Dzyaloshinsky Moriya Research Articles

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.

Thermal quantum discord in Heisenberg models with Dzyaloshinski—Moriya interaction

We study the quantum discord of the bipartite Heisenberg model with the Dzyaloshinski-Moriya (DM) interaction in thermal equilibrium state and discuss the effect of the DM interaction on the quantum discord. The quantum entanglement of the system is also discussed and compared with quantum discord. Our results show that the quantum discord may reveal more properties of the system than quantum entanglement and the DM interaction may play an important role in the Heisenberg model.

LOSCHMIDT ECHO OF A CENTRAL SPIN COUPLED TO AN XY SPIN CHAIN WITH DZYALOSHINSKY–MORIYA INTERACTION

By introducing the Dzyaloshinsky–Moriya (DM) interaction, the Loschmidt Echo (LE) of a quantum system consisting of a central spin and its surrounding environment characterized by an XY spin chain was investigated. The analytical expression of the LE was obtained. The effects of magnetic field, DM interaction, spin chain size, and anisotropy parameter on the evolution behavior of the LE were discussed numerically. At the critical points of magnetic field, the LE presents an obvious decay following with local oscillation. The decaying and oscillation behavior of the LE can be tuned by the intensity of the DM interaction. With increasing the spin chain size, the decaying amplitude is increased and the following oscillation behavior vanishes for the spin chain with larger size. The effect of the anisotropy parameter on the LE presents different properties at both sides of the knee point. The effect of the DM interaction on the decay of the LE is also related to the value of anisotropy parameter.

Critical behavior of XY spin chain with Dzyaloshinsky–Moriya interaction studied in terms of Loschmidt echo

In this paper, the critical behavior of the general XY spin chain with the Dzyaloshinsky–Moriya (DM) interaction is studied by means of a Loschmidt Echo (LE) calculation. LE presents a Gauss decay in the region of magnetic field intensity |λ|<1 and an exponential decay in the region of |λ|>1. There exists a critical spin chain size NC. When spin chain size is larger than NC, the value of λ corresponding to the minimum value of LE (λm) is independent of the spin chain size and keeps a stable value. In the region of λ<0, the stable value is same for different DM interactions. In the region of λ>0, the stable value varies with changing DM interaction.

Measurement-induced disturbance and thermal entanglement in spin models

Quantum correlation in two-qubit spin models is investigated by use of measurement-induced disturbance [S. Luo, Phys. Rev. A, 77 (2008) 022301]. Its dependences on external magnetic field, spin–spin coupling, and Dzyaloshinski–Moriya (DM) interactions are presented in detail. We also compare measurement-induced disturbance and thermal entanglement in spin models and illustrate their different characteristics.

Yangian symmetry in molecule {V6} and four-spin Heisenberg model

The symmetry operator Q = Y 2 is introduced to re-describe the Heisenberg spin triangles in the {V6} molecule, where Y stands for the Yangian operator which can be viewed as special form of Dzyaloshinsky–Moriya (DM) interaction for spin 1/2 systems. Suppose a parallelogram Heisenberg model that is comprised of four 1 2 -spins commutes with Q, which mean that it possesses Yangian symmetry, we show that the ground state of the Hamiltonian H 4 for the model allows to take the total spin S = 1 by choosing some suitable exchange constants in H 4. In analogy to the molecule {V6} where the two triangles interact through Yangian operator we then give the magnetization for the theoretical molecule “{V8}” model which is comprised of two parallelograms. Following the example of molecule {V15}, we give another theoretical molecule model regarding the four 1 2 -spins system with total spin S = 1 and predict the local moments to be 9 10 μ B , 1 10 μ B , 1 10 μ B , 9 10 μ B , respectively.

Pairwise thermal entanglement in a three-qubit Heisenberg XX model with a nonuniform magnetic field and Dzyaloshinski—Moriya interaction

Pairwise thermal entanglement in a three-qubit Heisenberg XX model is investigated when a nonuniform magnetic field and the Dzyaloshinski—Moriya interaction are included. We find that the nonuniform magnetic field and Dzyaloshinski—Moriya interaction are the more efficient control parameters for the increase of entanglement and critical temperature. For both the nearest neighbour sites and the next nearest neighbour sites, the magnetic field can induce entanglement to a certain extent and the Dzyaloshinski—Moriya interaction can enhance the entanglement to a stable value. The steady value of the nearest neighbour site entanglement C12 is larger than the next nearest neighbour site entanglement C13. An interesting phenomenon is that the entanglement curve of C12 appears a peak value when the Dzyaloshinski—Moriya interaction is considered in a nonuniform magnetic field.

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.

Teleportation and thermal entanglement in two-qubit Heisenberg XYZ spin chain with the Dzyaloshinski–Moriya interaction and the inhomogeneous magnetic field

This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg XYZ chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski–Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski–Moriya interaction for the average fidelity of teleportation to be optimal.

Magnetic relaxation in V 15 cluster: Direct spin-phonon transitions

In this article we propose a model of spin-vibronic relaxation in K 6[V IV 15As 6O 42(H 2O)]·8H 2O, the so called V 15 cluster exhibiting the unique layered structure. The work is motivated by the recent observation of the Rabi oscillation [1] in this system and aimed to elucidate the nature of the relaxation processes. The model assumes that the spin-phonon coupling arises as a result of modulation of the isotropic and antisymmetric (Dzyaloshinsky–Moriya) exchange interactions in the central triangular layer of vanadium ions by the acoustic lattice vibrations. Within the pseudo-angular momentum representation the selection rules for the direct (one-phonon) transitions between Zeeman levels are derived and a special role of the antisymmetric exchange is underlined. The relaxation times related to one-phonon transitions in different ranges of the field are estimated within the Debye model for the lattice vibrations.

Quantum phase transitions in single-crystalMn1−xFexSiandMn1−xCoxSi: Crystal growth, magnetization, ac susceptibility, and specific heat

We report the magnetization, ac susceptibility, and specific heat of optically float-zoned single crystals of ${\text{Mn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}\text{Si}$ and ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$ for temperatures down to $\ensuremath{\sim}2\text{ }\text{K}$ and magnetic fields up to 9 T. The suppression of the helimagnetic transition temperature ${T}_{1}$ above a critical composition ${x}_{1}$, as seen in the magnetization, ac susceptibility, and specific heat, suggests the existence of a quantum phase transition at ${x}_{1}$. A Vollhardt invariance at a temperature ${T}_{2}&gt;{T}_{1}$, which may be attributed to the Dzyaloshinsky-Moriya (DM) spin-orbit interactions, is also suppressed with increasing $x$ and vanishes above a concentration ${x}_{2}$, where ${x}_{2}&gt;{x}_{1}$. When suppressing the effects of the DM interactions in an applied magnetic field, the magnetization for sufficiently large fields shares the signatures expected of an underlying putative ferromagnetic quantum critical point for a critical concentration ${x}_{c}$, where ${x}_{1}&lt;{x}_{c}&lt;{x}_{2}$. As a function of normalized concentration $x/{x}_{c}$, where ${x}_{c}^{\text{Co}}\ensuremath{\approx}0.084$ and ${x}_{c}^{\text{Fe}}\ensuremath{\approx}0.192$, the properties of ${\text{Mn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}\text{Si}$ and ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$ are essentially identical with ${x}_{1}/{x}_{c}\ensuremath{\approx}0.78$ and ${x}_{2}/{x}_{c}\ensuremath{\approx}1.17$. Taken together, our study identifies ${\text{Mn}}_{1\ensuremath{-}x}{\text{Fe}}_{x}\text{Si}$ and ${\text{Mn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{Si}$ as model systems in which the influence of DM interactions on ferromagnetic quantum criticality may be studied.

Elementary excitations and specific heat in quantum sine-Gordon spin chain KCuGaF 6

Elementary excitations of an S=1/2 antiferromagnetic Heisenberg chain KCuGaF 6 were investigated through specific heat and electron spin resonance (ESR) measurements. In this compound, a staggered field is induced perpendicular to the external field because of the alternating g tensor and the Dzyaloshinsky–Moriya interaction with an alternating D vector. Such a spin system can be mapped onto the quantum sine-Gordon (SG) model, when subjected to the external magnetic field. Specific heat shows clear evidence of the field-induced gap, which is related to the elementary excitations, solitons and breathers, characteristic of the quantum SG model. q=0 excitations originated from solitons and breathers were directly observed by high-frequency high-field ESR. These experimental results are well described by the quantum SG field theory.

Entanglement in the Heisenberg spin chain with multiple interaction

The ground state and thermal entanglement of a Heisenberg spin chain in the presence of the multiple coupling interaction (type of XZX+ YZY and type of XZY− YZX) is investigated. It is found that the role of the type of XZY− YZX interaction to the entanglement is identical to the Dzyaloshinsky–Moriya interaction. For a XZX+ YZY type three-site interaction, the results show that this interaction can excite and enhance the entanglement even at the higher temperature.

Isothermal remanent magnetization and the spin dimensionality of spin glasses

The isothermal remanent magnetization is used to investigate dynamical magnetic properties of spatially three-dimensional spin glasses with different spin dimensionality (Ising, XY, Heisenberg). The isothermal remanent magnetization is recorded versus temperature after the application of a weak magnetic field at a constant temperature T h . We observe that in the case of the Heisenberg spin glasses, the equilibrated spin structure and the direction of the excess moment are recovered at T h . The isothermal remanent magnetization thus reflects the directional character of the Dzyaloshinsky–Moriya interaction present in Heisenberg systems.

Disentanglement dynamics of interacting two qubits and two qutrits in an XY spin-chain environment with the Dzyaloshinsky–Moriya interaction

We investigate disentanglement dynamics of two coupled qubits and qutrits which interact uniformly to a general XY spin-chain environment with the Dzyaloshinsky–Moriya (DM) interaction. We obtained exact expression of the time evolution operator and analyzed the dynamical process of the decoherence factors. Through explicitly calculating the concurrence and the negativity, we examined disentanglement behaviors of two coupled central spins evolve from different initial pure states, which are found to be nontrivially different from those of the uncorrelated ones, in particular, the enhanced decay of the entanglement induced by quantum criticality of the surrounding environment may be broken by introducing self-Hamiltonian of the central spin system. Moreover, the DM interaction may have different influences on decay of the entanglement depending on the strength of the system–environment coupling, the anisotropy of the environmental spin chain and the intensity of the transverse magnetic field, as well as the explicit form of the initial states of the central spin system.

Concurrence of finite Ising chains with the Dzyaloshinsky–Moriya interaction

Due to the great impact that quantum information theory has and its applicability for condensed matter systems, we study the concurrence measure of entanglement for the finite Ising chain with the Dzyaloshinsky–Moriya interaction. The explicit calculation of the concurrence and the reduced density matrix necessary to calculate it is presented, in order to use them as a pedagogical tool to make such important concepts clearer. A growth of the concurrence was observed as the parameter of the interaction increased, reaching a maximum at D = 1, which indicates the phase transition of the system from an antiferromagnetic phase to a chiral one.

Geometric phases and quantum phase transitions in inhomogeneous XY spin-chains: Effect of the Dzyaloshinski–Moriya interaction

We study geometric phases of the ground states of inhomogeneous XY spin chains in transverse fields with Dzyaloshinski–Moriya (DM) interaction, and investigate the effect of the DM interaction on the quantum phase transition (QPT) of such spin chains. The results show that the DM interaction could influence the distribution of the regions of QPTs but could not produce new critical points for the spin-chain. This study extends the relation between geometric phases and QPTs.

The entanglement dynamics of interacting qubits embedded in a spin environment with Dzyaloshinsky-Moriya term

We investigate the entanglement dynamics of two interacting qubits in a spin environment, which is described by an XY model with Dzyaloshinsky-Moriya (DM) interaction. The competing effects of environmental noise and interqubit coupling on entanglement generation for various system parameters are studied. We find that the entanglement generation is suppressed remarkably in weak-coupling region at quantum critical point (QCP). However, the suppression of the entanglement generation at QCP can be compensated both by increasing the DM interaction and by decreasing the anisotropy of the spin chain. Beyond the weak-coupling region, there exist resonance peaks of concurrence when the system-bath coupling equals to external magnetic field. We attribute the presence of resonance peaks to the flat band of the self-Hamiltonian. These peaks are highly sensitive to anisotropy parameter and DM interaction.

Novel Ordered Phases in the Orthogonal Dimer Spin System SrCu2(BO3)2

The magnetic properties of SrCu 2 (BO 3 ) 2 , a model spin system on the two-dimensional (2D) Shastry–Sutherland lattice, are reviewed with particular emphasis on the nuclear magnetic resonance (NMR) experiments. SrCu 2 (BO 3 ) 2 has a dimer singlet ground state at zero magnetic field and shows a sequence of magnetization plateaux at high magnetic fields. The plateaux are attributed to the localization of triplets into a superlattice due to mutual repulsion. Such a superstructure has been indeed observed at the 1/8 plateau by NMR experiments. Furthermore, the superstructure persists above the 1/8 plateau, where new phases have been identified by the torque and NMR measurements. SrCu 2 (BO 3 ) 2 also has the anisotropic Dzyaloshinski–Moriya interactions, which significantly change the ground state in magnetic fields. A recent development is the discovery of a new magnetic phase transition under high pressure. At 2.4 GPa, the 11 B NMR spectrum exhibits line splitting as a function of temperature in two steps. A gradual splitting below 30 K indicating loss of four-fold symmetry is followed by a further sudden splitting below 4 K marking a clear magnetic phase transition. The low- T phase has a doubled unit cell, yet with no spontaneous magnetic moment. A new type of valence-bond-solid (VBS) order is proposed.

Entanglement dynamics from quantum critical environment: Role of Dzyaloshinsky–Moriya interaction

We investigate the temporal evolution of entanglement of three spin qubits coupled to an XY spin-chain with Dzyaloshinsky–Moriya (DM) interaction environment. For an initial state with W, we find that the DM interaction can enhance slightly the decay of entanglement both in the weak coupling region and strong coupling one. However, for an initial state with GHZ, the decay of entanglement is very sensitive to the DM interaction in the strong coupling region.