S. Mészáros

Magnetic particle hyperthermia: Néel relaxation in magnetic nanoparticles under circularly polarized field.

The mechanism of magnetization reversal in single-domain ferromagnetic particles is of interest in many applications, in most of which losses must be minimized. In cancer therapy by hyperthermia the opposite requirement prevails: the specific loss power should be maximized. Of the mechanisms of dissipation, here we study the effect of Néel relaxation on magnetic nanoparticles unable to move or rotate and compare the losses in linearly and circularly polarized fields. We present exact analytical solutions of the Landau-Lifshitz equation as derived from the Gilbert equation and use the calculated time-dependent magnetizations to find the energy loss per cycle. In frequencies lower than the Larmor frequency, linear polarization is found to be the better source of heat power, at high frequencies (beyond the Larmor frequency) circular polarization is preferable.

Transverse and secondary voltages in Bi2Sr2CaCu2O8 single crystals

Abstract Multicontact configuration is one of the most powerful arrangements for electrical transport measurements applied to study vortex phase transition and vortex phase dimensionality in strongly anisotropic high- T c superconducting materials. In this paper we present electrical transport measurements using a multiterminal configuration, which prove both the existence of guided vortex motion in Bi 2 Sr 2 CaCu 2 O 8 single crystals near the transition temperature and that secondary voltage in zero external magnetic field is induced by thermally activated vortex loop unbinding. The phase transition between the bound and unbound states of the vortex loops was found to be below the temperature where the phase coherence of the superconducting order parameter extends over the whole volume of the sample. We show experimentally that 3D/2D phase transition in vortex dimensionality is a length-scale-dependent layer decoupling process and takes place simultaneously with the 3D/2D phase transition in superconductivity at the same temperature.

Length-scale-dependent phase transition in Bi2Sr2CaCu2O8 single crystals

Electrical transport measurements using a multi-terminal configuration are presented, which prove that in Bi2Sr2CaCu2O8 single crystals near the transition temperature in zero external magnetic field the secondary voltage is induced by thermally activated vortex loop unbinding. The phase transition between the bound and unbound states of the vortex loops was found to be below the temperature where the phase coherence of the superconducting order parameter extends over the whole volume of the sample. We show experimentally that 3D–2D phase transition in vortex dimensionality is a length-scale-dependent layer decoupling process and takes place simultaneously with the 3D–2D phase transition in superconductivity at the same temperature.

The Role of Iron in the Enhancement of Negative Magnetoresistance in La0.8Sr0.2FexCo1−xO3−z

The role of iron in enhancing the magnetoresistance in the compounds La0.8Sr0.2FexCo1−xO3−z was investigated by studying the electronic and magnetic structure of La0.8Sr0.2FexCo1−xO3−z as a function of temperature. For this purpose 57Fe transmission Mossbauer spectroscopy, magnetoresistance, as well as AC and DC magnetization measurements were applied. The detailed study of the temperature dependence of 57Fe Mossbauer parameters gave possibility to explore correlations between the local electronic and magnetic state of iron and the magnetic susceptibility as well as magnetoresistance in La0.8Sr0.2FexCo1−xO3−z. On the basis of the obtained results an attempt was made to explain the exotic magnetic and MR properties of these perovskites.

Disordered magnetic phase in partially oxidized bulk nanocrystalline iron

Magnetically frozen partially disordered state was observed in nanocrystalline bulk iron prepared by ball-milling of microcrystalline Fe. Role of nanostructure and oxidized fraction is pointed out. Altough we have found a small constituent which is proportional to 1/T in the ZFC curve, the magnetization scaling with T3/2 at high fields and the hysteretic behavior in FC-ZFC curves signalizes the presence of frozen ferromagnet at low temperatures.