Dzyaloshinsky Moriya Research Articles

Current-induced domain wall motion attributed to spin Hall effect and Dzyaloshinsky–Moriya interaction in Pt/GdFeCo (100 nm) magnetic wire

We investigated the current-induced domain wall motion (CIDWM) in Pt/GdFeCo bilayer wires where the thicknesses of the GdFeCo layer are 110 and 150 nm. We found that the direction of CIDWM in the Pt/GdFeCo wires is the same as the current flow direction. The velocity of the domain wall depends on the in-plane magnetic field. These results indicate that the CIDWM along the current direction in the Pt/GdFeCo wires is probably attributed to the spin Hall effect and Dzyaloshinsky–Moriya interaction. Generally, these effects do not appear in thick magnetic wires because they effectively occur at the interfaces of a heavy metal and magnetic layers. Therefore, these results are interesting phenomena because they probably suggest that the spin Hall effect and Dzyaloshinsky–Moriya interaction in the Pt/GdFeCo wire have an anomalously long-range influence.

Localized spin excitations in an antiferromagnetic spin system with D-M interaction.

The existence of localized spin excitations and spin deviations along the site in a one-dimensional antiferromagnet with Dzyaloshinski-Moriya (D-M) interaction has been studied using quasiclassical approximation. By introducing the Holstein-Primakoff bosonic representation of spin operators, the coherent state ansatz, and the time dependent variational principle, a discrete set of coupled nonlinear partial differential equations governing the dynamics is derived. Employing the multiple-scale method, one, two and three solitary wave solutions are constructed and depicted graphically.

Renormalized entanglement in Heisenberg-Ising spin-1/2 chain with Dzyaloshinskii-Moriya interaction

The influence of the Dzyaloshinsky-Moriya (DM) interaction on entanglement in the one-dimensional spin-1/2 Heisenberg-Ising model is investigated via concurrence. The existence of two states, different in quantum properties and linked through a critical point by quantum phase transition, in the thermodynamic limit, are identified. The strong DM interaction delays quantum phase transition and hence shifts the boundary between the two phases to the region of the strong coupling constant. The increasing strength of the DM interaction strongly restores entanglement against its degradation arising from the increasing size of the system. The first derivative of the entanglement quantifier diverges to the critical point and is related directly to the divergence of the correlation length. The scaling behavior in the vicinity of the quantum critical point is also discussed.

Minimal radius of magnetic skyrmions: statics and dynamics

In a broad range of applied magnetic fields and material parameters isolated magnetic skyrmions condense into skyrmion lattices. While the geometry of isolated skyrmions and their lattice counterparts strongly depend on field and Dzyaloshinski–Moriya interaction, this issue has not been adequately addressed in previous studies. Meanwhile, this information is extremely important for applications, because the skyrmion size and the interskyrmion distance have to be tuned for skyrmion based memory and logic devices. In this investigation we elucidate the size and density-dependent phase diagram showing traditional phases in field versus material parameters space by means of Monte-Carlo simulations on a discrete lattice. The obtained diagram permits us to establish that, in contrast to the continuum limit, skyrmions on a discrete lattice cannot be smaller than some critical size and have a very specific shape. These minimal skyrmions correspond to the micromagnetic configuration at the energy barrier between the ferromagnetic and the skyrmionic states. Furthermore, we use atomistic Landau–Lifshitz–Gilbert simulations to study dynamics of the skyrmion annihilation. It is shown that this procees consists of two stages: the continuous skyrmion contraction and its discontinuous annihilation. The detailed analysis of this dynamical process is given.

Numerical studies on antiferromagnetic skyrmions in nanodisks by means of a new quantum simulation approach

We employ a new quantum simulation approach to study the magnetism of nanodisks with Dzyaloshinsky–Moriya (DM) interaction. We find that a weak external magnetic field normal to the disk plane cannot obviously affect the single AFM skyrmion structure on small disk; but if it is sufficiently strong, it can destroy the AFM skyrmion completely. By increasing DM interaction, more self-organized magnetic domains appear, the average distance of the neighboring domains agrees well with a grid theory. In this case, a magnetic anisotropy normal to the disk plane can re-construct AFM skyrmion, providing a way for experimentalists to create AMF skyrmions.

Effects of external magnetic field and magnetic anisotropy on chiral spin structures of square nanodisks investigated with a quantum simulation approach

We employed a quantum simulation approach to investigate the magnetic properties of monolayer square nanodisks with Dzyaloshinsky-Moriya (DM) interaction. The computational program converged very quickly, and generated chiral spin structures on the disk planes with good symmetry. When the DM interaction is sufficiently strong, multi-domain structures appears, their sizes or average distance between each pair of domains can be approximately described by a modified grid theory. We further found that the external magnetic field and uniaxial magnetic anisotropy both normal to the disk plane lead to reductions of the total free energy and total energy of the nanosystems, thus are able to stabilize and/or induce the vortical structures, however, the chirality of the vortex is still determined by the sign of the DM interaction parameter. Moreover, the geometric shape of the nanodisk affects the spin configuration on the disk plane as well.

Effects of Dzyaloshinsky–Moriya interaction on magnetism in nanodisks from a self-consistent approach

We give a theoretical study on the magnetic properties of monolayer nanodisks with both Heisenberg exchange and Dzyaloshinsky–Moriya (DM) interactions. In particular, we survey the magnetic effects caused by anisotropy, external magnetic field, and disk size when DM interaction is present by means of a new quantum simulation method facilitated by a self-consistent algorithm based on mean field theory. This computational approach finds that uniaxial anisotropy and transversal magnetic field enhance the net magnetization as well as increase the transition temperature of the vortical phase while preserving the chiralities of the swirly magnetic structures, whereas when the strength of DM interaction is sufficiently strong for a given disk size, magnetic domains appear within the circularly bounded region, which vanish and give in to a single vortex when a transversal magnetic field is applied. The latter confirms the magnetic skyrmions induced by the magnetic field as observed in the experiments.

RKKY interaction for the spin-polarized electron gas

We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky–Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form [Formula: see text]. We find that for the spin-polarized electron gas, a nonzero tensor interaction [Formula: see text] is present in addition to the scalar RKKY interaction [Formula: see text], while [Formula: see text] is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta [Formula: see text] and [Formula: see text], while the [Formula: see text] distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.

Nuclear spin-lattice relaxation at field-induced level crossings in a Cr8F8 pivalate single crystal

We construct a microscopic theory for the proton spin-lattice relaxation-rate 1/T1 measurements around field-induced level crossings in a single crystal of the trivalent chromium ion wheel complex [Cr8F8(OOCtBu)16] at sufficiently low temperatures [E. Micotti et al., Phys. Rev. B 72 (2005) 020405(R)]. Exactly diagonalizing a well-equipped spin Hamiltonian for the individual clusters and giving further consideration to their possible interactions, we reveal the mechanism of 1/T1 being single-peaked normally at the first level crossing but double-peaked intriguingly around the second level crossing. We wipe out the doubt about poor crystallization and find out a solution—intramolecular alternating Dzyaloshinsky–Moriya interaction combined with intermolecular coupling of antiferromagnetic character, each of which is so weak as several tens of mK in magnitude.

Gapless quantum spin liquid ground state in the two-dimensional spin-1/2 triangular antiferromagnet YbMgGaO4.

Quantum spin liquid (QSL) is a novel state of matter which refuses the conventional spin freezing even at 0 K. Experimentally searching for the structurally perfect candidates is a big challenge in condensed matter physics. Here we report the successful synthesis of a new spin-1/2 triangular antiferromagnet YbMgGaO4 with symmetry. The compound with an ideal two-dimensional and spatial isotropic magnetic triangular-lattice has no site-mixing magnetic defects and no antisymmetric Dzyaloshinsky-Moriya (DM) interactions. No spin freezing down to 60 mK (despite θw ~ −4 K), the power-law temperature dependence of heat capacity and nonzero susceptibility at low temperatures suggest that YbMgGaO4 is a promising gapless (≤|θw|/100) QSL candidate. The residual spin entropy, which is accurately determined with a non-magnetic reference LuMgGaO4, approaches zero (<0.6%). This indicates that the possible QSL ground state (GS) of the frustrated spin system has been experimentally achieved at the lowest measurement temperatures.

Physical pressure and chemical expansion effects on the skyrmion phase in Cu2OSeO3

The effects of external (hydrostatic) compression and internal (chemical) expansion on the skyrmion phase have been investigated in Cu2OSeO3 single crystal and Cu2OSe1−xTexO3 (0 ⩽ x ⩽ 0.2) polycrystalline samples respectively. Under external pressure, the ferrimagnetic temperature TC ~ 57 K is increased with a positive rate (dTC /dP = 0.27 K kbar−1). The skyrmion zone enclosed in the H-T phase diagram is enlarged and shifted to high temperatures for Cu2OSeO3 single crystal. Consistently, the TC decreases with a negative rate (dTC /dx = −15.5 K/x) in Cu2OSe1−xTexO3 (0 ⩽ x ⩽ 0.2) and the skyrmion zone is suppressed and shifted to the low temperature side; complete disappearance of the skyrmion phase has been noted for x = 0.2. These observed results are explained to be related to the local crystal structure, namely, inter-atomic bond lengths and bond angles that modulate the strengths of competing Heisenberg exchange and Dzyaloshinsky–Moriya (DM) interactions. This approach to tuning the skyrmion ground state by external and chemical pressures might be useful for designing of spintronics devices.

Current and field driven domain wall motion under influence of the Dzyaloshinsky–Moriya interaction

AbstractA complete analytical description of the dynamics of current and field driven transverse domain walls under the influence of the Dzyaloshinsky–Moriya interaction using the q– model will be given. Five different scenarios will be observed where the Dzyaloshinsky–Moriya vector is either parallel or perpendicular to the easy axis anisotropy of the system and a direct reversal, respectively, precessional motion will be assumed.

Geometric phase and the influence of the Dzyaloshinski–Moriya interaction in the one-dimensional quantum compass model

Geometric phase and quantum phase transition (QPT) of the one-dimensional (1D) quantum compass model with the Dzyaloshinski–Moriya (DM) interaction are investigated, and the effect of the DM interaction to the properties of geometric phase and QPTs of the model are discussed in this paper. Our study is an extension of the relation between the geometric phase and QPTs in the 1D spin systems.

Optimal quantum communication transfer through two XXZ spin chains with three-site and Dzyaloshinsky–Moriya interactions

We investigate quantum entanglement transfer through two independent spin chains with three site and Dzyaloshinsky–Moriya interactions and the effect of phase shift. The initial target state |01+|10/2 or its mixed state is shown to be more suitable for quantum correlation transfer in this system. Although the three-site or Dzyaloshinsky–Moriya interaction can partially improve the transmission quality of quantum entanglement, it mainly enhances the amplitude rather than prolongs the survival time of entanglement. We find that strengthening the three-site interaction enhances the amplitude of quantum entanglement more significantly, and that of Dzyaloshinsky–Moriya interaction accelerates the entanglement vibration as time evolution more obviously.

Crystalline and spin chiralities in multiferroics with langasite-type structure and Fe1–x Co x Si crystals

It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the Neel point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector kz exceeds the magnetic helicoid wave vector by a factor of 2: kz = 2qz. The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature (ТU> ТМ), structural displacements may arise in the absence of magnetism at ТМ < Т < ТU. In noncentrosymmetric Fe1–xCoxSi crystals (sp. gr. P213), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski–Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

Exchange bias effect in CaMn0.9Nb0.1O3

The exchange bias effect in CaMn0.9Nb0.1O3 has been investigated. It was found that both vertical and horizontal shifts in magnetic hysteresis loop of field cooled sample decrease monotonously with increasing temperature and vanish above 70 K, while the coercivity disappears only above 90 K, upon approaching the Néel temperature. An exponential decay successfully describes variation of the shifts with temperature. The exchange bias phenomenon is in general attributed to low-temperature phase separation into ferromagnetic clusters immersed in the G-type or C-type antiferromagnetic matrix and the resulting appearance of interfaces between coexisting different magnetic phases. Our results indicate that the exchange bias effect in CaMn0.9Nb0.1O3 may be induced, at least partially, by Dzyaloshinsky–Moriya interactions. Measurements of hysteresis loops at various cooling fields from the range −90 < H < 90 kOe show that magnetization at magnetic field H > 20 kOe exhibits a nonlinear increase and a sort of metamagnetic transition that appears to be responsible for a complete suppression of the exchange bias effect in CaMn0.9Nb0.1O3 at high magnetic field.

Quantum teleportation in a three-qubit Heisenberg chain with Dzyaloshinsky–Moriya interaction

The quantum teleportation via thermally entangled states of three-qubit Heisenberg spin chains with Dzyaloshinsky–Moriya (DM) interactions under a homogeneous magnetic field has been investigated. It is found that average fidelity and critical temperature depend on not only temperature, magnetic field, but also coupling coefficients, and DM interactions. What is more, we also find that average fidelity has little to do with entanglement.

Electrical and magnetic properties of spherical SmFeO3 synthesized by aspartic acid assisted combustion method

Samarium orthoferrite (SmFeO3) is synthesized by a simple combustion method using aspartic acid as fuel. Phase purity and functional groups are analyzed via X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis, which confirms the single phase formation of orthorhombic SmFeO3. Approximately spherical particles with size range 150–300nm is revealed by scanning electron microscope (SEM). The conductivity of the material is identified by the single semicircle obtained in the solid state impedance spectra at elevated temperatures. The calculated electrical conductivity increases with increasing temperature, inferring the semiconducting nature of SmFeO3. A magnetic study at room temperature revealed weak ferromagnetic behaviour in SmFeO3 due to Dzyaloshinsky–Moriya antisymmetric exchange interaction mechanism. Mössbauer analysis confirmed the +3 oxidation state of iron and magnetic ordering of the sample at room temperature.

Dynamics of Measurement-Induced Non-Locality and Geometric Measure of Discord in a Two-Qubit Heisenberg XY Chain

By taking into account the Dzyaloshinsky-Moriya (DM) interaction under uniform magnetic field, quantum correlation behaviors measured by the measurement-induced nonlocality (MIN) and the geometric measure of discord (GMOD) in a two-qubit XY model are investigated in detail. Turning the different parameters can lead the two kinds of measurements to present different properties. For example, increasing the parameter B(uniform magnetic field), the existing region of MIN is larger than GMOD; MIN can appear the phenomenon of monotonous reduction when the parameter D(Dzyaloshinsky-Moriya interaction) is smaller than one threshold value, while GMOD cannot; MIN monotonously reduces with enhancive value of T(temperature), while GMOD initial experiences a slightly increasing and then decreases. One interesting point is that the more obvious and complicated difference between them are shown from the initial values. This property is both true for the zero temperature and the finite temperature. Through analyzing the limit case of the temperature approaching zero, the analytic solutions give the detailed reasons why have different effect on the initial values. Moreover, from the analytic solutions, we know the initial value of MIN is always larger than or equal to GMOD.

Effect of Dzyaloshinsky–Moriya interaction on magnetic vortex: A real-space phase-field study

A real-space phase field model is developed to investigate the effect of Dzyaloshinsky–Moriya (DM) interaction on magnetic vortex in ultrathin ferromagnetic film. Based on the time-dependent Ginzburg–Landau (TDGL) equation, the phase field model takes into account the DM interaction of magnetizations, which includes the coupling between the magnetization and magnetization gradient. The governing equations in the phase field model are solved simultaneously by means of a nonlinear finite elements method, which can be employed to simulate magnetization vortex without periodic boundary condition. The simulation results demonstrate that the DM interaction has significant influence on the structure of the magnetization vortex. It is found that the DM interaction induces an out-of-plane magnetization on the edge of the vortex and enlarges the size of the vortex core. The magnitude of the out-of-plane magnetization at the vortex core and the edge increases with the increase of DM constant. Besides, the handedness of magnetization vortex also changes when the sign of DM constant changes.