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Polar Rashba-type semiconductor BiTeI doped with magnetic elements constitutes one of the most promising platforms for the future development of spintronics and quantum computing thanks to the combination of strong spin-orbit coupling and internal ferromagnetic ordering. The latter originates from magnetic impurities and is able to open an energy gap at the Kramers point (KP gap) of the Rashba bands. In the current work using angle-resolved photoemission spectroscopy (ARPES) we show that the KP gap depends non-monotonically on the doping level in case of V-doped BiTeI. We observe that the gap increases with V concentration until it reaches 3% and then starts to mitigate. Moreover, we find that the saturation magnetisation of samples under applied magnetic field studied by superconducting quantum interference device (SQUID) magnetometer has a similar behaviour with the doping level. Theoretical analysis shows that the non-monotonic behavior can be explained by the increase of antiferromagnetic coupled atoms of magnetic impurity above a certain doping level. This leads to the reduction of the total magnetic moment in the domains and thus to the mitigation of the KP gap as observed in the experiment. These findings provide further insight in the creation of internal magnetic ordering and consequent KP gap opening in magnetically-doped Rashba-type semiconductors.

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We consider a system of nonlinear differential equations describing the antiferromagnetism victor in a ferrite film. The system contains two parameters and admits a family of exact solutions with plane phase trajectories. Perturbation of such solutions leads to the Hill equation with periodic coefficient. We study the stability of the equilibrium state of the Hill equation.

The piezoelectric effect theory is developed in rare-earth ferroborates. It is established that mainly single-ion mechanisms are responsible for the appearance of the effect: the existence of mechanical stresses leads to the induction in a crystal of dipole electric moments immediately in electron 4f shells of rare-earth ions, which leads to the crystal polarization. The effect is considered quantitatively for neodymium and samarium ferroborates; in particular, in the range from 0 K to 300 K, the temperature dependences of piezoelectric moduli have been obtained. In addition, it is shown that, at temperatures lower than the Neel point, the deformation of a crystal in magnetic field can lead to the appearance of the crystal polarization along crystallographic axis c. The temperature, field, and orientation dependences of the magnetically induced piezoelectric moduli are calculated.

In this work, we perform a comparative study of the magnetization behavior of four series of compounds R2Fe14B and their hydrides R2Fe14BH5.5, and the compositions (Nd0.5R0.5)2Fe14B and their hydrides (Nd0.5R´0.5)2Fe14BH5.5 with R and R´ = Ho, Er, and Tm. The magnetization is measured in pulsed magnetic fields up to 58 T and in megagauss fields up to 135 T at 5 K. The first and second critical fields of the field-induced transitions, Hc1 and Hc2 were estimated analytically and the results were verified against experimental data. We find that hydrogenation of R2Fe14B and (Nd0.5R´0.5)2Fe14B reduces drastically the Hc1 and Hc2 values and, as a consequence, the intersublattice R–Fe exchange interaction parameter λ.

We propose a novel type of photonic-crystal (PC)-based nanostructures for efficient and tunable optically-induced spin current generation via the spin Seebeck and inverse spin Hall effects. It has been experimentally demonstrated that optical surface modes localized at the PC surface covered by ferromagnetic layer and materials with giant spin-orbit coupling (SOC) notably increase the efficiency of the optically-induced spin current generation, and provides its tunability by modifying the light wavelength or angle of incidence. Up to 100% of the incident light power can be transferred to heat within the SOC layer and, therefore, to the spin current. Importantly, the high efficiency becomes accessible even for ultra-thin SOC layers. Moreover, the surface patterning of the PC-based spintronic nanostructure allows for the local generation of spin currents at the pattern scales rather than the diameter of the laser beam.

We perform a high-field magnetization study for the single-crystalline ferrimagnetic ErFe11Ti compound in order to redefine the crystal-field and exchange parameters. For the first time, we predict theoretically the magnetization behavior of ErFe11Ti up to 100 T magnetic field. The latter allows us to observe the full magnetization process (up to the forced-ferromagnetic state) in ErFe11Ti. The results are compared with data for the hydride ErFe11TiH1.

Phase transitions in multiferroics with spatially modulated structures as ground states are studied in this work. The key physical mechanisms needed to implement modulated states of various kinds (cycloidal and helicoidal magnetic phases) and the conditions of phase transitions within modulated states are discussed. The domain of physical parameters where the ground state of the spin cycloid becomes unstable is determined for single crystals and films of bismuth ferrite. It is demonstrated that the domains of existence and stability of spin cycloids differ. Analytical estimates of their boundaries are obtained. The behavior of the spin system in a (110) BiFeO3 film in the magnetic field is studied, and diagrams of the ground magnetic states are plotted.

We consider a system of nonlinear autonomous differential equations that describe the orientation of the antiferromagnetic vector in a multiferroic film and find the conditions for the existence of spatially modulated structures of the cycloid type. We investigate the stability of such structures under spatial perturbations.

We present experimental high-field magnetization studies for the single-crystalline ferrimagnetic RFe11Ti compounds at example of holmium-based hydride in order to evaluate, compare and analyze the crystal-field and exchange parameters. We predict theoretically the magnetization behavior of HoFe11Ti up to 80 T magnetic field for the first time. The results are compared with data for the parent compound HoFe11TiH1 and those with erbium and thulium (x = 0 and 1).

Understanding how fast short-range interactions build up long-range order is one of the most intriguing topics in condensed matter physics. FeRh is a test specimen for studying this problem in magnetism, where the microscopic spin-spin exchange interaction is ultimately responsible for either ferro- or antiferromagnetic macroscopic order. Femtosecond laser excitation can induce ferromagnetism in antiferromagnetic FeRh, but the mechanism and dynamics of this transition are topics of intense debates. Employing double-pump THz emission spectroscopy has enabled us to dramatically increase the temporal detection window of THz emission probes of transient states without sacrificing any loss of resolution or sensitivity. It allows us to study the kinetics of emergent ferromagnetism from the femtosecond up to the nanosecond timescales in FeRh/Pt bilayers. Our results strongly suggest a latency period between the initial pump-excitation and the emission of THz radiation by ferromagnetic nuclei., 35 pages total, 8 figures in main text, 7 figures in supplementary

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Optical pump-probe setups are commonly used for excitation and investigation of the spin dynamics in various types of magnetic materials. Usually spatially homogeneous excitation is considered, but here the authors describe the optical excitation of the $n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}f\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}m$ terahertz spin dynamics that are due to the intrinsic anisotropic properties of a weakly ferromagnetic material. They furthermore present an approach for probing and restoring the spatial distribution inside a magnetic crystal, which allows one to properly interpret the experimental results and obtain the complete picture of nonuniform terahertz spin dynamics.

Recently discovered intrinsic antiferromagnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ Dirac cone. Here, using micro($\ensuremath{\mu}$)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the N\'eel temperature at about 10--16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the $\mathrm{Mn}{\mathrm{Bi}}_{2}{\mathrm{Te}}_{4}$ DP gap size.

Experimental studies of anomalous Hall effect are performed for thin filmed Ta/TbFeCo in a wide range of temperatures and magnetic fields up to 3 T. While far from the compensation temperature (TM=277 K) the field dependence has a conventional shape of a single hysteresis loop, just below the compensation point the dependence is anomalous having the shape of a triple hysteresis. To understand this behavior, we experimentally reveal the magnetic phase diagram and theoretically analyze it in terms of spin-reorientation phase transitions. We show that one should expect anomalous hysteresis loops below the compensation point if in the vicinity of it the magnetic anisotropy is dominated by FeCo sublattice due to interaction with Ta., Comment: 9 pages, 6 figures

The efficiency of the ultrafast excitation of spins in antiferromagnetic $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ using a nearly single-cycle THz pulse is studied as a function of the polarization of the THz pulse and the sample temperature. Above the Morin point the most efficient excitation is achieved when the magnetic field of the THz pulse is perpendicular to the antiferromagnetically coupled spins. Using the experimental results and equations of motion for spins, we show that the mechanism of the spin excitation above and below the Morin point relies on a magnetic-dipole interaction of the THz magnetic field with spins, and the mechanism implies that the efficiency of the coupling is proportional to the time derivative of the magnetic field.

THz magnetization dynamics is excited in ferrimagnetic thulium iron garnet with a picosecond, single-cycle magnetic field pulse and seen as a high-frequency modulation of the magneto-optical Faraday effect. Data analysis combined with numerical modelling and evaluation of the effective Lagrangian allow us to conclude that the dynamics corresponds to the exchange mode excited by Zeeman interaction of the THz field with the antiferromagnetically coupled spins. We argue that THz-pump IR-probe experiments on ferrimagnets offer a unique tool for quantitative studies of dynamics and mechanisms to control antiferromagnetically coupled spins., Comment: 17 pages, 16 figures

In this paper, the full magnetization process demonstrated by the series of ferrimagnetic intermetallic compounds ${(\mathrm{Nd},\mathrm{Ho})}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ and ${\mathrm{Ho}}_{2}{\mathrm{Fe}}_{14}\mathrm{B}$ and their hydrides with the maximum possible hydrogen content (for the given crystal structure type) is studied theoretically and experimentally using megagauss magnetic fields. We observe field-induced phase transitions from the initial ferrimagnetic to the forced-ferromagnetic state in magnetic fields up to 130 T and describe the magnetization process analytically. We find a drastic decrease of the critical transition fields in the hydrogenated compounds. This is due to extremely strong, nearly twofold reduction of the $R$-Fe intersublattice exchange interaction because of the combined substitution and hydrogenation effects. A comparative analysis of the magnetization behavior for the system ${\mathrm{Ho}}_{2}{\mathrm{Fe}}_{17}\text{\ensuremath{-}}\mathrm{H}$ is also performed.

We report on a theoretical study of the spin-current excited dynamics of domain walls (DWs) in ferrimagnets in the vicinity of the angular momentum compensation point. Effective Lagrangian and nonlinear dynamic equations are derived for a two-sublattice ferrimagnet taking into account both spin-torques and external magnetic field. The dynamics of the DW before and after the Walker breakdown is calculated for any direction of the spin current polarization. It is shown that for the in-plane polarization of the spin current, the DW mobility reaches a maximum near the temperature of the angular momentum compensation. For the out-of-plane spin polarization, in contrast, a spin current with the densities below the Walker breakdown does not excite the dynamics of the DW. After overcoming the Walker breakdown, the domain wall velocity increases linearly with increasing the current density. In this spin-current polarization configuration the possibility of a gigahertz oscillation dynamics of the quasi-antiferromagnetic vector under the action of a damping-like torque in the angular momentum compensation point is demonstrated. Possible structures for experimental demonstration of the considered effects are discussed., 7 pages, 6 figures

Understanding how fast short-range interactions build up long-range order is one of the most intriguing topics in condensed matter physics. FeRh is a test specimen for studying this problem in magnetism, where the microscopic spin-spin exchange interaction is ultimately responsible for either ferro- or antiferromagnetic macroscopic order. Femtosecond laser excitation can induce ferromagnetism in antiferromagnetic FeRh, but the mechanism and dynamics of this transition are topics of intense debates. Employing double-pump THz emission spectroscopy has enabled us to dramatically increase the temporal detection window of THz emission probes of transient states without sacrificing any loss of resolution or sensitivity. It allows us to study the kinetics of emergent ferromagnetism from the femtosecond up to the nanosecond timescales in FeRh/Pt bilayers. Our results strongly suggest a latency period between the initial pump-excitation and the emission of THz radiation by ferromagnetic nuclei.

In this paper, we elaborate analytical theory of domain wall dynamics close to the angular momentum compensation point based on non-linear dynamic equations derived from the effective Lagrangian of a ferrimagnet. Analysis of the precession angle and domain wall velocity oscillations in post Walker regime in a ferrimagnet is performed. In the framework of the proposed model, we explore dynamic processes in the Walker and post Walker regimes. We show that although spin oscillations quench the dynamics of domain walls near the Walker breakdown field, a further increase of the driving magnetic field increases domain wall speed and mobility. An anomalous behavior of domain wall dynamic properties near the angular momentum compensation point in ferrimagnets is discussed., 16 pages, 4 figures

Currently, active research is aimed at perovskite-based oxides, including rare earth orthochromites, which exhibit magnetoelectric properties owed to intrinsic magnetic interactions in external electric and magnetic fields. Due to a variety of structural instabilities and couplings in these materials, understanding the underlying magnetoelectric mechanisms is a challenge. In this paper, we explore magnetoelectric properties of the rare earth orthochromites in the framework of symmetry analysis. Our calculations show the presence in

A numerical and analytical study of the dynamics of domain walls (DWs) in a magnetic tunnel junction with perpendicular magnetic anisotropy in a free layer is presented. Equilibrium states of the domain wall are obtained for various widths of the structure. The corresponding symmetries of the components of spin transfer torques ${\mathbf{T}}_{STT}$ and the polarizer directions favoring stable DW motion under perpendicular current injection are obtained. The DW steady motion with velocities up to 200 m/s at current densities below ${10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$ is reported. The Walker breakdown is demonstrated, and the dynamics of the postthreshold DW motion is investigated for various configurations of torques and polarizer directions. To have analytical insight into the investigated regimes of DW dynamics a theoretical model is developed and verified by micromagnetic simulations.

Coupling up of spins and lattice The development of spintronics and magnetic data storage relies on understanding and controlling the dynamics of magnetic excitations within a material. Of crucial importance for practical applications is how fast the magnetization can be switched. Mashkovich et al . report the use of ultrafast terahertz radiation to create magnon excitations in the antiferromagnet cobalt difluoride that can then be coupled with phonon excitations (see the Perspective by Juraschek and Narang). Using light to control coupling between the spins and the lattice provides a route to manipulate magnetization in antiferromagnetic materials on ultrafast time scales. —ISO

Spin waves in magnetic microresonators are at the core of modern magnonics. Here we demonstrate a new method of tunable excitation of different spin wave modes in magnetic microdisks by using a train of laser pulses coming at a repetition rate higher than the decay rate of spin precession. The microdisks are etched in a transparent bismuth iron garnet film and the light pulses influence the spins nonthermally through the inverse Faraday effect. The high repetition rate of the laser stimulus of 10 GHz establishes an interplay between the spin wave resonances in the frequency and momentum domains. As a result, the excitation efficiency of different spin modes can be tuned by a small variation of the external magnetic field. An additional degree of freedom is provided by scanning the laser spot within the microdisk area. This makes the proposed method for spin wave excitation advantageous for the forthcoming application of magnonics for telecommunication and quantum technologies.

The transverse magneto-optical effect in transmission is addressed in plasmonic nanostructures with three different kinds of spatial symmetry breaking. The features of the transverse magnetophotonic effect in transmission in each of the asymmetric magnetoplasmonic nanostructures are reported.

As magnetized media by their nature have broken time reciprocity, the spatial symmetry of a material is also crucial and it imposes some restrictions on observed optical phenomena. Thus, for the normal incidence of light the spatial inversion symmetry makes transmitted and reflected light insensitive to the direction of the in-plane magnetization of the sample. To avoid this limitation, we propose here an approach based on a magnetoplasmonic structure with broken spatial symmetry. Combination of the specially designed spatial asymmetry with magnetism in the presence of optical losses provides a different effect, the transverse magnetophotonic transmittance effect, notable magnetooptical modulation of the optical transmittance at normal incidence enhanced by surface plasmon excitation. As the phenomenon is sensitive to asymmetry, it can serve as a powerful tool to study spin waves and currents in magnonic and optospintronic devices. The approach to marry the concepts of magnetoplasmonics and a lack of spatial symmetry is promising for the design of nanophotonics devices with outstanding properties.

Herein, the filling of single‐walled carbon nanotubes (SWCNTs) with sulfur is performed, and the magnetic properties of the formed nanomaterials are studied. Encapsulation of sulfur species results in the appearance of a specific magnetic ordering in the system due to the formation of nanoscopic grains composed of sulfur and residual catalytic Fe nanoparticles contained in the SWCNTs. The magnetic character of the obtained 1D nanostructures is studied using superconducting quantum interference device (SQUID) magnetometer and a sequential ferromagnetic–antiferromagnetic ordering in the material is revealed. Magnetic and optical properties are strongly dependent on the synthesis protocols. A significant Raman intensity increase related to the encapsulated nanostructures is obtained when filling is performed at high‐pressure high‐temperature conditions. Simultaneously, the magnetic susceptibility gets strongly reduced for high‐pressure filling, which is related to the escape of iron particles from the nanotube interior, and the magnetic properties of the material are governed by a weak ferromagnetic ordering of Fe–S structures remained inside SWCNTs. Sulfur encapsulation provides the new route for controlling the magnetic properties in 1D nanomaterials that pave the way for advanced magneto‐optical applications. Post-print / Final draft

Alterations in the ground state of thin (001) films of a BiFeO3 (BFO)-type multiferroic in a magnetic field are studied theoretically, with changes in the energy of induced anisotropy taken into account. The anisotropy vs. field phase diagrams identifying the stability regions of homogeneous antiferromagnetic states and the regions of emergence of spatially modulated antiferromagnetic states are constructed for three mutually orthogonal orientations of applied magnetic field. We show that, as the magnetic field decreases, the transformation of a homogeneous phase into a spatially modulated state occurs at the instability point of the homogeneous state via gradual emergence of the conical phase that transforms into a planar cycloid with the decreasing magnetic field. A multiferroic film grown on a (001) substrate develops considerable anisotropy of the energy of spatially modulated state, depending on the modulation orientation. Meanwhile, cycloids with different orientations undergo the transitions from incommensurate phase into the homogeneous state differently: either the conical cycloid is formed followed by its collapse into the homogeneous state or an unlimitedly growing domain of the homogeneous phase is formed within the flat cycloid. Examples of field-induced changes in magnetization, with changes in spin states taken into account, are provided. These results are of value in practical applications of multiferroic strain engineering.

We report on the novel cycloids that can be realized in epitaxial BiFeO3 films. We found two featured (1 1 0) and ( 1 1 ¯ 0 ) plane cycloids in the (1 1 0) oriented BiFeO3 film and considered the action of compressive and tensile deformations on the areas of the cycloids stability. Our findings show that additional magnetic anisotropy induced by the strains allocates cycloids with the definite directions of spin rotation and electric polarization and change the properties of space modulated structures. Until now, it was believed that polarization is linked with antiferromagnetic order throughout the plane of spin rotation, namely it was considered that polarization always lies in the cycloid spin rotation plane. We show that due to the action of epitaxial strains spin rotational plane of the cycloid deviates from the plane containing intrinsic spontaneous polarization Ps.

We present a theoretical study of the spin dynamics in perovskite-like multiferroics with homogeneous magnetic order in the presence of external magnetic and electric fields. A particular example of such material is BeFeO3 in which the spin cycloid can be suppressed by application of external magnetic field, doping or by epitaxial strain. Understanding the effect of the external electric field on the spin-wave spectrum of these systems is required for devices based on spin wave interference and other innovative advances of magnonics and spintronics. Thus, we propose a model for BiFeO3 in which the thermodynamic potential is expressed in terms of polarization \boldsymbol{P}, antiferrodistortion \boldsymbol{\Omega}, antiferromagnetic moment \boldsymbol{L} and magnetization \boldsymbol{M}. Based on this model, we derive the corresponding equations of motion and demonstrate the existence of electromagnons, that is, magnons that can be excited by electric fields. These excitations are closely related to the magnetoelectric effect and the dynamics of the antiferrodistortion \boldsymbol{\Omega}. Specifically, the influence of the external electric field on the magnon spectra is due to reorientation of both polarization \boldsymbol{P} and antiferrodistortion \boldsymbol{\Omega} under the influence of the electric field and is linked to emergence of a field-induced anisotropy.

The substitution of rare-earth ions has been recognized as an effective way to modify the multiferroic properties, especially to realize the electric field-controlled magnetism in BiFeO3 ceramics, in which the symmetry modulation of R3 c/ Pna21 and the unlocked ferromagnetism through breaking the cycloidal spin structure are the key issues. Here, the enhancement of ferroelectric polarization and weak ferromagnetism are investigated in Bi1− xLa xFeO3 ceramics together with the magnetoelectric coupling coefficient αME with the development of the Pna21 phase. The expected electric field-controlled magnetism is achieved at the phase boundary through the electric field-induced transition of Pna21/ R3 c, where the variation of magnetization reaches 34.18 emu/mol (58.95%) at x = 0.18 after poling.

The features of ultrafast spin dynamics excitation using high-intensity femtosecond laser pulses in magnetic materials are reviewed. Key mechanisms of a pump pulse action on the spin system of a magnetic material are discussed, including the inverse Faraday effect in yttrium-iron garnet; induced magnetic anisotropy in the thulium orthoferrite, and the thermal driving of a magnetic system out of equilibrium in the case of the metallic ferrimagnet GdFeCo, which is a promising material for magnetic memory and terahertz spintronics. It was shown that, apart from using conventional magneto-optical methods for probing the magnetization dynamics in magnetic heterostructures, the inverse spin Hall effect can also be used, an approach that potentially enables the development of memory elements in which the ultrafast optical control of magnetization is combined with electrical detection.