L. Wojtczak

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 role of interface anisotropy in spin wave resonance spectra of magnetic multilayers exchange coupled through nonmagnetic f.c.c. spacer

In the paper, the influence of interface anisotropy on the spin wave resonance (SWR) characteristics has been investigated and the accuracy of sample preparation necessary to compare the experimentally obtained SWR spectra of magnetic multilayers with theoretical predictions has been estimated. The transfer matrix approach has been applied to the calculation of the energy and relative intensities of SWR spectra as a function of the spacer thickness. The oscillatory exchange coupling between two ferromagnetic layers through nonmagnetic f.c.c. spacer has been employed to investigate spin wave profiles. Various pinning conditions at the external surfaces have been considered and the role of interface anisotropy have been discussed in detail. The results obtained show that for very thin spacers, the difference of one monoatomic layer of the spacer thickness can significantly influence the character of the spectra obtained. It has been also found, for the wide range of interface anisotropy parameters, that for thicker spacers (d≥10 monoatomic layers), where the interlayer exchange coupling is rather weak, the interface anisotropy is the main factor determining the parameters of SWR spectra.

Biomedical applications of small silver clusters

The ground-state properties of small silver clusters Agn (2⩽n⩽24) have been studied using a linear combination of atomic Gaussian-type orbitals within the density functional theory. The results show that the Ag13 clusters, due to their noticeable magnetic moment and their considerable highest occupied-lowest unoccupied molecular orbital gap, are promising candidates for the magnetic applications of nanoparticles. In particular, our study suggests that the silver nanoclusters made out of Ag13 clusters, as building blocks, are suitable for possible future applications in biomedicine, since they could improve some present-day difficulties of magnetic nanoparticles such as toxicity and opsonization.

Magnetic-dependent structure in eight-atom gold clusters

We have performed ab initio calculations on the lowest energy structure of eight-atom gold clusters, a tetracapped square with D4h symmetry, locking it to several total magnetic moments. We have found that for nonzero values of the total magnetic moment, the D4h symmetry is not stable. We have also found that for a fixed nonzero total magnetic moment, the stable structure is a distortion of the tetracapped square, along the square’s diagonals. This structure has a D2h symmetry. The rest of possible structures for this cluster have been calculated as well, and no magnetism-dependent deformation was found, except for the tetracapped tetrahedron with symmetry Td, which is unstable for nonzero total magnetic moment. In this case, the favored structure is a bicapped octahedron with symmetry D2d. The structural change due to magnetic constraints is relevant since the surface of gold clusters has shown a catalytic behavior highly dependent on the structure.

Lattice vibrations in thin films

Abstract The Greens function method is applied to the investigation of the energy spectrum of phonons in thin films taking into account an anharmonic model. The Debye model for thin films is studied. A mean square displacement of atoms is calculated, properties of the melting point of thin films are shown from Lindemanns law of the melting temperature. The Debye-Waller factor is discussed.

Magnetic properties of bilayers with a mixed-spin interface

Abstract A thin ferromagnetic bilayer structure with interface magnetic moment and different exchange interactions is studied in terms of a mixed Ising model. The phase diagrams of critical temperature T C vs. interface parameters and the temperature dependence of layered magnetizations are presented. In particular, the magnetization profiles across bilayer show us the existence of the interface magnetism phase and temperature reversal of magnetization profiles assigned to special domains of phase diagrams provided the interface perpendicular anisotropy is large enough. The results form the basis to extend our recent studies on the Hood–Falicov approach to the giant magneto-resistance description.

SURFACE MELTING DESCRIPTION

Abstract The surface melting is regarded in terms of the order parameter profiles which characterise phases extended inside a whole sample. The characterisation of the phase is, however, due to the order parameter behavior at the surface. The phase really observed is predicted by means of the thermodynamic conditions; thus, the surface melting phase is in competition to the softening modes at the surface. The presented idea is based on the discussion concerning the possible results of the leading theories, a modified van der Waals approach and an Ising type model for pseudospins. The experimental evidence is reviewed and interpreted.

Surface melting of aluminum

The Landau-type theory of inhomogeneous systems is applied to study the surface melting of aluminum. In order to describe the bulk properties, the potentials obtained ab initio for aluminum by Straub et al. are introduced. Conditions for appearance of surface melting and surface non-melting are formulated. It is found that the calculated surface melting temperature depends on parameters of the theory and is always lower than that obtained experimentally for Al(110) face. The temperature dependence of the quasi-liquid layer thickness exhibits logarithmic behavior in accordance with the experiments. The parameters of the theory can be correlated with experimentally verified quantities.

Ferromagnetic nanostructures in the generalized Valenta model

Ferromagnetic nanostructures are an area of great interest for modern physics. A comparison of experimental data and theoretical results shows that the use of the standard molecular field approximation is insufficient for the description of the nanostructure properties. Therefore in the present paper we use the reaction field approach in order to test the Valenta model generalized in this way. The agreement between experiment and theory is then excellent.

Surface phase transitions

Within Lipowskys model we consider the surface phase with a specific shape of the order parameter appearing above the bulk phase transition point at the surface. We apply the results to a description of the surface magnetization whose behavior was experimentally observed as the magnetization in a semi-elliptical form.