Takashi Iwashita

Higher Order Spin Coupling in Complex Compounds

From the analyses of the magnetic susceptibility and/or the magnetic heat capacity of the polynuclear complex compounds of iron group ions, it has been suggested that there exists an additional higher order spin coupling besides the usual Heisenberg exchange interaction. It is shown that the higher order spin coupling can be derived from the minimum condition of the free energy of the cluster system. For that purpose, a magnetoelastic term is introduced in the free energy and a dependence of the exchange coupling on the distance between interacting ions is assumed. In an alternative way, it is also shown that the higher order spin coupling can be derived from the perturbation procedure in which the spin-orbit interaction and the usual exchange interaction are taken as the perturbation. A quantitative comparison of the present theory with the values obtained from data analyses makes it clear that the magneto-striction is an important origin for the appearance of the higher order spin coupling.

Effects of the Biquadratic Exchange Interaction in Linear Chain Antiferromagnet

The effects of the biquabratic exchange interaction on the temperature dependence of the magnetic specific heat and sublattice magnetization have been calculated with the use of the spin wave theory for linear chain antiferromagnet. The antiferromagnetic spin structure changes abruptly and begins to make a cant at a certain ratio P c of the biquadratic exchange interaction to the Heisenberg one, which is reasonably small enough to appear in the real antiferromagnet with large spin. This change of the spin structure is shown to give significant effects on the magnetic properties.

Effects of the uniaxial anisotropy on the Curie temperature of the anisotropic Heisenberg ferromagnet with mixed spins S = 12 and S = 1

With the use of the pair model approximation, the effects of the D-term on the Curie temperature of the anisotropic Heisenberg ferromagnet with mixed spins S = 12 have been investigated and shown to be significant for D > 0.

Spin Wave Analysis of the Linear Chain Antiferromagnet CsMnCl3·2H2O

The spin wave dispersion relations of a linear chain antiferromagnet CsMnCl 3 ·2H 2 O have been calculated taking into consideration weak interchain interactions as well as an intrachain interaction and crystalline field potentials. With the use of the dispersion relations, the temperature dependences of the parallel and perpendicular magnetic susceptibilities and the sublattice magnetization have been calculated numerically and compared with the experiments by Kobayashi et al. and Skalyo et al. Satisfactory agreements are obtained with a suitable choice of the exchange constants and the anisotropy parameters which are also consistent with those determined from other analyses.

Two-Dimensional Quadratic Ising Ferromagnet with Apparent Three Spin Interactions

For a spin one-half Ising ferromagnet with two-dimensional quadratic lattice, the effects of the apparent three spin interaction, which is reduced effectively to the bilinear exchange interaction between next nearest neighbors, on the Curie temperature, magnetization and the magnetic specific heat have been calculated with the use of Bethe-Peierls theory. The ferromagnetic order is shown to become unstable when the ratio of the three spin interaction to the bilinear exchange interaction amounts to -1/3. Also it is pointed out that the three spin interaction gives significant changes on the Curie temperature and on the temperature dependences of the magnetization and the magnetic specific heat.

Magnetic Interactions in Quadri-Nuclear Complex Compound [Cr4(OH)6(en)6](N3)6·4H2O

The exchange interactions in the quadri-nuclear complex compound in which the magnetic ions form a cluster of rhomboid structure are studied. In addition to the ordinary exchange interactions, the higher order spin coupling is shown to be necessary to interpret the magnetic susceptibility data.

The Curie temperature of the anisotropic Heisenberg ferromagnet with mixed spins

Abstract The effects of the uniaxial anisotropy and the biquadratic exchange interaction on the Curie temperature of the anisotropic Heisenberg ferromagnets with mixed spins have been investigated. The calculation has been made for the mixed spin systems of ( S =1/2, S =1), ( S =1/2, S =3/2) and ( S =1/2, S =2) withe use of pair model approximation.

Effects of interchain interactions and anisotropy terms on the specific heat of the linear chain antiferromagnet CsMnCl3⋅2H2O

The effects of the interchain interaction and the anisotropy of a crystalline field on the temperature dependence of specific heat in the ordered state of the linear chain antiferromagnet CsMnCl3⋅2H2O are investigated with the use of spin wave theory. It is pointed out that these interaction terms contribute rather important effects to the specific heat and cannot be neglected in explaining the behavior in the low temperature region. Fitting the theoretical specific heat curve with the experimental data has shown that the values of the interaction parameters estimated in the previous analyses of the magnetic susceptibilities and the sublattice magnetization also give satisfactory agreement.

On the Anisotropic Exchange Interaction in [(NH3CH2CH2)2NH2][CUCl4]Cl

The anisotropic exchange constants in diethylenetriammonium chlorocuprate are estimated by the spin wave analyses of the magnetic susceptibility. The anisotropy in the exchange constants is shown to be caused by two terms in the third order perturbation calculation.

Effects of biquadratic-exchange in antiferromagnets

Abstract The effects of the biquadratic-exchange interaction on magnetic specific heat and sublattice magnetization are studied for antiferromagnets. At the critical ratio of the biquadratic-exchange to the Heisenberg interaction, the spin structure changes abruptly and magnetic properties are affected significantly.