G. Wiatrowski

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.

The magnetisation and the correlation functions in thin diluted films (ising model, S=1/2)

The thin diluted ferromagnetic film with SC symmetry is considered in the third-order Matsudaira approximation. The equations for the description of magnetisation and various correlation functions have been derived and the results of the numerical calculations have been presented. In particular the critical temperature, the critical concentration, the magnetisation and various correlation functions are discussed in detail for various film thicknesses and for several magnetic atom concentrations.

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.

Multicompensation effects in multilayers

Abstract Infinite ferrimagnetic AB1AB2-superlattice and A(nA)B(nB)-sandwich structures, with constituents composed of various ferromagnets with equal thickness, are investigated using spin- 1 2 Ising model in a linear cluster approximation. The phase diagrams and layered magnetizations indicate the existence of 0–4-compensation phenomena which are discussed accounting for the role of components thickness and interface couplings.

Some magnetic properties of thin films in a mixed-spin surface Ising model

Abstract A thin ferromagnetic film (S A = 1 2 ) with enhanced surface magnetic moment ( S B = 1) and with surface exchange interactions different from the bulk is investigated by the use of a mixed Ising model. The phase diagrams and the temperature dependences of the magnetizations for several particular cases are presented. We find a new phase in which the transition temperature of any thin film reaches the bulk one when the concentration of higher magnetic moments at the surface is large enough. The magnetization profiles in this region are examined. The surface magnetization phenomenon is qualitatively compared with that observed using in-situ conversion electron Mossbauer spectroscopy on a flat and continuous 21-monolayer Fe(110) film.

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.

Multicompensation effects in an alternating superlattice: linear cluster approximation for spin- Ising model

Abstract An infinite S= 1 2 ferrimagnetic superlattice of atomic planes with various values of exchange interactions and magnetic moments is considered in the framework of an Ising model. The transfer matrix method and linear cluster approximation are applied to derive the expressions for free energy and layered magnetizations, and new types of phase diagrams and magnetization curves for several particular structures are presented. The conditions for the existence of multicompensation points are discussed.