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We review the most significant results obtained in the framework of the microscopic approach to a systematic study of magnetic dynamics in two-dimensional ferromagnetic and antiferromagnetic materials with a strong Rashba spin-orbit coupling. For model systems, we discuss the microscopic derivation of the Gilbert damping tensor, spin-orbit and spin-transfer torques, and symmetric and antisymmetric exchange interactions. It is shown that in both antiferromagnetic and ferromagnetic systems, the presence of a sufficiently strong spin-orbit coupling leads to an anisotropy of spin torques and Gilbert damping. We focus on an analysis of spin-orbit torques in a two-dimensional Rashba antiferromagnet. We also address the possibility of switching the antiferromagnetic order parameter via short current pulses in the plane of the sample.

In this manuscript, we investigate a new technique to describe the tangent, principal normal, and binormal osculating magnetic and electric flow density in the normal direction in the ordinary space. Based on the computed flow density, we determine the Frenet-Serret vectors of the osculating magnetic and electric flow phase in the normal phase. Then, we consider the modified visco Heisenberg ferromagnetic model to observe the variation when we compare Frenet-Serret vectors of the osculating magnetic and electric flow phase due to the modified visco Heisenberg ferromagnetic. Finally, we determine the existence conditions for describing the field vectors flux surfaces under the osculating evolution equations in the normal direction.

Control on the size of copper oxide (CuO) in the nano range is a highly motivating approach to study its multifunctional nature. The present investigation reports a sol-gel derived Ni doped CuO nanoparticles (Cu1-xNixO). Rietveld refinement of the XRD spectra confirms the formation of single monoclinic phase of Cu1-xNixO nanoparticles having crystallite size within the range of 19–21 nm. Raman spectra show the presence of characteristics Raman active modes and vibrational bands in the Cu1-xNixO samples that corroborate the monoclinic phase of the samples as revealed by refinement of XRD data. The estimated band gap of pure CuO is found to be ∼1.43 eV, which decreases with the increase of dopant concentration into CuO matrix. This result is in line with estimated crystallite size. Magnetization curves confirm the weak ferromagnetic nature of Cu1-xNixO nanoparticles which reveal the DMS phase. This weak magnetic nature may be induced in the samples due to the exchange interaction between the localized magnetic d-spins of Ni ions and carriers (holes or electrons) from the valence band of pristine CuO lattice. Replacement of Cu+2 by Ni+2 ions into the host CuO lattice induces the magnetization. The quantified value of squareness ratio (S

This article introduces and develop a new area of transparent conducting material by doping GaN with two rare earth (RE) impurities (Eu, Sm). Our theoretical calculations confirm that the co-doped compound exhibits half-metallic ferromagnet (HMF) with 100% spin polarization at the Fermi level using GGA and mBJ. To determine which magnetic configuration is the most stable one, we compared the energy of ferromagnetic and antiferromagnetic states. Our results suggest that the ferromagnetic state is the most stable ground state. The exchange splitting energy and exchange constants $$N_{0} \alpha$$ and $$N_{0} \beta$$ are calculated. Additionally, we determined the electron specific heat ‘c’. It has a high optical transmittance and conductivity. These properties make GaN doped with double rare-earth impurities a potential material in optoelectronic and solar cell applications. For the calculations of mechanical, optical, and transport properties, the generalized gradient approximation + Hubbard U (GGA + U) and the modified Becke–Johnson (GGA-TB-mBJ) approximations were used.

Fundamental symmetry breaking and relativistic spin–orbit coupling give rise to fascinating phenomena in quantum materials. Of particular interest are the interfaces between ferromagnets and common s-wave superconductors, where the emergent spin-orbit fields support elusive spin-triplet superconductivity, crucial for superconducting spintronics and topologically-protected Majorana bound states. Here, we report the observation of large magnetoresistances at the interface between a quasi-two-dimensional van der Waals ferromagnet Fe0.29TaS2 and a conventional s-wave superconductor NbN, which provides the possible experimental evidence for the spin-triplet Andreev reflection and induced spin-triplet superconductivity at ferromagnet/superconductor interface arising from Rashba spin-orbit coupling. The temperature, voltage, and interfacial barrier dependences of the magnetoresistance further support the induced spin-triplet superconductivity and spin-triplet Andreev reflection. This discovery, together with the impressive advances in two-dimensional van der Waals ferromagnets, opens an important opportunity to design and probe superconducting interfaces with exotic properties., The interfaces between ferromagnets and superconductors receive many attentions due to emergent relativistic spin-orbit coupling. Here, the authors provide possible evidence for spin triplet Andreev reflection at the interface between a van der Waals ferromagnet Fe0.29TaS2 and a s-wave superconductor NbN.

Coexistence of nonvolatile unipolar and volatile threshold resistive switching is observed in the Pt/LaMnO3 (LMO)/Pt heterostructures. The nonvolatile unipolar memory is achieved by applying a negative bias, while the volatile threshold resistive switching is obtained under a positive bias. Additionally, the pristine low resistance state (LRS) could be switched to high resistance state (HRS) by the positive voltage sweeping, which is attributed to the conduction mechanism of Schottky emission. Subsequently, the insulator-to-metal transition in the LMO film due to formation of ferromagnetic metallic phase domain contributes to the volatile threshold resistive switching. However, the nonvolatile unipolar switching under the negative bias is ascribed to the formation/rupture of oxygen-vacancy conducting filaments. The simultaneously controllable transition between nonvolatile and volatile resistance switching by the polarity of the applied voltage exhibits great significance in the applications of in-memory computing technology.

Superconductor-ferromagnet interfaces in two-dimensional heterostructures present a unique opportunity to study the interplay between superconductivity and ferromagnetism. The realization of such nanoscale heterostructures in van der Waals (vdW) crystals remains largely unexplored due to the challenge of making atomically-sharp interfaces from their layered structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by inserting a few-layer ferromagnetic insulator Cr2Ge2Te6 into two layers of superconductor NbSe2. The critical current and corresponding junction resistance exhibit a hysteretic and oscillatory behavior against in-plane magnetic fields, manifesting itself as a strong Josephson coupling state. Also, we observe a central minimum of critical current in some JJ devices as well as a nontrivial phase shift in SQUID structures, evidencing the coexistence of 0 and π phase in the junction region. Our study paves the way to exploring sensitive probes of weak magnetism and multifunctional building-blocks for phase-related superconducting circuits using vdW heterostructures., The superconductor-ferromagnet interface provides a unique opportunity to study the interplay between superconductivity and ferromagnetism. Here, the authors build a van der Waals ferromagnetic Josephson junction evidencing a strong 0 and π phase Josephson coupling.

The antiperovskite ZnFe3N is studied by using density functional theory calculations and Monte Carlo simulation. Based on the electronic and magnetic properties, it is found that ZnFe3N behaves as a ferromagnetic metallic material. The exchange interactions and the magnetic anisotropy, defined as the Hamiltonian parameters of the studied system, are calculated and used in the Monte Carlo study. The second order transition at a Curie temperature Tc = 760K, reviled experimentally in a previous work, has been confirmed. The magnetic entropy change and the relative cooling power, under various applied magnetic fields are analyzed in order to evaluate the magnetocaloric effect of ZnFe3N. The results suggest that ZnFe3N is a good candidate for the magnetic refrigeration applications.

The quanta of magnetic excitations - magnons - are known for their unique ability to undergo Bose-Einstein condensation at room temperature. This fascinating phenomenon reveals itself as a spontaneous formation of a macroscopic coherent state under the influence of incoherent stimuli. Spin currents have been predicted to offer electronic control of magnon Bose-Einstein condensates, but this phenomenon has not been experimentally evidenced up to now. Here we experimentally show that current-driven Bose-Einstein condensation can be achieved in nanometer-thick films of magnetic insulators with tailored dynamic magnetic nonlinearities and minimized magnon-magnon interactions. We demonstrate that, above a certain threshold, magnons injected by the spin current overpopulate the lowest-energy level forming a highly coherent spatially extended state. By accessing magnons with essentially different energies, we quantify the chemical potential of the driven magnon gas and show that, at the critical current, it reaches the energy of the lowest magnon level. Our results pave the way for implementation of integrated microscopic quantum magnonic and spintronic devices., Comment: This is a preprint of an article published in Nature Communications. The final authenticated version is available online at: https://doi.org/10.1038/s41467-021-26790-y

Out-of-plane spin polarization {\sigma}_z has attracted increasing interests of researchers recently, due to its potential in high-density and low-power spintronic devices. Noncollinear antiferromagnet (AFM), which has unique 120{\deg} triangular spin configuration, has been discovered to possess {\sigma}_z. However, the physical origin of {\sigma}_z in noncollinear AFM is still not clear, and the external magnetic field-free switching of perpendicular magnetic layer using the corresponding {\sigma}_z has not been reported yet. Here, we use the cluster magnetic octupole in antiperovskite AFM Mn3SnN to demonstrate the generation of {\sigma}_z. {\sigma}_z is induced by the precession of carrier spins when currents flow through the cluster magnetic octupole, which also relies on the direction of the cluster magnetic octupole in conjunction with the applied current. With the aid of {\sigma}_z, current induced spin-orbit torque (SOT) switching of adjacent perpendicular ferromagnet is realized without external magnetic field. Our findings present a new perspective to the generation of out-of-plane spin polarizations via noncollinear AFM spin structure, and provide a potential path to realize ultrafast high-density applications., Comment: 23 pages, 4 figures, accepted by Nat. Commun

Ferromagnetism in two-dimensional materials presents a promising platform for the development of ultrathin spintronic devices with advanced functionalities. Recently discovered ferromagnetic van der Waals crystals such as CrI3, readily isolated two-dimensional crystals, are highly tunable through external fields or structural modifications. However, there remains a challenge because of material instability under air exposure. Here, we report the observation of an air-stable and layer-dependent ferromagnetic (FM) van der Waals crystal, CrPS4, using magneto-optic Kerr effect microscopy. In contrast to the antiferromagnetic (AFM) bulk, the FM out-of-plane spin orientation is found in the monolayer crystal. Furthermore, alternating AFM and FM properties observed in even and odd layers suggest robust antiferromagnetic exchange interactions between layers. The observed ferromagnetism in these crystals remains resilient even after the air exposure of about a day, providing possibilities for the practical applications of van der Waals spintronics.

According to the first principles, the WIEN2k program based on density functional theory (DFT) calculations is utilized to investigate the structural, magnetic, electronic, and optical properties of rare-earth vanadate perovskites PrVO3 (PVO) and NdVO3 (NVO). All calculations were performed by utilizing the full-potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA) under the potentials PBE-GGA, PBEsol-GGA, and WC-GGA. The optimized results show that the two compounds PVO, and NVO crystallize in a cubic structure with (Pm-3m) space group (No. 221) and lattice constants of (a = 3.8100 –3.8900 A). Partial and total spin magnetic moments confirm the ferromagnetic (FM) nature of these compounds, and the major part of their total magnetic moments (MCell ≈ 4.0 and ≈ 5.0 μB) is contributed by V3+ ions through the FM 3d-2p exchange interaction V3+↑–O2−↓–V4+↑ within the ground-state energies. The calculated spin-polarized electronic band structures, density of states, and charge density indicate that PVO and NVO exhibit a half-metallic property for all three GGA potentials. It is found that PBE-GGA gives reasonable results consistent with the previous data. Also, the main optical features are calculated and discussed to complete the description of the distinctive physical properties of these materials.

We have investigated the structural, optical and magnetic properties of Zn0.90Co0.10O, synthesized by the method of two electrode electrodeposition. X-ray diffraction measurement confirms the evolution of a single-phase polycrystalline hcp Wurtzite structure. Co-2p core-level XPS confirms that Co is present in mixed 2+ and 3+ states. The Fourier Transform Infrared (FTIR) spectrum findings substantiate the fact that a single-phase Hexagonal Wurtzite ZnO Crystal Structure has evolved. The SEM micrograph of the sample reveals smooth and dispersed morphology consisting of fine particles. The U-V visible NIR and PL spectroscopy measurements substantiate the fact that Co2+ has substituted Zn2+ in the matrix of ZnO which agrees with XRD findings. The sample shows good optical property and reveals a blue shift. It seems that the material is a potential candidate to be used as UV sensors. Room Temperature Intrinsic Ferromagnetism has been confirmed by VSM measurement.

In this work, α-phase Fe-12 V alloy (at.%) with high total magnetostriction is selected to perform Mossbauer and Vibrating Sample Magnetometer (VSM) measurements to investigate the temperature dependence of atomic clusters and the magnetic properties. The results show that with increasing temperature, the ferromagnetism firstly drops and then slightly increases, and finally decreases severely, which is mainly determined by the variations of the three kinds of atomic clusters (Fe-rich, V-rich and free-Fe) in the alloy. The hyperfine magnetic field, which decreases with temperature, is always dominated by the Fe-rich clusters. The atomic combination of the free-Fe clusters also determines the magnetic properties in the temperature range from room temperature to 600 °C; however, the free-Fe clusters contribution to the hyperfine magnetic fields tends to become zero above 600 °C, whereas that of the V-rich becomes obvious. When the temperature is high enough, the hyperfine magnetic field decreases sharply due to the destruction of the ordered Fe-rich state. VSM was selected to understand the relationship between the magnetic moment and the heating temperature, and the Curie temperature (TC=836.36 °C) of the Fe-12 V alloy was obtained as well. Finally, the formula reflecting the magnetic moment of the α-phase Fe-12 V alloy varying with temperature is also successfully derived.

We investigate the surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2, a material widely utilized for spintronic applications. While known for its relative air-insensitivity, exposure to air during the handling process (e.g. device or heterostructure fabrication) can lead to reduction or disappearance of its magnetic signal. Comparison of x-ray absorption and x-ray magnetic circular dichroism spectra between pristine and air-exposed Fe3-xGeTe2 confirm a naturally oxidized surface layer on the material. The surface oxide layer has predominantly Fe3+ content. X-ray absorption spectroscopy done on micron-sized exfoliated Fe3-xGeTe2 flakes reveal that the change in the surface chemical properties can be quite significant for thin flakes. The surface modulation of Fe3-xGeTe2 can lead to inaccuracies in characterizing its interfacial magnetic and spin transport properties, and complicate device and heterostructure fabrication processes.

We present a theoretical investigation on wave-vector filtering (WVF) effect for electrons in an antiparallel asymmetric double δ-magnetic-barrier nanostructure, which can be realized experimentally by patterning two asymmetric ferromagnetic (FM) stripes on top and bottom of GaAs/AlxGa1-xAs heterostructure, respectively. It is shown that a considerable WVF effect appears due to an essentially two-dimensional (2D) process for electrons across this nanostructure. It is also shown that WVF efficiency is associated with incident energy, incident direction and structural parameters. In particular, WVF efficiency can be tuned by applying a negative voltage, which maybe results in an electrically-controllable electron-momentum filter for nanoelectronics device applications.

High frequency permittivity of Fe-based nanocrystalline flakes (Fe-Cu-Nb-Si-B) being milled for different hours have been studied. An inverse dependence of peak frequency on the static dielectric constant in dielectric loss spectra is found. The total dielectric loss also increases with milling time. The Havriliak-Negami model is used to study the permittivity dispersion behaviors. It reveals that both the symmetric and asymmetric broadening factors play roles in the deviation of the measured permittivity spectra from the Debye-type theoretical dispersion. The fundamental physics for the dispersion of permittivity is “Maxwell-Wagner-Sillars” interfacial polarization, which arises from the difference in the conductivity of two phases existing in the nanostructures of flakes.

In this work, we studied the magnetic properties of a regularly tetrahedral molecule made of four spin-½, interconnected by exchange. For this purpose, we used the Heisenberg model and performed an exact resolution. In the case of a ferromagnetic coupling among the spins, the system orders itself under a magnetic field without displaying any net spontaneous magnetization. It behaves as a high spin-2 unique magnet. Under antiferromagnetic exchange, some exotic behaviour has been revealed due to the frustration governing the spin edifice. Thus, the magnetization is quantized into plateaus, which are separated by quantum phase transitions. In particular, we have argued the possibility of a quantum spin liquid (QSL) state that can occur at low temperature. This contribution intends mainly to bring single-molecular magnets to the front line of innovative nanoscale applications.

In order to study the magnetic properties of a ferromagnetic mixed spin, on the nanolayered structures described by spin-1/2 Ising model and spin-1 Blume-Capel model, analytical and numerical results were carried out through the mean field theory and computational simulation. The mean field approximation improved with the Gibbs–Bogoliubov inequality was used in association with Monte Carlo simulation to interpret the magnetic behavior of mixed spin lattices with hexagonal cylindrical symmetry. The Gibbs free energy, magnetization and critical frontiers were obtained. Besides the stable branches of the order parameters, there were obtained the metastable and unstable parts of these curves and also found the phase transitions of the metastable and unstable branches of the order parameters. The classifications of the stable, metastable and unstable states were made by comparing the free energy values of these states. The presence of a metastable transition, identified by the Ehrenfest classification as a second-order phase transition, involving an unstable state with order parameter nonzero and the highest entropy value, was adopted as the justification for an uncommon increase in the magnetization with the temperature. Beyond it, a weak ferromagnetic order in a midland chain of Ising spins in the cylindrical nanostructure was interpreted by curves of the order parameter and magnetic susceptibility.

Two-dimensional (2D) Van der Waals ferromagnets carry the promise of ultimately miniature spintronics and information storage devices. Among the newly discovered 2D ferromagnets all inherit the magnetic ordering from their bulk ancestors. Here we report a new 2D ferromagnetic semiconductor at room temperature, 2H phase vanadium diselenide (VSe2) which show ferromagnetic at 2D form only. This unique 2D ferromagnetic semiconductor manifests an enhanced magnetic ordering owing to structural anisotropy at 2D limit.

Ab initio study of the electronic and magnetic properties of vanadium-doped and vacancy-defected chalcopyrite semiconductor ZnSnAs2 was carried out using density functional theory within the spin generalized gradient approximation with Hubbard-like correction (SGGA + U). Investigation of magnetic properties shows that adding a transition element contributes to the magnetization of ZnSnAs2. The total energy calculations for a number of supercells show that a ferromagnetic spin ordering is favorable when V replaces Zn. The ferromagnetic alignment in V-doped ZnSnAs2 systems behaves half-metallic state. The presence of a single Zn- or Sn- or As-vacancy affects the ferromagnetism and may even strengthen the magnetization of V-doped ZnSnAs2.

A brief review of alternative phenomenological approaches to the spin dynamics of antiferromagnets are discussed in virtue of modern interest to ultrafast spin dynamics and it application. Specific properties of antiferromagnets, first of all, the possibility of spin dynamics faster then for ferromagnets are described. Novel types of solitons for anisotropic antiferromagnets are discussed.

Strain engineering of complex oxide heterostructures has provided routes to explore the influence of the local perturbations to the physical properties of the material. Due to the challenge of disentangling intrinsic and extrinsic effects at oxide interfaces, the combined effects of epitaxial strain and charge transfer mechanisms have been rarely studied. Here, we reveal the local charge distribution in manganite slabs by means of high-resolution electron microscopy and spectroscopy via investigating how the strain locally alters the electronic and magnetic properties of La0.5Sr0.5MnO3–La2CuO4 heterostructures. The charge rearrangement results in two different magnetic phases: an interfacial ferromagnetically reduced layer and an enhanced ferromagnetic metallic region away from the interfaces. Further, the magnitude of the charge redistribution can be controlled via epitaxial strain, which further influences the macroscopic physical properties in a way opposed to strain effects reported on single-phase films. Our work highlights the important role played by epitaxial strain in determining the spatial distribution of microscopic charge and spin interactions in manganites and provides a different perspective for engineering interface properties.

Spin-orbit torques (SOTs) have been investigated most widely in normal metal/ferromagnet bilayers where the spin Hall effect of normal metal is a main source of spin currents. Recently, ferromagnets are found to also serve as spin-current sources through spin-orbit coupling. In this work, we theoretically investigate SOT acting on ferromagnet2 in ferromagnet1/normal metal/ferromagnet2 trilayers, which is caused by the spin Hall and spin swapping effects of ferromagnet1. Our result provides an analytical expression of SOT in the trilayers, which may be useful for quantifying the spin Hall and spin swapping effects of ferromagnets and also for designing and interpreting SOT experiments where a ferromagnet is used as a spin-current source instead of a normal metal.

Results are presented from an analysis of the nano- and magnetic domain structures of high coercive Sm(CoCuFe)5 alloy using fractal geometry. Fractal dimension Df of the nano- and domain structures are determined at different stages of heat treatment. It is shown that Df ~ 2.08 corresponds to the nanostructure of samples with a coercive force of 7 kOe, while Df ~ 2.3 corresponds to the nanostructure of samples with a coercive force of 32 kOe.

In the framework of the classical equations for the magnetization dynamics and the collective variables approximation, the dynamics of magnetic vortices in two-dimensional ferromagnets with the easy-plane anisotropy and spatially inhomogeneous exchange interaction is considered. In the case of a wide straight line of the interface between magnetic media with different but slightly different exchange interaction, the dependence of the magnetic vortex velocity on its distance to the structure defect and position inside the interface domain is obtained.

The time-resolved magneto-optical (MO) Voigt effect can be utilized to study the Néel order dynamics in antiferromagnetic (AFM) materials, but it has been limited for collinear AFM spin configuration. Here, we have demonstrated that in Mn3Sn with an inverse triangular spin structure, the quench of AFM order by ultrafast laser pulses can result in a large Voigt effect modulation. The modulated Voigt angle is significantly larger than the polarization rotation due to the crystal-structure related linear dichroism effect and the modulated MO Kerr angle arising from the ferroic ordering of cluster magnetic octupole. The AFM order quench time shows negligible change with increasing temperature approaching the Néel temperature (TN), in markedly contrast with the pronounced slowing-down demagnetization typically observed in conventional magnetic materials. This atypical behavior can be explained by the influence of weakened Dzyaloshinskii–Moriya interaction rather than the smaller exchange splitting on the diminished AFM order near TN. The temperature-insensitive ultrafast spin manipulation can pave the way for high-speed spintronic devices either working at a wide range of temperature or demanding spin switching near TN., Mn3Sn is an anti-ferromagnetic material which displays a large magneto-optical Kerr effect, despite lacking a ferromagnetic moment. Here, the authors show that likewise, Mn3Sn, also presents a particularly large magneto-optical Voigt signal, with a negligible change in the quench time over a wide temperature range.

Intrinsic magnetic topological insulators offer low disorder and large magnetic bandgaps for robust magnetic topological phases operating at higher temperatures. By controlling the layer thickness, emergent phenomena such as the Quantum Anomalous Hall (QAH) effect and axion insulator phases have been realised. These observations occur at temperatures significantly lower than the Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap at the Dirac point in ultra-thin MnBi2Te4 has yet to be achieved. Critical to achieving the promise of this system is a direct measurement of the layer-dependent energy gap and verifying whether the gap is magnetic in the QAH phase. Here we utilise temperature dependent angle-resolved photoemission spectroscopy to study epitaxial ultra-thin MnBi2Te4. We directly observe a layer dependent crossover from a 2D ferromagnetic insulator with a bandgap greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a large energy gap (>100 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is confirmed to be magnetic in origin, as it abruptly diminishes with increasing temperature above 8 K. The direct observation of a large magnetic energy gap in the QAH phase of few-SL MnBi2Te4 is promising for further increasing the operating temperature of QAH materials.

Magnetic semiconductors with high Curie temper (TC) and inherent ferromagnetism, which not only provide a data-processing function via semiconductors' properties, but also offer a data-storage function through intrinsic ferromagnetism, have become key materials in the field of spintronics. We studied the electronic structures and magnetic properties of Mn-doped cubic (3C) SiC using first-principles calculation. The calculated results revealed that MnSi and MnC substitutions can introduce 3 $$\mu _{{\text{B}}}$$ and 1 $$\mu _{{\text{B}}}$$ magnetic moments into SiC, respectively, which are both localized and extended. The extended tails of the moments indicate a significant spatial extension of the spin-polarized electron states. The interaction between the long tails, which can mediate long-range ferromagnetic (FM) coupling up to 8.55 A, and is very different from common exchange, in which the ferromagnetism decreases sharply with increasing distance between the moments, and is hard to maintain to the next-neighbor order due to the limited spatial spin-electrons distribution. The distributions of magnetic moments become more and more localized or extended as compressive or tensile strains are increased, but FM interactions under compressive and tensile strains are weaker than those in undeformed structure. The FM coupling mechanism is explained and discussed in detail using p–d electron exchange. These results can provide a routine for engineering FM semiconductor of 3C-SiC.

This review presents the results about spin caloritronics obtained at the Department of Low Temperature Physics of the Kharkiv National University from 2017 to 2019 years. Several new directions in magneto-electronics: spintronics, spin caloritronics and magnonics, which emerged with the aim to reduce the energy dissipation in devices of usual semiconductor microelectronics, are discussed. Spintronic devices hold the promise of faster switching speeds, less total energy consumption, and higher density of circuit elements, lowering the heat production per switching element. Then the main results of the four papers published in Physical Review B are discussed: nonlinear relaxation between magnons and phonons in insulating ferromagnets; role of magnons and the size effect in heat transport through an insulating ferromagnet-insulator interface; spin Seebeck effect and phonon energy transfer in heterostructures containing layers of normal metal and ferroinsulator; temperature dependence of the magnon-phonon energy relaxation time in a ferromagnet insulator.

The structure, surface topography and magnetic properties of LaCoO3 (LCO) thin films deposited epitaxially on the SrTiO3 substrates have been investigated in detail. The LCO thin films show a typical ferromagnetic-paramagnetic (FM-PM) phase transition at 78 K. Based on the measurements of isothermal magnetization around the Curie point, the magnetic entropy change (ΔSM) of LCO thin films under various applied magnetic fields were obtained. By utilizing scaling theory, all of the ΔSM curves can be re-scaled, confirming that the FM-PM phase transition is second-order magnetic phase transition. Moreover, the magnetic entropy change -ΔSM features a maximum around TC, whereas, power law fitting of - Δ S M max with H gives n = 0.9704, which is obviously deviating from the standard value n = 2/3 for the Landau mean field model. This indicates that the mean field theory cannot be used to explain the critical behavior of LCO thin films which implies that the critical behavior of LCO thin films may involve complex magnetic interactions. These interactions are correlated with a long-term puzzling finding in this system why its Curie point is always around 80 K regardless of the different fabrication methods and conditions used in the film growth.

The matrix method of Tsai for the calculation of the nonlocal exchange potential has been extended to calculate the plain-wave expanded interstitial part using the Thomas-Fermi damping wave vector. We found enhancement of the 3 d -band exchange splitting and consequently the magnetizations and magnetic moments relative to those obtained by LSDA. By resolving the valence electrons of the Fe, Co, and Ni atoms into spin-polarized s, p, and d components, we found depletion of the itinerant 4 s p electrons that enhances the minority-spin localized d electrons, which is the main cause of the substantial reduction of the magnetic moments in the metals from those of free atoms. Using idealistic domain-wall-free structural models, the magnetizations of these three metals calculated by the exchange-matrix method are overestimated. The overestimates correlate with the exchange energies, which may play a determinative role in the sizes of domain walls.

The quaternary Heusler LuCoTiSi, LuCoTiGe, and LuCoTiSn compounds' physical properties have been investigated using the GGA approximation based on the density functional theory. These compounds are stable in the ferromagnetic phase and semi-stable in the non-magnetic phase. Elastic studies show that these compounds are quite stable and belong to the category of ductile materials. Phonon calculations also show that these two combinations are quite stable, and the phonon levels in the band structure are all in the positive region. The LuCoTiSi, LuCoTiGe, and LuCoTiSn compounds are half-metallic with 100% spin polarization with 2.0µB 3.0 µB, and 2.0µB, respectively. The maximum value of their Seebeck (S) coefficient occurred at 130 K. The figure of merit (ZT) coefficient of these compounds at 100 K equals one and decreased to room temperature with a gentle slope, indicating their thermoelectric efficiency at low and room temperatures. All compounds have accessible regions that referred to their thermodynamic stability. The LuCoTiGe case has a more extensive accessible region than other cases of the thermodynamic phase diagram.

The rotating magnetocaloric effect has been researched in double perovskite Tb $$_{2}$$ CoMnO $$_{6}$$ by Monte Carlo simulation. The magnetization, specific heat and isothermal entropy change are presented for magnetic fields in different directions ( $$h\parallel c$$ and $$h\perp c$$ ). The rotating magnetic entropy, transition temperature and relative cooling power are given as well. Due to the different magnetic anisotropy, the spin of Co $$^{2+}$$ /Mn $$^{4+}$$ is parallel to c axis and the spin of Tb $$^{3+}$$ is perpendicular to c axis. The corresponding A-type antiferromagnetic order appears at $$T_{C} = 94$$ K, and at $$T_{N} = 15$$ K, ferromagnetic state appears. Different orientations of spins result in a big negative and positive rotating magnetic entropy appeared in different temperature. Those findings may provide a wider temperature range for magnetic refrigeration applications.

The effect of interface inhomogeneity on the exchange bias field value in the ferromagnet/antiferromagnet bilayer system is investigated by computer simulation. The case of a thin ferromagnetic film on a thick antiferromagnetic substrate is studied. The Ising model and Metropolis algorithm are used for research. The inhomogeneity of the substrate surface is modeled as random point nonmagnetic impurities. The exchange bias field is determined by the hysteresis loop offset. The dependence of the exchange bias field on the concentration of impurities on the substrate surface at different temperatures is calculated.

We treat elementary excitations, the spin-liquid state, and the anomalous Hall effect (including the quantum one in purely 2D situation) in layered highly correlated systems. The mechanisms of the formation of a topological state associated with bare flat energy bands, correlations, and spin-orbit interactions, including the appearance of correlated Chern bands, are analyzed. A two-band picture of the spectrum in metallic kagome lattices is proposed, which involves a transition from the ferromagnetic state, a flat strongly correlated band, and a band of light Dirac electrons. In this case, the effect of separation of the spin and charge degrees of freedom turns out to be significant. The application of the representations of the Kotliar-Rukenstein auxiliary bosons and the Ribeiro-Wen dopons to this problem is discussed., Review paper, 8 pages

YBa2Cu3O7-δ (or YBCO) superconductors added with various concentrations of dysprosium oxide nanoparticles (NP-Dy2O3) were prepared using the solid-state process. The additive NP-Dy2O3 has a size of about 10 nm and presents a para/ferromagnetic transition at about 300 K. The characterization of samples was probed via XRD, TEM, SEM, DC magnetization, and AC susceptibility measurements. Some models were employed to compute superconducting parameters like intragranular critical current density under a magnetic field (Jcm(H)), the density of intragranular pinning force for Abrikosov vortex (eg(0)), intergranular critical current density (Jc,inter), intergranular electrical character, superconductor grain volume fraction (fs). The correlation between these parameters and microstructure was discussed. The inclusion of NP-Dy2O3 does not alter the structural properties and the spatial growth of YBa2Cu3O7-δ. NP-Dy2O3 addition led to significant enhancements of Jcm(H) and eg(0). The decrement in Jc,inter was attributed to the change of grain boundary characteristics that transformed from SNS to SINS junction due to NP-Dy2O3 addition.

We report on the electronic structure and magnetic properties of hybrid heterostructures combined the ferromagnetic double perovskite Sr2CrOsO6 (SCOsO) and ferroelectric BaTiO3 (BTO) calculated in the GGA approach using the fully relativistic spin-polarized Dirac LMTO method. The electronic band structure is studied in the BTO and SCOsO oxides as well as in SCOsO/BTO hetero structures with different supercells: (1 × 1 × 1) monolayered, (2 × 2 × 1), and (1 × 1 × 2) SCOsO/BTO heterostructures. The optical and magneto-optical spectra of pure BTO and SCOsO oxides as well as of the SCOsO/BTO heterostructures are investigated theoretically and compared with avaliable experimental data. The element-specific x-ray absorption spectra as well as the x-ray magnetic circular dichroism at the Ti, Ba, and Os L2,3 edges in SCOsO/BTO heterostructures are investigated theoretically. Good agreement with experimental spectra has been found.

Ferromagnetic liquids undergo reversible magnetization changes upon varying external magnetic field levels. The movement of ferromagnetic liquid droplets across a coil under an external magnetic field holds promise as an energy transducer from mechanical force to electricity; however, it suffers from an adhesive issue between the ferromagnetic liquid and the solid pedestal. We introduce a superhydrophobic support that uses antiwetting surfaces to remarkably reduce adhesion during the movement of ferromagnetic liquid droplets. Maxwell numerical simulation was utilized to analyze the working mechanism and improve further electrical outputs. By controlling the droplet size, the strength of the magnetic bottom and the tilting speed of the test condition, we generated a ferromagnetic liquid droplet-based superhydrophobic magnetoelectric energy transducer (FLD-SMET) that can convert vibrational energy to electricity. When a 100 μL ferromagnetic liquid droplet was used for FLD-SMET under a 13 mT magnetic field, an electrical voltage response of 280 μV and electrical current response of ∼7.5 μA were generated using a shaking machine with a tilting speed of 9.5°/s. We thus show that such a device can serve as a self-powered light buoy floating on a water surface. Our study presents an applied concept for the design of droplet-based energy harvesters to convert surrounding vibrational energy to electricity.

We consider the nanoscale electronic phase separation in a wide class of different materials, mostly in strongly correlated electron systems. The phase separation turns out to be quite ubiquitous manifesting itself in different situations, where the itineracy of charge carriers competes with their tendency toward localization. The latter is often related to some specific type of magnetic ordering, e.g. antiferromagnetic in manganites and low-spin states in cobaltites. The interplay between the localization-induced lowering of potential energy and metallicity (which provides the gain in the kinetic energy) favors an inhomogeneous ground state such as nanoscale ferromagnetic droplets in an antiferromagnetic insulating background. The present review article deals with the advances in the subject of electronic phase separation and formation of different types of nanoscale ferromagnetic (FM) metallic droplets (FM polarons or ferrons) in antiferromagnetically ordered (AFM), charge-ordered (CO), or orbitally-ordered (OO) insulating matrices, as well as the colossal magnetoresistance (CMR) effect and tunneling electron transport in the nonmetallic phase-separated state of complex magnetic oxides. It also touches upon the compounds with spin-state transitions, inhomogeneous phase-separated state in strongly correlated multiband systems, and electron polaron effect. A special, attention is paid to the systems with the imperfect Fermi surface nesting such as chromium alloys, iron-based pnictides, and AA stacked graphene bilayers., 135 pages, 72 figures, submitted to Physics Reports

The analytical model is constructed for the description of the spin wave propagation through a system consisting of two ferromagnets without and with the Dzyaloshinskii–Moriya interaction, separated by a flat interface. The dependences of transmission and reflection coefficients of spin wave are found as a function of Dzyaloshinskii-Moria constant which is known to be strongly temperature dependent, tending to a significant increase at low temperature.

Electrical transport properties of random binary networks composed of high-Tc superconductor Bi2Sr2Ca2Cu3O10+x (Bi2223) microparticles and half-metal ferromagnet La2/3Sr1/3MnO3 (LSMO) nanoparticles have been investigated. The experimental current-voltage characteristics of bulk samples of nanocomposites with a volumetric content of 4:1 components are well described by the Berezinsky–Kosterlitz–Thouless (BKT) model for two-dimensional (2D) superconductors undergoing a superconducting transition. The observed 2D-like behavior of the three-dimensional transport properties of the nanocomposite is most likely associated with two different physical spatial scales involved in the formation of the properties of the nanocomposite: a significant difference between the geometric dimensions of the constituent components and the appearance of a triplet superconducting state induced by the proximity effect in semi-metallic manganite LSMO contacting Bi2223. Below the Bi2223 superconducting transition temperature, bulk resistive losses in the nanostructures are determined by the current flowing through ferromagnetic LSMO nanoparticles that cover Bi2223 microgranules. As temperature decreases, proximity-induced superconducting transition in the effectively 2D surface of LSMO nanoparticles covering Bi2223 microgranules reveals itself as the topological BKT-like superconducting transition in the bulk sample.

We perform a first-principles calculation to understand the effect of the additional valence electron of the transition atom in Wyckoff position 4 a, on the electronic structure, magnetic and structural stability of the full Heusler $${\mathrm{Mn}}_{2}\mathrm{PtZ}(\mathrm{Z}=\mathrm{V and Co})$$ compound. L21, Xa and tetragonal structures are considered to verify the most stable phase. Within the framework of the plan $${\mathrm{Mn}}_{2}\mathrm{PtZ}(\mathrm{Z}=\mathrm{V and Co})$$ favored the ferromagnetic configuration in the L21 structure. The results show that the 63% and 91% spin polarization at the Fermi level for $${\mathrm{Mn}}_{2}\mathrm{PtV}$$ and $${\mathrm{Mn}}_{2}\mathrm{PtCo}$$ , respectively. The most contribution of the magnetic moment is due to the Mn atom, the total magnetic moments equal to $${4.87\upmu }_{\mathrm{B}}$$ and $${9.012\upmu }_{\mathrm{B}}$$ have been reported. To prove the half metallicity of our compound, we used the GGA + U approach. Within the framework of this approach, the value gap in the minority spin band is 0.755 eV, more, the magnetic moment satisfying the Slater-Pauling rule for the $${\mathrm{Mn}}_{2}\mathrm{PtV}$$ compound. In addition, we give the two values of the curie temperatures for the two cubic structural phases. Finally, both full Heusler $${\mathrm{Mn}}_{2}\mathrm{PtV}$$ and $${\mathrm{Mn}}_{2}\mathrm{PtCo}$$ are a promising candidate for the use of future devices as spin-FETs and nonvolatile magnetic memory.

While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe2, a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature (TC) up to 300 K, an atomic magnetic moment of ~0.21 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mu }_{{\rm{B}}}$$\end{document}μB/Cr and perpendicular magnetic anisotropy (PMA) constant (Ku) of 4.89 × 105 erg/cm3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer (TC ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices., The emergence of two dimensional ferromagnetism suffers from an inherent fragility to thermal fluctuations, which typically restricts the Curie temperature to below room temperature. Here, Zhang et al present CrTe2 thin films grown via molecular beam epitaxy with a Curie temperature exceeding 300 K.

Perpendicularly magnetized synthetic antiferromagnets (SAF), possessing low net magnetization and high thermal stability as well as easy reading and writing characteristics, have been intensively explored to replace the ferromagnetic free layers of magnetic tunnel junctions as the kernel of spintronic devices. So far, utilizing spin-orbit torque (SOT) to realize deterministic switching of perpendicular SAF have been reported while a large external magnetic field is typically needed to break the symmetry, making it impractical for applications. Here, combining theoretic analysis and experimental results, we report that the effective modulation of Dzyaloshinskii-Moriya interaction by the interfacial crystallinity between ferromagnets and adjacent heavy metals plays an important role in domain wall configurations. By adjusting the domain wall configuration between Bloch type and Néel type, we successfully demonstrate the field-free SOT-induced magnetization switching in [Co/Pd]/Ru/[Co/Pd] SAF devices constructed with a simple wedged structure. Our work provides a practical route for utilization of perpendicularly SAF in SOT devices and paves the way for magnetic memory devices with high density, low stray field, and low power consumption., Synthetic antiferromagnets (SAF), formed out of alternating layers of a ferromagnet with neutral spacer combine technologically appealing properties of both antiferromagnets and ferromagnets. Here, Chen et al demonstrate controlled switching of an SAF, without the need for an applied magnetic field.

The magnetic structures of the ground state, phase transitions, and the thermodynamic properties of a two-dimensional ferromagnetic Potts model with the number of spin states q = 4 on a kagome lattice are studied using the Wang-Landau algorithm of the Monte Carlo method, taking into account the interactions of the nearest and the next-nearest neighbors. The studies were carried out for the value of the interaction of the next-nearest neighbors in the range 0 ≤ r ≤ 1.0. It is shown that taking into account the antiferromagnetic interactions of the next-nearest neighbor leads to a violation of the magnetic ordering. A phase diagram of the dependence of the critical temperature on the value of the interaction of the next-nearest neighbor is constructed. The analysis of the character of phase transitions is carried out. It was found that in the ranges 0 ≤ r ≤ 0.5 and 0.5 ≤ r ≤ 1.0, a first-order phase transition is observed, and for r = 0.5, frustrations are observed in the system.

Based on the full-potential linearized augmented plane wave (FP-LAPW) method, we have investigated the electronic, structural, magnetic and optical properties of Cd0.9375TM0.0625S (TM = Mn, Fe, Co and Ni) compounds in the zinc-blende (ZB) ferromagnetic phase. The magnetic and electronic properties are treated using the PBE-GGA and TB-mBJ approximations. CdS is well known as a non-magnetic semiconductor. When CdS is doped with a transition metal (TM), Cd0.9375TM0.0625S (TM = Mn, Fe, Co) changes to half-semiconductors (HSC) and Cd0.9375Ni0.0625S to a half-metal (HM). It is found that the 3d-t2g states of the transition metal are responsible for generating spin polarization and magnetic moment in these compounds. All the considered compounds are ferromagnetic and the calculated total magnetic moment increases from 2 to 5 µB moving from Ni to Mn. The optical properties exhibited new peaks in the visible and ultraviolet regions due to the effect of free-carrier absorption related to the magnetic impurities. Our results show very good agreement to previous theoretical and experimental data. The results presented herein imply that TM-doped CdS has potential for applications in spintronic and optoelectronic device sectors in a wide energy range of the light spectrum from visible to ultraviolet.

van der Waals crystals exhibit excellent material performance when exfoliated to few-atomic-layer thickness. In contrast, the van der Waals thin films more than 10 nm thick are believed to show bulk properties, in which outstanding material performance is rarely found. Here we report the largest anomalous Hall conductivity observed so far in a 170 nm van der Waals ferromagnetic 1T-CrTe2 flake, which reaches 67,000 Ω-1 cm-1. Such a colossal anomalous Hall conductivity in 1T-CrTe2 is dominated by the extrinsic skew scattering process rather than the intrinsic Berry phase effect, as evidenced by the linear relation between the anomalous Hall conductivity and the longitudinal conductivity. Defying the dilemma of mutually exclusive large anomalous Hall angle and high electric conductivity for most ferromagnets, 1T-CrTe2 achieves both in a thin film sample. Considering the shared physics of the anomalous Hall effect and the spin Hall effect, our finding offers a guideline for searching large spin Hall materials of high conductivity which may overcome the bottleneck of overheating in spintronics devices.

The magnetic phases of cubic chiral ferromagnets with the Dzyaloshinskii–Moriya interaction (MnSi, Cu2OSeO3) are studied in terms of microscopic and phenomenological approaches. The interaction of the magnetic moments of atoms with a local crystal field is shown to cause a cubic anisotropic term $$M_{x}^{4}$$ + $$M_{y}^{4}$$ + $$M_{z}^{4}$$ (M is the magnetization field) in the Landau–Lifshitz energy. This term is responsible for the existence of the helical phase at a near-zero magnetic field and can contribute to the stability of the magnetic A phase in higher fields. The A phase is simulated at various magnetic fields. When a magnetic field is turned on, the helices in the helical phase are shown to acquire elliptical and conical components.