Izuru Kimura

Estimation of the Exchange Constants in CoCl2·6H2O

The values of the exchange constants in NiCl 2 ·6H 2 O are estimated by analyzing the experimental results of paramagnetic susceptibilities by Hamburger and Friedberg. The results are J 1 =(2.4±0.1)k B and J 2 =(0.5±0.2)k B .

On the Specific Heat of Fe(HCOO)2 ·2H2O

A theoretical analysis of the magnetic specific heat of Fe(HCOO) 2 ·2H 2 O is performed on the basis of a two site model, R A =1/2 and S B =2, where R A is the fictitious spin for the lowest doublet. The contribution to the specific heat from A and B sites can be calculated separately and the effect of weak AB interaction is considered by the high-temperature series expansion technique. The experimental result turns out to be well explained by introducing a large S z 4 -term for B site ions. As a microscopic origin of S z 4 -term, the magnetostrictive energy at B site is shown to be favorable.

Molecular Field Theory of Antiferrimagnetism

A theoretical study is made of the magnetic properties of antiferrimagnet using the molecular field approximation. The study is mostly limited to the effects of the presence of two kinds of magnetic ions. It is shown that the effects yield some characteristic behaviors in various magnetic properties of antiferrimagnet: sublattice magnetization, magnetic susceptibility and magnetic specific heat.

The Effect of the Magnon-Phonon Interaction on the Specific Heat of an Antiferromagnet

The effect of the magnon-phonon interaction on the specific heat of an antiferromagnet is calculated on the basis of a simple model. We treat a Hamiltonian which includes terms of quasi-magnons, phonons and magnon-phonon interaction. The Hamiltonian is diagonalized and two branches representing coupled modes are obtained. The specific heat of the coupled system is calculated. It is shown that for weak interaction the contribution from the magnon-phonon interaction is very small, and for strong interaction it in creases rapidly with decreasing temperature and it gives a large correction to the total specific heat at low temperatures.

Calculations of the Specific Heat and the Magnetic Susceptibility of Ferric Ammonium Alum at Very Low Temperatures

The specific heat and the magnetic susceptibility of ferric ammonium alum at very low temperatures are investigated theoretically. The calculated results are in good agreement with the recent specific heat measurement by Vilches and Wheatley with use of appropriate crystalline field parameters for this salt. The results are also compared with the magnetic susceptibility data with a satisfactory agreement.

Solitons in One-Dimensional Antiferromagnet with Uniaxial Symmetry

Dynamical solitons in a one-dimensional antiferromagnet with both a uniaxial anisotropy and an applied magnetic field along the uniaxial axis are investigated theoretically. It is shown that two types of solitons, sine-Gordon kink solitons and pulse solitons are possible. The crossover between both types of solitons is discussed.

On the two-dimensionality of Fe(HCOO)2·2H2O

Abstract With the use of decoration iteration transformation method, the effective coupling J between the successive A-planes of Fe(HCOO) 2 ·2H 2 O is calculated. It is shown that J tends to zero as T → 0 K and the two-dimensionality becomes more remarkable.

On the Paramagnetic Susceptibility of Fe(HCOO)2·2H2O

The powder paramagnetic susceptibility of Fe(HCOO) 2 ·2H 2 O is analyzed on the basis of a two-kind-spin model, i.e. the Ising spin of one-half and the Heisenberg spin of two with the use of the values of parameters, such as the exchange constants and the anisotropy constants, obtained previously. The susceptibility due to the Ising spin is taken into consideration using the high-temperature series expansion result. On the other hand, the susceptibility due to the Heisenberg spin is calculated exactly. The interaction between two kinds of spins is taken into account by using the molecular field approximation. It is shown that the calculated result agrees well with the experimental data and the estimated exchange constants are found to be reasonable compared with those in other formates.

Green Function Analysis of Antiferrimagnetism

The zero-point spin deviations ( Δ R , Δ S ) and the critical temperature ( T N ) of a model antiferrimagnet of vivianite-type spin structure are calculated by the Green function method with the decoupling scheme of Tyablikov. The dependences of the value of Δ R and Δ S on the spin values ( R and S ) are explained by the variation of ferromagnetic effective field which restrains the spin fluctuation caused by antiferromagnetic couplings. The dependence of T N on R and S is not so simple as in the case of antiferromagnets.