J. Mielnicki

The ising-heisenberg two-atom cluster approximation of a ferromagnet (S = 12)

Abstract In the paper the two-atom cluster model with two Heisenberg spins in the Ising surrounding has been proposed for the description of the Heisenberg ferromagnet. In the frame of this model the general set of two equations has been derived, hence the J/kT c value, the magnetization curve, the correlation function between n.n. spins, the magnetic contribution to specific heat and magnetic susceptibility have been calculated for the particular case of a ferromagnet with sc symmetry.

The magnetization of thin ferromagnetic film in Ising approximation (S = 12)☆

Abstract In the paper thin ferromagnetic films with perfect crystal structure and with structure of diluted alloy have been considered. For both cases the magnetization profiles across the film for various temperatures and various film thicknesses, together with the corresponding critical temperatures have been calculated. For the case of film with diluted alloy structure the relation of critical concentration of magnetic atoms on film thickness has been also found.

A simple method of basic properties description of diluted ferromagnetic alloys (Ising model, S = 12

Abstract A simple method of basic magnetic properties description of diluted ferromagnetic alloys with S = 1 2 is discussed for the case of Ising approximation. As a result the relations for magnetization curve, internal energy, magnetic contribution to specific heat and magnetic susceptibility have been obtained for arbitrary concentration c of magnetic atoms. As an illustration the corresponding curves, calculated for several values of c , have been also presented.

A discussion of some magnetic properties of the square, Ising lattice with a fluctuating exchange integral

The magnetisation curve and the critical temperature of the square Ising lattice with a fluctuating exchange integral has been investigated using the Matsudaira method. Particular attention has been drawn to the reentrant ferromagnetism phenomenon and it has been shown that it strongly depends on the accuracy of calculations with a tendency to disappear when the accuracy is improved.

A simple method of magnetization curve calculations in the Heisenberg model (S = 12)

Abstract A simple method of magnitization calculations has been proposed and applied for the Heisenberg model of a ferromagnet with S = 1 2 . The general equation for magnetization in this model has been obtained, which with additional approximations reduces to Tyablikov, Ising or MFA results. On the basis of the derived equation the magnetization curve for the sc lattice has been obtained and compared with the results of other theories.

Some magnetic properties of the diluted square ising lattice with fluctuating exchange integrals (S = 12)☆

Abstract The site- and bond-disordered ferromagnet is examined with the use of the 1st and 3rd Matsudaira approximations. As a result, the phase diagrams, the magnetization curves and the correlation functions between nearest neighbour spins for various c and Δ parameters, characterizing the dilution and the fluctuations of the exchange integral, are discussed in detail.

The magnetization curve calculations of the Ising ferromagnet with S = 1

Abstract In the paper the general method of magnetization calculations for the Ising ferromagnet with arbitrary spin value has been developed. Detailed calculations have been made for the particular case of S = 1 and for the sc lattice, hence the critical temperature and the magnetization curve together with the 〈( S z ) 2 〉 vs. temperature relation have been obtained.

Magnetization curve calculations of diluted alloys in the approximated Heisenberg model

Abstract A simple method for describing the basic magnetic properties of diluted ferromagnetic alloy with S = 1 2 is discussed for the case of a Heisenberg approximation for a simple cubic lattice. As a result, the relations for the magnetization curve and Curie temperature are obtained for arbitrary concentration c of magnetic atoms. As an illustration, the corresponding curves, calculated for several values of c , are also presented.

The anomalous behaviour of the specific heat of the dilute ising ferromagnet at the critical concentration region

Abstract The magnetic contribution to the specific heat in the diluted two-dimensional and bulk ferromagnets is considered in the frame of the one-atom cluster approximation (1-ACA) of the Ising model. As a result the anomalous behaviour of the specific heat at the critical concentration region is predicted. This anomaly is probably due to the small magnetic clusters which play an important role at magnetic atom concentrations below or just above the critical concentration co.

The magnetization and the spin-correlation functions in a thin ferromagnetic film (Ising model, S=case12)

Abstract In the paper the method of calculation of thin-film magnetization and two-spin correlation functions is developed. The numerical results for film with sc symmetry and composed to two atomic layers are presented. As it has been shown the correlation functions depend not only on the distance between the spin-pair in the sample.