An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X23550021

The injection of a pure spin current into a conducting helimagnet is investigated. The characteristic decay lengths for the spin current injected into the helimagnet are determined, and their physical meaning is described. It is shown that instead of the spin diffusion length, helimagnets are characterized by the decay length that is always smaller than the spin diffusion length, the difference in these lengths being determined by the ratio of the helimagnet spiral period to the spin diffusion length. We predict the existence of the “effect of the chiral polarization of a pure spin current,” i.e., the emergence of the spin current with longitudinal (transverse) polarization, which depends on the spiral chirality, upon the injection of a pure spin current with the transverse (longitudinal) polarization relative to the spiral axis.

Flexible spin valves were prepared by magnetron sputtering on polyimide substrates. The buffer layer that reduces significantly the effect of the polymer substrate on the spin valve microstructure and magnetoresistive properties was revealed. Bending deformation was applied to the microobjects based on the flexible spin valves in parallel to anisotropy axes. It was revealed that during the bend the magnetoresistance changes due to the joint impact of both the change of the magnetic field projection on the film plane and the change of the magnetic properties of the ferromagnetic layers. The obtained dependences have been used in construction of bending sensor, in which the flexible spin valve microstripes were united into the Wheatstone bridge.

A theory of spin and charge transport in bounded metallic magnets has been constructed, which takes into account the effects of spin-orbit scattering of conduction electrons by crystal lattice defects. The theory can be used to describe the spin Hall effect and the anomalous Hall effect and can serve as a basis for describing the phenomena of spin-orbitronics. Phenomenological boundary conditions for the charge and spin fluxes at the interface between two different metals have been formulated, on the basis of which the injection of a pure spin current into a helimagnet, which arises in a normal metal as a manifestation of the spin Hall effect, is described. The existence of an “effect of chiral polarization of a pure spin current” is predicted, which consists in the appearance in a helimagnet of a longitudinally polarized pure spin current and a longitudinal component of the nonequilibrium electron magnetization, depending on the chirality of the helimagnet helix, upon injection of a transversely polarized spin current from a normal metal.

The frequency dependence of the nonequilibrium magnetization arising in an electron gas due to spin injection from a half-metallic ferromagnet into a nonmagnetic material is theoretically analyzed. It is shown that high-frequency spin injection gives rise to nonequilibrium magnetization waves, which decay at a length much smaller than the spin diffusion length. This reduces the efficiency of spin injection.

The Ta/Dy/Ta nanostructures are fabricated by high-vacuum magnetron sputtering. Resistance and longitudinal magnetoresistance are measured. It is shown that the observed the effect of magnetic field on resistance are due to the competition of two effects of different nature. The negative isotropic magnetoresistance in the dysprosium layer is due to the alignment of local magnetic moments in the direction of the applied magnetic field. The positive longitudinal magnetoresistance in tantalum layers is caused by a change in the conditions of scattering of electrons during the accumulation of electrons with opposite spins on opposite surfaces of the metal film with strong spin-orbit coupling.

A quantum theory of electron spin transport in conductive magnets is developed. The theory describes a large number of effects that arise due to spin-orbit scattering of conduction electrons on crystal lattice defects, such as the spin Hall effect, the inverse spin Hall effect, and the anomalous Hall effect. The transport through the contact of two different conductive magnetics is also considered; the phenomenological boundary conditions for the charge and spin flows are formulated, which make it possible to take into account the spin flip at the interface. The developed electron spin transport theory is used to describe the spin-orbitronics of the “helimagnet metal/non-magnetic metal” heterojunction. The spatial distribution of the polarization of the spin current injected into the helimagnet is found, and the characteristic decay lengths of different components of the polarization vector of the spin current are determined.

An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X23550021

Spin valves containing a Dy layer have been formed on an elastic polyimide film by magnetron sputtering. The field dependences of the magnetoresistance of samples subjected to different tensile deformations have been measured. The character of the variations of the magnetoresistive properties of a spin valve subjected to tensile deformation is shown to depend on the thickness of the dysprosium layer. In particular, the thickness of the dysprosium layer affects the maximum relative elongation at which the magnetoresistance of spin valves remains unchanged.

Spin valves containing a Dy layer have been formed on an elastic polyimide film by magnetron sputtering. The field dependences of the magnetoresistance of samples subjected to different tensile deformations have been measured. The character of the variations of the magnetoresistive properties of a spin valvesubjected to tensile deformation is shown to depend on the thickness of the dysprosium layer. In particular, the thickness of the dysprosium layer affects the maximum relative elongation at which the magnetoresistanceof spin valves remains unchanged.

The nonequilibrium magnetization (spin polarization) of conducting electrons moving in materials with a nonuniform magnetization distribution is analyzed theoretically. Both stationary states and transient processes occurring upon the current switching on and off are considered. Because of the coordinate dependence of the magnetization, the passage of current leads to a deviation of the charge carrier magnetization from its equilibrium value. Based on a simple model for nonequilibrium magnetization, the expression describing the coordinate dependence of the nonequilibrium magnetization is obtained in terms of the drift length and the spin diffusion length. It is shown that the effect is the strongest when the coordinate derivative of the magnetization is maximal. Various examples of media with a nonuniform magnetization are considered, including periodic structures such as spin density waves and artificial superlattices.

The absorption spectra of a CoFe 2 O 4 ferrite spinal single crystal, which has a giant magnetostriction, demonstrate an absorption edge at 1.18 eV and a fine structure of impurity absorption bands in the IR region. In the Voight geometry, the crystal is shown to exhibit magnetoabsorption, which is related to the field-induced changes in the fundamental absorption edge and impurity absorption bands. The magnetoabsorption (magnetotransmission and magnetoreflection of light) is anisotropic and depends on the magnetic field direction with respect to the crystallographic axes of the crystal. The light magnetoabsorption is found to be related to the magnetostriction of the crystal. The magnetostriction of CoFe 2 O 4 is shown to significantly contribute to its magnetic anisotropy constant, which is accompanied by changes in the electronic spectrum and optical properties when a magnetic field is applied. The high magnetoabsorption in CoFe 2 O 4 in a relatively low magnetic field makes it possible to use this magnetic material for the development of a new trend in spintronics, namely, strain-magnetooptics.

Spin injection from ferromagnet into nonmagnetic semiconductor is theoretically investigated for the case when the electric current in ferromagnet/semiconductor structure depends on time. The study of switching on/off dc current showed that the time dependence of the magnetization at any point inside semiconductor does not obey the exponential law with spin relaxation time τs.

N. O. Antropov, 2 E. A. Kravtsov, M. V. Makarova, V. V. Proglyado, T. Keller, 4 I. A. Subbotin, E. M. Pashaev, G. V. Prutskov, A. L. Vasiliev, Yu. M. Chesnokov, N. G. Bebenin, V. V. Ustinov, B. Keimer, and Yu. N. Khaydukov 4, 6 Institute of Metal Physics, 620180 Ekaterinburg, Russia Ural Federal University, 620002 Ekaterinburg, Russia Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany Max Planck Society Outstation at the Heinz Maier-Leibnitz Zentrum (MLZ), D-85748 Garching, Germany National Research Center ”Kurchatov Institute”, 123182 Moscow, Russia Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow 119991, Russia (Dated: February 2, 2021)

The infrared optical, magneto-optical properties of CoFe2O4 single crystals are considered. The magneto-absorption of natural light in the infrared spectral range in CoFe2O4 spinel is studied in the Voight experimental geometry. This magneto-optical effect is very high and associates with a change in the fundamental absorption edge and impurity absorption bands under a magnetic field. The magneto-absorption strongly depending on both the magnitude and the orientation of the magnetic field relative to the crystallographic axes of the crystal is presented in this paper. The contribution of magnetostriction to the magnetic anisotropy constant of the CoFe2O4 crystal is shown to be abnormally large. The clear connection between magneto-absorption of light in the infrared spectral range and magnetostriction of the CoFe2O4 spinel is established.

The correlation between magnetoreflection, magnetotransmission of unpolarized light in the infrared range and the magnetoelastic properties of magnetics is reported for the ferrimagnetic spinel CoFe2O4 single crystal. The new physical mechanism responsible for the spectral and field-dependent peculiarities of magnetoreflection and magnetotransmission in the ferrite-spinel possessing strong magnetostriction is discussed. The influence of a magnetic field on specular reflection and transmission spectrum is likely to be indirect: magnetic-field-induced strong strains and deformations of the crystal lattice lead to the change in the electron energy structure and, hence, optical properties of CoFe2O4. The revealed mechanism of new infrared magnetooptical effect in magnetostrictive magnetics paves the way towards new research area called as a strain-magneto-optics.

The peculiarities of spin and charge kinetics in helical magnetic metals that are due to forces acting on the magnetic moment of conduction electrons in inhomogeneous magnetic field have been considered. Analyzing the equations of motion for non-equilibrium spin density shows that an electric field directed along the axis of the helix produces conduction-electron spin polarization along this direction. Under the same conditions, the directions of polarization of the spin current and polarization of the locally equilibrium spin density are collinear. The specific structure of the effective exchange field acting on the conduction electrons in helical magnets causes two additional spin relaxation mechanisms to emerge. In addition to the mechanism of spin-lattice relaxation, “diffusion” and “precession” mechanisms of spin relaxation exist in conductive helical magnets. The diffusion mechanism is analogous to the Dyakonov-Perel spin relaxation mechanism. The key point is that the inhomogeneities of a magnetic field initiate a coupling between the spin and charge systems. It has been shown that, in a helical metal, the electrical conductivity decreases due to the action of the non-uniform exchange magnetic field.

AbstractThe reflection spectra of FeGe_2 single crystal in a wide spectral region and in the temperature range from 80 to 310 K are studied. The energy of plasma oscillations, the relaxation frequency of charge carriers, and phonon frequencies are determined. Anisotropy of the optical properties is studied. It is shown that the phase transition from the collinear antiferromagnetic structure to the spiral one is accompanied by a significant rearrangement of electronic states.

The temperature dependences of the electrical resistivity and magnetization of the Ni50Mn36Sb14–xZ x (Z = Al, Ge; x = 0; 2) alloys have been used to determine the characteristic phase transition temperatures. The isothermal entropy change ΔS was determined using Maxwell’s equation and the field dependences of magnetization. The partial substitution of Ge for Sb has been shown to result in a slight increase in ΔS and a shift in the ΔS maximum to the low-temperature range. The substitution of Al for Sb leads to a decrease in the effect and shift in the ΔS maximum to the high-temperature range. It has been found that the maximum magnetocaloric effect has been observed for the Ni50Mn36Sb12Ge2 composition and is equal to ΔS = 1.3 J/(kg K) in a field change of 10 kOe.