Temperature-driven spin reorientation transitionof magnetron sputtered nickel thin film

The temperature-driven spin reorientation transition of magnetron sputtered Ni/Si （111） systems has been studied. The relationship between ac initial susceptibility and temperature of nickel films with different thicknesses shows that the magnetization orientation changes from in-plane to out-of-plane with the increase of temperature. The temperature dependence of mugnetoelastic, magneto-crystalline, and magnetostatic anisotropies determines the direction of the reorientation transition. The temperature-driven spin reorientation transition is supported by Hall coefficient measurements which show that its temperature dependence is similar to that of susceptibility.     

Magnetocrystalline anisotropy and dynamic spin reorientation of half-doped Nd_(0.5)Pr_(0.5)FeO_3 single crystal

The single crystals of Nd_(0.5)Pr_(0.5)FeO_3 were successfully grown by optical floating zone method.Room temperature x-ray diffraction and Laue photograph declared the homogeneity and high quality of the crystal.The significant magnetic anisotropy and multiple magnetic transitions illustrate the complex magnetic structure.At high temperatures(T 66 K),it shows the typical characteristics of Γ_4(G_x,A_y,F_z) state.With the decrease of the temperature,it undergoes a first-order spin reorientation transition from Γ_4(G_x,A_y,F_z) to Γ_2(F_x,C_y,G_z) state in the temperature window of 45-66 K under an applied magnetic field of 0.01 T.As the temperature drops to ～17 K,a new magnetic interaction mechanism works,which results in a further enhancement of magnetization.The T-H phase diagram of Nd_(0.5)Pr_(0.5)FeO_3 single crystal was finally constructed.     

Quantum coherence and correlation dynamics of two-qubit system in spin bath environment

The quantum entanglement,discord,and coherence dynamics of two spins in the model of a spin coupled to a spin bath through an intermediate spin are studied.The effects of the important physical parameters including the coupling strength of two spins,the interaction strength between the intermediate spin and the spin bath,the number of bath spins and the temperature of the system on quantum coherence and correlation dynamics are discussed in different cases.The frozen quantum discord can be observed whereas coherence does not when the initial state is the Bell-diagonal state.At finite temperature,we find that coherence is more robust than quantum discord,which is better than entanglement,in terms of resisting the influence of environment.Therefore,quantum coherence is more tenacious than quantum correlation as an important resource.     

Entanglement and Teleportation via Thermally Entangled State of Anisotropic Heisenberg XYZ Chain with Inhomogeneous External Magnetic Field

In this paper we study the entanglement in a two-qubit spin in the XYZ model, and teleport a two-qubit entangled state using this spin chain in the condition of the thermal equilibrium as a quantum channel. We investigate the effects of the interaction of z-component Jz, the inhomogeneous magnetic field b, the anisotropy γ and the temperature T on the entanglement and fidelity. In order to characterize the quality of the teleported state, we research the average fidelity Fα. High average fidelity of the teleportation is obtained when the temperature is very low. Under some condition, we also find that when innomogeneity increases to a certain value, the average fidelity can exhibit a larger revival than that for less values of b.     

Spin excitations and spin wave gap in the ferromagnetic Weyl semimetal Co_3Sn_2S_2

We report a comprehensive neutron scattering study on the spin excitations in the magnetic Weyl semimetal Co3Sn2S2 with a quasi-two-dimensional structure.Both in-plane and out-of-plane dispersions of the spin waves were revealed in the ferromagnetic state.Similarly,dispersive but damped spin excitations were found in the paramagnetic state.The effective exchange interactions were estimated using a semi-classical Heisenberg model to consistently reproduce the experimental TCand spin stiffness.However,a full spin wave gap below Eg=2.3 meV was observed at T=4 K.This value was considerably larger than the estimated magnetic anisotropy energy(~0.6 meV),and its temperature dependence indicated a significant contribution from the Weyl fermions.These results suggest that Co3Sn2S2 is a three-dimensional correlated system with a large spin stiffness,and the low-energy spin dynamics can interplay with the topological electron states.     

Ground-State Entanglement and Mixture in an XXZ Spin Chain

We study the pairwise entanglement and mixture of a three-qubit XX Z spin chain in the ground state in the presence of an external magnetic field B. The effects of the magnetic field, the anisotropy and the temperature on the entanglement and mixture are considered, and entanglement versus the mixture of all the two-spin states is investigated. We find that the maximal entangled mixed state can be obtained in the considered system by controlling the magnetic field. Our results provide another way to generate maximally entangled mixed states.     

Magnetic Properties and Spin State Transition of Gallium Doped Perovskite Cobaltite Oxide

A series of Ga doping perovskite cobaltite La2/3Sr1/3 （Co1-y Gay）03 （y = 0, 0.1, 0.2, 0.3 and 0.4） are prepared by the standard solid-state reaction method. Their magnetic properties and Co ions spin state transitions are studied. Upon doping, no appreciable structure changes can be found. However, the corresponding Curie temperature sharply decreases and the magnetization is greatly reduced, indicating that Ga doping destroys the ferromagnetic interaction in the system. In addition, the high temperature magnetization data follow the Curie-Weiss law. At least one kind of Co ions （Co^3＋ or Co^4＋） favours the mixed spin state, and most Co ions are at the lower spin state （low and intermediate state）. With increasing Ga content, more Co ions transit to the higher spin state.     

MODELING AND SCALING OF CHIELECTRIC RELAXATION OF NONLINEAR OPTICAL POLYMERS IN FREQUENCY DOMAIN

chielectric relaxation theory was demonstrated, chielectric relaxation that selectively probes chromophore reorientation in the frequency domain was described by the Havriliak Negami(HN) function, chielectric spectra of several nonlinear optical (NLO) polymers were fitted well by the HN function. To describe the scaling of chromophore reorientation relaxation in frequency domain, two-shape parameters m and n describing the low- and high- frequency wings of the chielectric spectra need to be specified, besides the chielectric characteristic relaxation time τ and the chielectric strength Δχ⁽²⁾. From the temperature dependences of m and n of NLO polymers, the relations between the chromophore relaxation and the a relaxation of the polymer host have been revealed.     

Nonequilibrium dynamical phase transition of 3D kinetic Ising／Heisenberg spin system

We have studied the nonequilibrium dynamic phase transitions of both three-dimensional (3D) kinetic Ising and Heisenberg spin systems in the presence of a perturbative magnetic field by Monte Carlo simulation. The feature of the phase transition is characterized by studying the distribution of the dynamical order parameter. In the case of anisotropic Ising spin system (ISS), the dynamic transition is discontinuous and continuous under low and high temperatures respectively, which indicates the existence of a tri-critical point (TCP) on the phase boundary separating low-temperature order phase and high-temperature disorder phase. The TCP shifts towards the higher temperature region with the decrease of frequency, i.e. T_{TCP}=1.33×exp(-ω/30.7). In the case of the isotropic Heisenberg spin system (HSS), however, the situation on dynamic phase transition of HSS is quite different from that of ISS in that no stable dynamical phase transition was observed in kinetic HSS after a threshold time. The evolution of magnetization in the HSS driven by a symmetrical external field after a certain duration always tends asymptotically to a disorder state no matter what an initial state the system starts with. The threshold time τ depends upon the amplitude H_{0}, reduced temperature T/T_C and the frequency ω as τ=C·ω^α·H_0^{-β}·(T/T_C)^{-γ}.     

A study of magnetostriction,spin reorientation,and Mssbauer spectra of Tb_(0.3)Dy_(0.6)Pr_(0.1)(Fe_(1-x)Al_x)1.95 alloys with substitution of Fe by Al

The effects of Al substitution for Fe on the structure, magnetics, magnetostriction, anisotropy and spin reorientation of a series of Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95 alloys (x=0.05, 0.1, 0.15, 0.2, 0.25, 0.3) at room temperature have been investigated. The alloys of Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95 substantially retain MgCu2-type C-15 cubic Laves phase structure when x0.2. The mixed phases appear with x = 0.2, and cubic Laves phase decreases with increasing x. The magnetostriction of the Tb0.3Dy0.6Pr0.1(Fe1-xAlx)1.95 alloys decreases drastically with increasing x and the giant magnetostrictive effect disappears for x 0.15. Fortunately, a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. The spin reorientation temperature decreases with increasing x. The analysis of the Mssbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the increase of Al concentration x, namely, spin reorientation, resulting in the change of macroscopical magnetic properties and magnetostriction. The hyperfine field decreases, but the isomer shifts increases with Al concentration increasing and the quadruple splitting QS shows a weak concentration dependence.     

Temperature Effects of Parabolic Linear Bound Potential and Coulomb Bound Potential Quantum Dot Qubit

On the condition of electric-LO phonon strong coupling in a parabolic quantum dot, we obtain the eigenenergy and the eigenfunctions of the ground state and the first-excited state using the variational method of Pekar type. This system in a quantum dot may be employed as a two-level quantum system-qubit. When the electron is in the superposition state of the ground state and the first-excited state, we obtain the time evolution of the electron density. The relations of the probability density of electron on the temperature and the electron-LO-phonon coupling constant and the relations of the period of oscillation on the temperature, the electron-LO-phonon coupling constant, the Coulomb binding parameter and the confinement length are derived. The results show that the probability density of electron oscillates with a period when the electron is in the superposition state of the ground and the first-excited state, and show that there are different laws that the probability density of electron and the period of oscillation change with the temperature and the electron-LO-phonon coupling constant when the temperature is lower or higher. And it is obtained that the period of oscillation decreases with increasing the Coulomb bound potential and increases with increasing the confinement length not only at lower temperatures but also at higher temperatures.     

Critical temperature and condensed fraction of Bose-Einstein condensation in optical lattices

Critical temperature and condensate fraction of Bose-Einstein condensation in the optical lattice are studied. The results show that the critical temperature in optical lattices can be characterized with an equivalent critical temperature in a single lattice, which provide a fast evaluation of critical temperature and condensate fraction of Bose-Einstein condensation confined with pure optical trap. Critical temperature can be estimated with an equivalent critical temperature. It is predicted that critical temperature is proportional to q in q number lattices for superfluid state and should be equal to that in a single lattic for Mott insulate state. Required potential depth or Rabi frequency and maximum atom number in the lattices both for superfluid state and Mott state are presented based on views of thermal mechanical statistics.     

Characteristics of the spatiotemporal distribution of daily extreme temperature events in China: Minimum temperature records in different climate states against the background of the most probable temperature

Based on the skewed function,the most probable temperature is defined and the spatiotemporal distributions of the frequencies and strengths of extreme temperature events in different climate states over China are investigated,where the climate states are referred to as State I,State II and State III,i.e.,the daily minimum temperature records of 1961-1990,1971-2000,and 1981-2009.The results show that in space the frequency of high temperature events in summer decreases clearly in the lower and middle reaches of the Yellow River in State I and that low temperature events decrease in northern China in State II.In the present state,the frequency of high temperature events increases significantly in most areas over China except the north east,while the frequency of low temperature events decreases mainly in north China and the regions between the Yangtze River and the Yellow River.The distributions of frequencies and strengths of extreme temperature events are consistent in space.The analysis of time evolution of extreme events shows that the occurrence of high temperature events become higher with the change in state,while that of low temperature events decreases.High temperature events are becoming stronger as well and deserve to be paid special attention.     

Effect of cobalt on the magnetoresistance characteristics of rare-earth doped manganites

The effect of cobalt-doping on the magnetic, transport and magnetoresistance characteristics of La_1-xSr_xMnO₃ was investigated. The results show that the magnetoelectric property of rare-earth doped manganites is greatly affected by substitution of Co for Mn sites. The Curie temperature as well as the magnetic moment decreases with the increase of doping concentration, and the samples exhibit obvious characteristics of the spin glass state. Moreover, the magnetoresistance is evidently modulated by doping concentration, and the relevant temperature dependence is also suppressed. In addition, low-temperature magnetoresistance is significantly promoted as doping concentration increases, which renders a value of approximately 50% in the temperature range of 5--200~K and varies within 12.5%. It can be attributed to the effect of spin scattering, induced by cobalt doping, on the itinerant electrons of Mn ions, thus introducing a spin-disorder region into the ferromagnetic region of double-exchange interaction between neighbouring Mn³⁺ and Mn ³⁺ ions.     

High-dimensional quantum state transfer in a noisy network environment

We propose and analyze an efficient high-dimensional quantum state transfer protocol in an XX coupling spin network with a hypercube structure or chain structure. Under free spin wave approximation, unitary evolution results in a perfect high-dimensional quantum swap operation requiring neither external manipulation nor weak coupling. Evolution time is independent of either distance between registers or dimensions of sent states, which can improve the computational efficiency. In the low temperature regime and thermodynamic limit, the decoherence caused by a noisy environment is studied with a model of an antiferromagnetic spin bath coupled to quantum channels via an Ising-type interaction. It is found that while the decoherence reduces the fidelity of state transfer, increasing intra-channel coupling can strongly suppress such an effect. These observations demonstrate the robustness of the proposed scheme.     

Thermal entanglement in molecular spin rings

The thermal entanglement in the triangular molecular spin ring with Dzyaloshinskii-Moriya interaction is studied.The concurrences of arbitrary two spins of the triangular molecular spin ring for various cases are evaluated.The tendency of the concurrence with Dzyaloshinskii-Moriya interaction and temperature is analysed and discussed.We note that the concurrence arrives at its maximum in the regime with the large Dzyaloshinskii-Moriya interaction and low temperature,and gradually decreases to zero with the increase of temperature.The concurrence has different features for the ferromagnetic and antiferromagnetic cases.For completeness,we also numerically calculate the concurrence of spin rings with N > 3 spins and analyse their behaviours.     

Reorientation of Defect Dipoles in Ferroelectric Ceramics

We investigate the frequency, temperature, tetragonality and quenched temperature dependences of the hysteresis loops in Pb[(Zr0.52 Ti0.48)0.95 (Mn1/3Nb2/3)0.05]O3 (PMnN-PZT) ceramics. It has been demonstrated that the polarization-field hysteresis curves show “pinched” shapes when tested at room temperature, higher frequency or using the large-tetragonality specimen. While normal square-like loops are observed at 200℃ and 0.01 Hz or using the small-tetragonality one. Meanwhile, close relations between the P-E loops and the applied frequency,temperature or tetragonality reveal that there exists a typical relaxation time corresponding to the reorientation of the defect dipoles. It can be seen further from the quenched temperature dependences of the loops that the reorientation of the defect dipoles may influence the pinching. Compared to the intrinsic depinning procedure induced by changes of the distribution of defect dipoles, we provide new evidence for extrinsic depinning mechanism of the defect dipoles in the ferroelectric ceramics.     

Charge order and spin order in Nd0.5Sr0.5Mn1? x (Ga x , Ti x )O3 system

Magnetic properties of Nd0.5Sr0.5Mn1-x(Gax,Tix)O3 system (0.04≤x≤0.4) were investigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melting of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-Tcurves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.     

Flocking and clustering in mixtures of self-propelled particles with or without active reorientation

We study phase behaviors of mixtures comprising active particles with and without active reorientation by varying mixing ratios. We observe that the order parameter characterizing flocking in the steady state exhibits a linear decrease with an increase in mixing ratio. While the order parameter characterizing clustering in the steady state presents a sharp leap as the mixing ratio increases. Particularly, we obtain phase diagrams of flocking under different mixing ratios and observe that the dom...     

MAGNETIC PROPERTIES OF Pr2Co17-x Mx ( M＝Ga,Si) COMPOUNDS

The influence of Ga or Si substitution for Co on the structural and magnetic properties of Pr₂Co₁₇ compounds is investigated. All samples studied here are single phase and have the rhombohedral Th₂Zn₁₇-type structure. The unit-cell volume is found to increase linearly by the substitution of Ga for Co,but reduce by the substitution of Si for Co in Pr₂Co₁₇ compounds. In Pr₂Co_17-x M_x, the Curie temperature decreases monoto nically with increasing at an approximate rate of 153K per Ga atom and 175K per Si atom. The saturation magnetic moment of Pr₂Co_17-x M_x ( M=Ga,Si) decreases with increasing x. The rates of the decrease are larger than that expected as a simple dilution. For Pr₂Co_17-xSi_x ,the spin reorientation transition is observed above room temperature. The spin-reorientation temperature Tsrfirst decreases with increasing Si content and then increases at higher x values (x>2). The spin reorientat ion behavior is interpreted by the competition between the Pr and Co sublattice anisotropies. The easy magnetization direction in Pr₂Co_17-xGa_x compounds is perpendicular to the c-axis, and no spin reorientation transition is observed.