Low-temperature properties of layered Heisenberg ferromagnets

Abstract

Spin-wave theory is used to study the effects of interlayer coupling on the properties of layered Heisenberg ferromagnets with S=-. The asymptotic expressions of magnetization and specific heat with temperature and interlayer coupling strength (J, ) are given in two low-temperature regimes distinguished by a characteristic temperature To =2J] /k&. It is shown that the interlayer coupling, though very small, is essential if long-range order at nonzero temperature is to exist.

Theoretical investigations of the local distortion and electron paramagnetic resonance parameter for CdCl 2 :V 2+ and CsMg X 3 :V 2+ ( X = Cl, Br) systems

“…Of course, in order to detailedly clarify the local distortion, more careful experiments especially electron nuclear double resonance (ENDOR) are required. It is remarked that according to the high order perturbation formula, D is directly linearly related to ζ [7] and directly proportional to the square of ζ ′ , [7] respectively. But, our results show that the function of D vs. ζ is not a strictly linear relation, as well as D vs. ζ ′ is not a strictly quadratic relation.…”

“…Vicaro et al [5] gave a theory of the EPR parameter for d 4 /d 6 TM clus-ters with tetragonal symmetry and interpreted the EPR parameter of Cr 2+ in GaAs. Du et al [6,7] investigated the EPR parameters for RX:V 2+ (R=Na, K, Rb; X=Cl, Br, I), Al 2 O 3 :Cr 3+ and CsMgX 3 :Cr 3+ (X=Br, I) systems, etc., and established the formulae of EPR parameters for d 3 configuration ions in the trigonal ligand field. Furthermore, the local distortion parameters and EPR parameters are also analysed by Zheng and Wu et al [8−11] based on these formulae for CdCl 2 :V 2+ and CsMgX 3 :V 2+ (X=Cl, Br, I) systems.…”

“…coupling parameter model, the complete energy matrix (120×120) for d 3 ). In the linear combination of atomic orbitals (LCAO) method, the molecular-orbital basis can be written as [7]…”

“…coupling coefficients ζ and ζ ′ , which are correlated with the s.o. coupling coefficients of central metal ion (ζ 0 d ) and its ligand (ζ 0 p ), can be expressed as [7] ζ = N t…”

Investigations of the electron paramagnetic resonance parameters and the tetragonal local structure for (VCl 6 ) 4− coordination complex in MCl:V 2+ (M = Na, K, Rb) systems

“…However, so far, there has been no satisfactory and quantitative unified explanation for the EPR and optical spectra, and the local structure of V 2+ ions in MCl (M=K, Na, Rb) crystals. For instance, Du [10] has carried out a theoretical calculation of the g factor in MCl:V 2+ systems based on the cluster approximation. According to the two spin-orbit coupling parameter model and high-order perturbation formulas.…”