Spin excitations and thermodynamics of the antiferromagnetic Heisenberg model on the layered honeycomb lattice

We present a spin-rotation-invariant Green-function theory for the dynamic spin susceptibility in the spin-1/2 antiferromagnetic Heisenberg model on a stacked honeycomb lattice. Employing a generalized mean-field approximation for arbitrary temperatures, the thermodynamic quantities (two-spin correlation functions, internal energy, magnetic susceptibility, staggered magnetization, Néel temperature, correlation length) and the spin-excitation spectrum are calculated by solving a coupled system of self-consistency equations for the correlation functions. The temperature dependence of the magnetic (uniform static) susceptibility is ascribed to antiferromagnetic short-range order. The Néel temperature is calculated for arbitrary interlayer couplings. Our results are in a good agreement with numerical computations for finite clusters and with available experimental data on the β-Cu₂V₂O₂ compound.     

Theoretical study of the susceptibility of nearly one-dimensional VF2

The paramagnetic susceptibility of a nearly one-dimensional helical magnet VF₂, of the tetragonal body-centered lattice, is calculated on the assumption of classical spins which form linear chains along the c-axis, with strong intra-chain and weak inter-chain exchange coupling. The partition function and the susceptibility are expanded in powers of J′/k_BT, J′ being the inter-chain coupling constant. The coefficients of the expansion are expressible in terms of spin correlation functions for independent linear chains. The susceptibility up to the 3rd power of independent linear chains. The susceptibility up to the 3rd power of J′/k_BT shows, as a function of temperature, a pronounced broad maximum as observed. The specific heat calculated with classical spins fails to reproduce the observation.     

Calculation of short range magnetic order in iron

A spin fluctuation theory for itinerant electrons that includes short-range magnetic order (SRMO) is used to calculate the Curie-temperature (T_c and the temperature dependence of the magnetization and the susceptibility of bulk Fe. When spin correlations are included the Curie-temperature is reduced by 9% to T_c = 2000 K. The calculated temperature-dependence of the magnetization and the magnetic susceptibility are in excellent agreement with experimental results.     

de Haas van Alphen (dHvA) effect in two-dimensional (2D) conductors: susceptibility oscillations

A new scheme for analyzing the de Haas van Alphen (dHvA) effect in nearly two dimensional (2D) metals (i.e. with nearly cylindrical Fermi surface) is presented. The envelope of the magnetic susceptibility oscillations is calculated in the entire range of magnetic fields and temperatures. The resulting envelope function is found to be proportional to a universal function of the dimensionless parameter Q=hω_c/k _B T. The upper (i.e. paramagnetic) branch of the susceptibility envelope has a maximum at a certain Q = 5.45. This universal value may be useful for determining the effective cyclotron mass and the Fermi energy of nearly 2D metals. A simple relation between magnetization oscillations amplitude and calculated susceptibility amplitudes is derived. The corresponding limiting formulae for the magnetization oscillations envelope are found to match smoothly around the value X = 2π²/Q?2 of the Lifshitz-Kosevich (LK) smearing parameter. The influence of Fermi surface sheets with open orbits on magneto-quantum oscillations is considered. Triangle-like rather than saw-tooth-like oscillations at ultralow temperatures are obtained and substantially diminished magnetization and susceptibility amplitudes are calculated. This suggests the possibility of estimating the band structure parameters of Fermi surface sheets from magneto-quantum oscillations measurements.     

The parallel susceptibility at 0 K of the double magnetic helix

The parallel susceptibility x^∥ at 0 K of a double magnetic helix of pitch angle ? in which two species of magnetic ions are acted on by unequal molecular fields is determined. The conditions under which x^∥ is equal to the 0 K perpendicular susceptibility x^⊥ calculated in the past are determined. Comparison is made with the powder susceptibility measurements performed on the orthorhombic compound La₂Fe_1.5Mn_0.5S₅ which displays a double magnetic helix up to T_N = 85 K.     

具有非磁性缺陷的二维自旋玻璃模型

本文提出具有非磁性缺陷(n_m^1/2l<<1)的二维RKKY自旋玻璃模型,分别给出不同温区比热和磁化率的表达式.同时应用渗流理论分析转变温区自旋集团的行为,说明比热膝盖伏峰值和磁化率尖拐状峰值的实验事实. 关键词：     

Ground state correlation in the two-dimensional polarized electron gas

The ground state energy and radial distribution functions of the polarized two-dimensional electron gas with valley degeneracyn _v =1 and 2 are calculated using the hypernetted-chain approximation with the effective correlation factor method for Fermions. The paramagnetic susceptibility is calculated and compared with experiment in silicon inversion layers.     

On the theory of static magnetic susceptibility of NiF2

The magnetic susceptibility of the weak ferromagnet NiF₂ is calculated using self-consistent microscopic calculations. It is shown that a comparatively large longitudinal susceptibility can be due to the rotation of a spin subsystem under the action of a magnetic field. The expression for the piezomagnetic moment of NiF₂ is given.     

Estimation of single-ion anisotropies, crystal-field and exchange interactions in Gd-based frustrated pyrochlore anti-ferromagnets Gd2M2O7 (M=Ti, Sn, Hf, Zr)

The temperature dependence of the experimental results of dc (macroscopic) magnetic susceptibility and nuclear hyperfine properties of frustrated magnetic Gd-based pyrochlore compounds, Gd₂Ti₂O₇, Gd₂Sn₂O₇, Gd₂Hf₂O₇ and Gd₂Zr₂O₇, are analyzed within the frame work of appropriate crystal-field theory and a mean field approximation by introducing effective anisotropic molecular field tensors, and formulating an exact relation between single-ion susceptibility tensors and site susceptibility tensors. Components of the calculated susceptibility along and perpendicular to the local 〈1 1 1〉 axis of the tetrahedral sublattice of pyrochlore structure show that these pyrochlores are easy-planar anisotropic magnetic systems. The crystal-field parameters and anisotropic exchange coupling have been determined and their systematic variations over the Gd-based pyrochlores studied here are discussed.     

Neutron Matter Properties Using Skyrme Interaction

The purpose of the present work is to extend earlier nuclear matter calculations to study the properties of neutron matter. The binding energy per particle, symmetry energy, single particle potential, effective mass, and magnetic susceptibility are calculated using a modified Skyrme interaction. These are calculated as a function of the Fermi momentum k_f in the range 0 < k_f < 2 fm^?1. Two sets of the interaction parameters are obtained by fitting the interaction parameters using the available information on neutron matter. Relativistic corrections to the order 1/c² are also calculated. The relativistic corrections are very small and they increase as k_f is increased.     

Spin state and exchange in the quasi-one-dimensional antiferromagnet KFeS2

We report the optical spectra and single crystal magnetic susceptibility of the one-dimensional antiferromagnet KFeS₂. Measurements have been carried out to ascertain the spin state of Fe³⁺ and the nature of the magnetic interactions in this compound. The optical spectra and magnetic susceptibility could be consistently interpreted using aS=1/2 spin ground state for the Fe³⁺ ion. The features in the optical spectra have been assigned to transitions within thed-electron manifold of the Fe³⁺ ion, and analysed in the strong field limit of the ligand field theory. The high temperature isotropic magnetic susceptibility is typical of a low-dimensional system and exhibits a broad maximum at ∼565K. The susceptibility shows a well defined transition to a three dimensionally ordered antiferromagnetic state atT _N=250 K. The intra and interchain exchange constants,J andJ′, have been evaluated from the experimental susceptibilities using the relationship between these quantities, andχ _max,T _max, andT _N for a spin 1/2 one-dimensional chain. The values areJ=−440.71 K, andJ′=53.94 K. Using these values ofJ andJ′, the susceptibility of a spin 1/2 Heisenberg chain was calculated. A non-interacting spin wave model was used belowT _N. The susceptibility in the paramagnetic region was calculated from the theoretical curves for an infiniteS=1/2 chain. The calculated susceptibility compares well with the experimental data of KFeS₂. Further support for a one-dimensional spin 1/2 model comes from the fact that the calculated perpendicular susceptibility at 0K (2.75×10⁻⁴ emu/mol) evaluated considering the zero point reduction in magnetization from spin wave theory is close to the projected value (2.7×10⁻⁴ emu/mol) obtained from the experimental data.     

Theory of the reciprocal susceptibility of the trigonal boracites and the experiment scheme

Landau theory is used to describe the ferroelectric trigonal phase of Boracites. The temperature dependence of the principal reciprocal susceptibility is obtained. The calculated result shows that at the Curie temperature T_c, the spontaneous polarization jumps. The component of the principal reciprocal susceptibility perpendicular to polarization jumps but the component parallel to polarization does not. A possible experimental scheme for the measurement of the principal reciprocal susceptibility components is presented.     

Characteristics of degenerated four wave mixing in ZnS/CdSe/ZnS quantum dot quantum well with multi-shell structure

The wave functions and eigenenergies of electrons in ZnS/CdSe/ZnS cylindrical quantum dot quantum well (QDQW) have been calculated by solving a three-dimensional nonlinear Schrödinger equation, in the framework of the effective-mass envelope-function theory. The third-order susceptibilities of the degenerated four waves mixing (DFWM) have been calculated theoretically by means of compact density matrix. The third-order susceptibilities as the function of the shell radius R₂, R₃ have been analyzed. The results show that the magnitude of nonlinear susceptibility is increased with the increasing of well radius. The resonance frequency of the photon have a shift when R₂ or R₃ is increasing and the relation between nonlinear susceptibility and relaxation time has also been studied.     

On the theory of localized superconductivity: Fluctuational diamagnetism

The diamagnetic susceptibility of a twinning plane at temperatures slightly higher than the localized superconductivity temperature T_c as well as the heat capacity jump at T = T_c are calculated. The possibility of an appreciable increase of the superconductivity temperature in small particles containing twinning planes is studied.     

The ground state of the neutral Hubbard model

The ground state energy of the neutral Hubbard model is calculated by BCS methods for all values of total spinS _z . Numerical results are given for the simple cubic and for the body centred cubic lattice. Antiferromagnetic ordering and a finite paramagnetic susceptibility is found for all values of the coupling constantV ₀.     

Monte Carlo simulation of magnetic and magnetocaloric properties of binary alloy Gd1−xCx

The Potts-like model is utilized to describe an alloy Gd_1−xC_x with x=0, 0.025, 0.06, 0.09, and the magnetic and magnetocaloric properties are calculated by Monte Carlo method. The effect of the local distortion of the lattice due to adulterated C atom on the exchange interaction between Gd atoms can be considered. The spontaneous magnetization, specific heat, and magnetic susceptibility are calculated. It is found that the magnetization at low temperature decreases but phase transition temperature from ferromagnetic to paramagnetic increases, as the concentration of the C atom in the system increases. Moreover, the specific heat and the susceptibility exhibit peaks at the transition temperature. For two external magnetic field h/J=0.25 and 10.0, the magnitude of the isothermal magnetic entropy change in binary alloy is more than in pure Gd system. Furthermore, the range of temperature of half peak in the curve of the magnetic entropy change becomes wide and the refrigerant capacity increases in the alloy.     

交换作用对CeF3晶体磁性和磁光效应的影响

研究了顺磁性晶体CeF₃内交换作用有效场随温度的变化关系，给出了其形式为H_in=(-0.68-0.002T)×10^-6M.结合该关系，用量子理论的计算得到了与实验值吻合较好的磁化率倒数、Verdet常数倒数随温度的变化关系，并且用光磁效应的概念和规律对结果作了进一步分析，指出光诱导促进了该晶体内电子间的交换作用. 关键词： 3晶体')" href="#">CeF₃晶体 交换作用 磁光效应 光磁效应     

Effects of spin fluctuations on the paramagnetic susceptibility and metamagnetic transition in UPt3

The paramagnetic susceptibility for UPt₃ is calculated in the static gaussian statistics of spin fluctuations by using a realistic itinerant electron model. The magnetic field dependence of the magnetisation is also calculated and it is shown that the metamagnetic transition occurs at about 140 T.     

Controlling the speed of electromagnetic waves in TbMnO3 in the sinusoidal antiferromagnetic phase by means of an external magnetic field

The possibility of controlling the speed of electromagnetic waves in TbMnO₃ of sinusoidal electromagnetic structure is investigated. Expressions for the components of the susceptibility tensors are obtained. Frequency dependences of the speed of electromagnetic waves are calculated for different values of an external magnetic field.     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.