulation of the physical properties of Fe3S4 compound

The main objective of this paper is to evaluate the physical properties of Fe 3 S 4 material. To do so, Ab-initio calculations and Monte Carlo Simulations (MCS) by means of the mixed spin model have been used. Fe 3 S 4 compound is formed by two magnetic sub-lattices, one occupied the A tetrahedral with spin 5/2 and the other occupied by B octahedral with both spin 2 and 5/2. The density of states (DOS) has been investigated and confirmed that the compoundis a half metal. Further, the magnetization, susceptibility and specific heat curves have been determined for different sizes of the systemand fromwhich the values of critical exponentsand the critical temperature (T c ) have been calculated. Besides, the temperature-dependent magnetization for different values of crystal field has been analyzed to provide an insight into the relation compensation phenomena and crystal field effect.

Metamagnetic Behavior in a Quadruple Perovskite Oxide.

A cubic quadruple perovskite oxide CeMn3Cr4O12 has been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1273 K. The X-ray absorption spectroscopy reveals that the Ce ions are in a trivalent state, as represented by the ionic model of Ce3+Mn3+3Cr3+4O12. The magnetic study demonstrates three independent antiferromagnetic transitions attributed to Ce (∼10 K), Mn (46 K), and Cr (133 K) ions. Furthermore, a magnetic field-induced antiferromagnetic-to-ferromagnetic (metamagnetic) transition of Ce3+ 4f moments is observed at low temperatures below 20 K, exhibiting a rare example of metamagnetism in the Ce3+-oxides. This finding represents that the 3d-electron magnetic sublattices play a role in the metamagnetism of 4f-electron magnetic moments, demonstrating a new aspect of the 3d-4f complex electron systems.

Magnetic order of Dy3+ and Fe3+ moments in antiferromagnetic DyFeO3 probed by spin Hall magnetoresistance and spin Seebeck effect

We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) in single crystal of the rare-earth antiferromagnet DyFeO$_{3}$ with a thin Pt film contact. The angular shape and symmetry of the SMR at elevated temperatures reflect the antiferromagnetic order of the Fe$^{3+}$ moments as governed by the Zeeman energy, the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence of the signal on the magnetic field strength as evidence for field-induced order of the Dy$^{3+}$ moments up to room temperature. At and below the Morin temperature of 50$\,$K, the SMR monitors the spin-reorientation phase transition of Fe$^{3+}$ spins. Below 23$\,$K, additional features emerge that persist below 4$\,$K, the ordering temperature of the Dy$^{3+}$ magnetic sublattice. We conclude that the combination of SMR and SSE is a simple and efficient tool to study spin reorientation phase transitions and sublattice magnetizations.

Observation of novel charge ordering and spin reorientation in perovskite oxide PbFeO3

PbMO3 (M = 3d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6s and transition metal 3d orbitals. However, the detailed structure and physical properties of PbFeO3 remain unclear. Herein, we reveal that PbFeO3 crystallizes into an unusual 2ap × 6ap × 2ap orthorhombic perovskite super unit cell with space group Cmcm. The distinctive crystal construction and valence distribution of Pb2+0.5Pb4+0.5FeO3 lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb2+ and Pb4+) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a-axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b-axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe3+ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature.