Antisymmetric Dzyaloshinsky-Moriya Research Articles

The orbital effect on the anomalous magnetism and evolution in LaxY1-xVO3 (0 ≤ x ≤ 0.2) single crystals

The orbital effect on the anomalous magnetism and evolution of single crystals with low La doping, LaxY1−xVO3 (x = 0, 0.1, and 0.2), has been studied using single-crystal X-ray diffraction, specific heat, magnetization, and Raman-scattering techniques. It is found that substituting Y3+ by La3+ increases the degeneracy of the yz/zx orbitals and decreases the Jahn-Teller distortion. These weakens the G-type (antiphase ordering along the c axis) orbital ordering phase. Meanwhile, the substituting decreases the magnetism entropy, indicating the shrinking of the t2g and eg orbital hybridization, eventually destabilizing the C-type (in-phase ordering along the c axis) antiferromagnetic ordering phase. In addition, the mechanism for the shrinking of the diamagnetism with increasing x is analyzed. It may attribute to the competition between the antisymmetric Dzyaloshinsky–Moriya interaction and the single-ion anisotropy.

Origin of Multiferroism of β-NaFeO2

The multiferroic β-NaFeO2 is theoretically investigated for the first time using a microscopic model and Green’s function technique. A small room-temperature ferromagnetism is observed, which could be explained by canting of the antiferromagnetic sublattices. The ferromagnetic behaviour can be applied to applications in spintronic devices. We have investigated the temperature and magnetic field dependence of the spontaneous polarization Ps, as calculated from the transverse Ising model and the spin-assisted polarization ΔP due to magnetostriction and antisymmetric Dzyaloshinsky–Moriya interactions. The influence of external magnetic fields along the y and z axis is discussed. This is indirect evidence for the multiferroic behaviour of NaFeO2. The temperature dependence of the relative dielectric permittivity is calculated.

Size dependence of magnetic and dielectric properties in YCr0.5Fe0.5O3 ceramics

The YCr0.5Fe0.5O3 ceramics with different sintering temperatures (TS) have been synthesized by a sol-gel method, and the structural, magnetic and dielectric properties are studied. With the decrease of TS, continuous decrease of grain size is evidenced via the micromorphology analysis. Due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky-Moriya interaction, the total magnetization becomes zero at the compensation temperature (TComp) in the presence of a lower magnetic field, and the TComp exhibits size dependent behavior. With the decrease of grain size, the TComp becomes lower due to the increase of uncompensated spins. Meanwhile, the TComp is adjustable by the magnetic field, and a larger external field drives the TComp to lower temperature. After cooling the samples in magnetic field, the magnetic anisotropy is established, which results in a positive exchange bias (EB) effect below the TComp. The decrease of TS would increase the ferromagnetic component, which leads to the decrease of EB field (HEB). The dielectric measurements suggest that the samples of TS = 900 and 800 °C possess large permittivity accompanied with dielectric relaxation near room temperature, and the dielectric relaxation which arises from the single-ionized oxygen vacancies moves to higher temperature with the decrease of TS.

On the quantum correlations in two-qubit XYZ spin chains with Dzyaloshinsky–Moriya and Kaplan–Shekhtman–Entin-Wohlman–Aharony interactions

The anisotropic Heisenberg two-spin-1/2 model in an inhomogeneous magnetic field with both antisymmetric Dzyaloshinsky-Moriya and symmetric Kaplan-Shekhtman-Entin-Wohlman-Aharony cross interactions is considered at thermal equilibrium. Using a group-theoretical approach, we find fifteen spin Hamiltonians and as many corresponding Gibbs density matrices (quantum states) whose eigenvalues are expressed only through square radicals. We also found local unitary transformations that connect nine of this fifteen state collection, and one of them is the X quantum state. Since such quantum correlations as quantum entanglement, quantum discord, one-way quantum work deficit, and others are known for the X state, this allows to get the quantum correlations for any member from the nine state family. Further, we show that the remaining six quantum states are separable, that they are also connected by local unitary transformations, but, however, now the case with known correlations beyond entanglement is generally not available.

Room-temperature magnetization reversal and magnetocaloric switching in Fe substituted GdMnO3

Room-temperature tunable bipolar magnetization switching and magnetically switchable magnetocaloric phenomena having numerous application potentials are reported in $\mathrm{GdM}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{F}{\mathrm{e}}_{x}{\mathrm{O}}_{3}$ ($x=0.55$ and 0.60) polycrystalline samples. Substitution of Fe in antiferromagnetic $\mathrm{GdMn}{\mathrm{O}}_{3}$ induces a first-order spin-reorientation transition $({T}_{SR})$, which along with antiferromagnetic ordering transition $({T}_{\mathrm{N}})$ gives rise to anomalies in dielectric spectra, a signature of magnetodielectric effect. Temperature-dependent Raman spectra confirm the spin-phonon coupling which could be the origin of the magnetodielectric effect in the system. Notably, low-field magnetically tunable magnetization reversal is found to appear between ${T}_{\mathrm{SR}}$ and ${T}_{\mathrm{N}}$ in these compounds owing to the competition between single-ion magnetic anisotropy and antisymmetric Dzyaloshinsky-Moriya interaction. Additionally, the $\mathrm{GdM}{\mathrm{n}}_{0.40}\mathrm{F}{\mathrm{e}}_{0.60}{\mathrm{O}}_{3}$ sample reveals the coexistence of magnetically switchable conventional and inverse magnetocaloric effect at 250 and 310 K. The tailoring of these coexisting room-temperature magnetization reversal and magnetocaloric phenomena in a single-phase system suggests a route to design the material suitable for potential applications in electromagnetic and memory devices.

Positive exchange bias effect in LaCr0.5Fe0.5O3 perovskite

This work reports the synthesis and characterization of perovskites with LaCr0.5Fe0.5O3 stoichiometry. The perovskite was synthesized by an alternative route to traditional sol-gel method, the precursor was prepared using gelatin as a chelating agent and further calcined 2 h at 1200 °C. The sample is investigated by combining X-ray diffraction, Mössbauer spectroscopy and scanning electron microscopy with chemical microanalysis. The Rietveld refinement showed the formation of the La(OH)3 secondary phase in addition to the main perovskite phase. The M-T measurements showed a negative field cooling magnetization with a compensation temperature depending on the cooling field. The findings in the M-T measurements are discussed in terms of competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky-Moriya interactions. The M-H measurement at 300 K revealed a hysteretic behavior ascribed to ferromagnetic clusters. At low temperature the field cooling M-H curves showed a positive exchange bias field and a downward shift of the hysteresis. The shifting of the hysteresis and the exchange bias field began at 250 K, a bit below the Néel transition. The hysteresis shift is ascribed to an antiferromagnetic coupling between the ferromagnetic clusters and the antiferromagnetic LaCr0.5Fe0.5O3 phase.

Complex magnetic order in the Nd(Tb)Fe3(BO3)4 multiferroic revealed by single-crystal neutron diffraction

Magnetic structure of the substituted multiferroics-ferroborates ${\mathrm{Nd}}_{0.9}{\mathrm{Tb}}_{0.1}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ and ${\mathrm{Nd}}_{0.8}{\mathrm{Tb}}_{0.2}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ were determined in the framework of a self-consistent refinement of the single crystal neutron diffraction data. The small substitution of Nd for Tb leads to the reorientation of the main antiferromagnetic vector L from the basal plane towards the hexagonal axis. The reorientation takes place via an angular structure for which L does not coincide with the principal crystallographic directions and evolves with temperature due to competing magnetic anisotropies of Fe, Nd, and Tb subsystems. Our refinement at 2 K reveals the existence of distortions in the collinear antiferromagnetic Fe spin arrangement suggested before in other ferroborates. Therefore, besides the main antiferromagnetic vector L, the magnetic structure involves additional fine symmetrized combinations of spin components allowed by symmetry. They coexist with certain L components and could originate from the antisymmetric Dzyaloshinsky-Moriya Fe-Fe exchange interactions. At higher temperatures, the magnetic structure is described by the simple collinear model, where the L vector is deviated from the hexagonal plane.

Investigation of Co6(OH)3(TeO3)4(OH)~0.9(H20): Synthesis, crystal and magnetic structures, magnetic and dielectric properties

We have re-investigated the synthesis and the crystal structure of the non-centrosymmetric phase Co6(OH)3(TeO3)4(OH) published by Perez et al. in 1975 and we have obtained by hydrothermal synthesis the hydrated phase Co6(OH)3(TeO3)4(OH)~0.9(H20). The crystal structure related to the Ellenbergerite mineral was determined using single-crystal X-ray diffraction data. The non-centrosymmetric hexagonal structure (P63mc; a = 13.1640(7) Å; c = 5.0321(6) Å) is based on [CoO6] octahedra and [TeO3] polyhedra which formed a tunnel framework with a formal charge 1+ balanced by one OH- group located in large tunnels. Compared to Co6(OH)3(TeO3)4(OH) case we succeeded in locating the hydrogen atoms of the OH- groups bound to the Co and showed that a small amount of water resides also in the large tunnels with the OH- groups. The presence of water molecules was confirmed by infrared spectroscopy and thermogravimetric analyses. This phase behaves as a canted antiferromagnet below TN = 75.5 K. The average magnetic structure was solved from powder neutron diffraction. Antisymmetric Dzyaloshinsky-Moriya interactions in the (ab) plane have been highlighted and must be responsible for the spin canted antiferromagnetic ground state. Moreover, DFT calculations with an Ising model show the presence of a frustrated spin state for the two Co2+ cations involved in the antisymmetric Dzyaloshinsky-Moriya interaction. Under an applied magnetic field, a metamagnetic-like behaviour is observed with three different canted antiferromagnetic states. At low temperature, dielectric measurements evidence a magneto-structural coupling but no measurable magnetocapacitance.

Symmetric spin–orbit interaction in triple quantum dot and minimisation of spin–orbit leakage in CNOT gate

We analyse spin–orbit interaction in triple quantum dots and show that a symmetric spin–orbit Hamiltonian does not follow the standard form used in double quantum dots, as a consequence of the presence of the third dot in the setup. Furthermore, CNOT implementation schemes based on the exchange interaction were studied. It was shown that an antisymmetric Dzyaloshinsky–Moriya term is the dominant source of spin–orbit leakage from the computational space. We present a simple scheme for the minimisation of leakage that can be implemented in cases where interacting spins enclose parallelogram or equilateral triangle loops.

Magnetization reversal in Bi5Ti3Co0.5Fe0.5O15 ceramics

Here we report the structural, magnetic and dielectric properties of polycrystalline Bi5Ti3Co0.5Fe0.5O15 ceramic compounds. The samples annealed at 1073, 1173, and 1273 K were prepared by a modified Pechini process. XRD patterns of the samples show a single phase with a four-layered Aurivillius structure. The XPS analysis reveals that the oxygen vacancies increase with the sintering temperature. Temperature-induced magnetization reversal is observed around 133 and 127 K in a field-cooled mode with an applied field of 50 Oe in the samples sintered at 1173 and 1273 K, respectively. We identify that the magnetization reversal in these oxides originates from the competition between single-ion magnetic anisotropy and antisymmetric Dzyaloshinsky-Moriya interaction. In addition, we have also observed that the dielectric constant and loss tangent are enhanced by increasing sintering temperature. Both the appearance of magnetic reversal and the rising dielectric loss tangent are induced by the intensified distortion of the lattice structure due to the increment of oxygen vacancies as the increase in the sintering temperature.

Quantum coherence of the Heisenberg spin models with Dzyaloshinsky-Moriya interactions

We study quantum coherence in a spin chain with both symmetric exchange and antisymmetric Dzyaloshinsky-Moriya couplings. Quantum coherence is quantified using the recently introduced quantum Jensen-Shannon divergence, which has the property that it is easily calculable and has several desirable mathematical properties. We calculate exactly the coherence for arbitrary number of spins at zero temperature in various limiting cases. The σzσz interaction tunes the amount of coherence in the system, and the antisymmetric coupling changes the nature of the coherence. We also investigate the effect of non-zero temperature by looking at a two-spin system and find similar behavior, with temperature dampening the coherence. The characteristic behavior of coherence resembles that of entanglement and is opposite to that of discord. The distribution of the coherence on the spins is investigated and found that it arises entirely due to the correlations between the spins.

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.

Studies on (Sr1−xCax) MnO3 (0.0≤x≤1.0) ceramics having negative magnetization

This paper describes the structural and magnetic properties of the (Sr1−xCax) MnO3 (0.0≤x≤1.0) ceramics in bulk form synthesized by the chemical co-precipitation method. We observed that the increase in calcium concentration in strontium manganite changes the crystal symmetry from monoclinic to orthorhombic. The (Sr1−xCax) MnO3 (0.0≤x≤1.0) ceramic shows negative magnetization below ~42K; above this temperature it shows paramagnetic nature and below this it shows antiferromagnetic nature. Negative magnetization in this oxide seems to result from a competition between single-ion magneto crystalline anisotropy and antisymmetric Dzyaloshinsky–Moriya interactions.

Canted antiferromagnetism and spin reorientation transition in layered inorganic–organic perovskite (C6H5CH2CH2NH3)2MnCl4

This work presents the synthesis, structure determination and magnetic properties of a new complex, phenethylammonium tetrachloromanganate(II), (C(6)H(5)CH(2)CH(2)NH(3))(2)MnCl(4) (Mn-PEA). Single crystals of Mn-PEA were obtained from methanol solution using the solvent-evaporation method at room temperature. The crystal structure of Mn-PEA was determined by single-crystal X-ray diffraction (orthorhombic, space group Pbca, a = 7.2075(9), b = 7.3012(14), c = 39.413(6) Å and Z = 4). The structure consisted of an extended [MnCl(4)](2-) network and two phenethylammonium cations to form a two-dimensional halide perovskite structure. Temperature-dependent magnetization measurements indicated that Mn-PEA acted as a weak ferromagnet below T(C) = 44.3 K due to spin canting. Below T(C), the magnetic behavior differed significantly from the behavior commonly observed among weak ferromagnets. The susceptibility depended strongly on the crystal orientation, the external magnetic field strength, and the magnetic history. The isothermal magnetization for two orientations revealed a ferromagnetic moment with a spin-canting angle of 0.04° and a spin-flop transitions with H(sf) = 3.5 T. The weak ferromagnetism, which manifested as spontaneous magnetization and magnetic hysteresis near a field strength of zero, was driven by interplay between the easy axis and the antisymmetric Dzyaloshinsky-Moriya (DM) interaction, leading to directional dependent magnetic behavior.

Temperature- and magnetic-field-induced magnetization reversal in perovskite YFe0.5Cr0.5O3

Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky–Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.

Interplay of RKKY, Zeeman, and Dzyaloshinskii-Moriya interactions and the nonzero average spin chirality in Dy/Y multilayer structures

Metal magnetic/nonmagnetic (Dy/Y) multilayer structures posses a coherent spin helix propagating through many Dy/Y bilayers. Samples of different Dy and Y layer thicknesses were investigated using polarized neutron scattering to determine the average chirality of the magnetic structure. The in-plane applied magnetic field induces the chirality since it couples to the uncompensated moments of the helix in a Dy layer. The value of the chirality has a complex behavior in dependence on the temperature and the magnetic field. It is shown that the chirality is affected by the competition between the Ruderman-Kittel-Kasuya-Yoshida interactions of the intralayer exchange within the Dy layers and the interlayer coupling across the nonmagnetic Y layers. The set of the experimental data allows one to make the reconstruction and schematic visualization of the spin structure within the multilayer system. In spite of a complex dependency of the average chirality on the temperature and the magnetic field, the twist angle between the spin planes of two neighboring Y/Dy interfaces has the same sign for all samples at any conditions. It is antisymmetric Dzyaloshinsky-Moriya interaction that reveals itself through the sign of this twist angle and as a result through the nonzero average chirality of the magnetic multilayer structure.

Temperature-induced magnetization reversal inBiFe0.5Mn0.5O3synthesized at high pressure

${\text{BiFe}}_{0.5}{\text{Mn}}_{0.5}{\text{O}}_{3}$ could be stabilized in the perovskite structure by preparing it under high pressure and temperature. It has an orthorhombic structure with a possible ordered arrangement of Fe and Mn double rows and shows a magnetic ordering at high temperature (270 K). Low-temperature isothermal-magnetization measurements indicate the ground state to be antiferromagnetic with a spin canting. Surprisingly, it exhibits magnetization reversal at low applied fields below a compensation temperature, ${T}^{\ensuremath{\ast}}$. Below ${T}^{\ensuremath{\ast}}$, the sign of the magnetization can be switched between negative and positive value reversibly by increasing and decreasing the field. Magnetization reversal in this oxide seems to result from a competition between single-ion magnetocrystalline anisotropy and antisymmetric Dzyaloshinsky-Moriya interactions.

Tunneling and inversion symmetry in single-molecule magnets: The case of theMn12wheel molecule

We present a detailed study of the influence of various interactions on the spin quantum tunneling in a Mn12 wheel molecule. The effects of single-ion and exchange (spin-orbit) anisotropy are first considered, followed by an analysis of the roles played by secondary influences, e.g. disorder, dipolar and hyperfine fields, and magnetoacoustic interactions. Special attention is paid to the role of the antisymmetric Dzyaloshinski-Moriya (DM) interaction. This is done within the framework of a 12-spin microscopic model, and also using simplified dimer and tetramer approximations in which the electronic spins are grouped in 2 or 4 blocks, respectively. If the molecule is inversion symmetric, the DM interaction between the dimer halves must be zero. In an inversion symmetric tetramer, two independent DM vectors are allowed, but no new tunneling transitions are generated by the DM interaction. Experiments on the Mn12 wheel can only be explained if the molecular inversion symmetry is broken, and we explore this in detail using both models, focussing on the asymmetric disposition and rounding of Berry phase minima associated with quantum interference between states of opposite parity. A remarkable behavior exists for the `Berry phase zeroes' as a function of the directions of the internal DM vectors and the external transverse field. A rather drastic breaking of the molecular inversion-symmetry is required to explain the experiments; in the tetramer model this requires a reorientation of the DM vectors on one half of the molecule by nearly 180 degrees. This cannot be attributed to sample disorder. These results are of general interest for the quantum dynamics of tunneling spins, and lead to some interesting experimental predictions.

The incommensurate magnetic structure of a tetragonal antiferromagnet with antisymmetric exchange

Analysis of the incommensurate magnetic structure that emerges for two coexisting types of the antisymmetric Dzyaloshinski-Moriya exchange interaction (the weakly ferromagnetic component of vector D along the tetragonal axis and the helicoidal component distributed in the tetragonal plane) is carried out for the first time for a tetragonal antiferromagnet. The helicoidal component for each pair of interacting spins has a 2D distribution; its direction in the tetragonal plane depends on the direction of the exchange bond in each pair. The Lifshits invariant of the Ginzburg-Landau functional is obtained, which is responsible for the formation of an incommensurate magnetic structure for such a distribution. It is shown in the mean field approximation that the incommensurate magnetic structure that forms in this case is a nonlinear double helicoid with a modulation vector lying in the tetragonal plane and with a varying angle between the polarization planes of quasi-antiferromagnetic sublattices. The ground state of the magnet is degenerate in the orientation of the modulation vector in the tetragonal plane. The rate of variation in the orientations of moments in the polarization planes passing through the tetragonal axis is controlled by the angle between the directions of the moments and the tetragonal axis. The local weakly ferromagnetic moment remaining in the polarization plane varies in magnitude and sign. The relation between the orientations of the modulation and polarization vectors is derived for the cases of simple and inversion tetragonal axes in the space symmetry group of the crystal.

Superexchange interactions in orthorhombically distorted titanates RTiO3 (R = Y, Gd, Sm and La)

Starting from the multiorbital Hubbard model for the t2g-bands of RTiO3 (R=Y, Gd, Sm and La), where all the parameters have been derived from the first-principles electronic structure calculations, we construct an effective superexchange (SE) spin model, by treating transfer integrals as a perturbation. We consider four approximations for the SE interactions: (i) the canonical crystal-field (CF) theory, where the form of the occupied t2g-orbitals is dictated by the CF splitting at each Ti-site and three extensions of the CF theory, namely (ii) the relativistic one, where occupied orbitals are confined within the lowest Kramers doublet obtained from the diagonalization of the CF and relativistic spin–orbit (SO) interactions; (iii) the finite-temperature extension, which considers the effect of thermal orbital fluctuations near the CF configuration on interatomic interactions between the spins; (iv) the many-electron extension, which is based on the diagonalization of the full Hamiltonian constructed in the basis of two-electron states separately for each bond of the system. The main results are summarized as follows. (i) Thermal fluctuations of the orbital degrees of freedom can substantially reduce the value of the magnetic transition temperature. (ii) The relativistic SO coupling is generally responsible for anisotropic and antisymmetric Dzyaloshinsky–Moriya interactions. All interactions are rigorously derived and their implications for the magnetic properties of RTiO3 are discussed. (iii) The CF theory, although applicable for YTiO3 and high-temperature structures of GdTiO3 and SmTiO3, breaks down in the case of LaTiO3. In the latter, the CF splitting is small. Therefore, the many-electron effects in the bonds as well as the relativistic SO interaction start to play an important role. It is argued that the combination of these two effects could be responsible for the AFM character of interatomic correlations in LaTiO3. (iv) The SE interactions in YTiO3 strongly depend on the details of the crystal structure. Crystal distortions in the low-temperature structure tend to weaken the ferromagnetic interactions.