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.

We find a mapping of the layered sine-Gordon model to an equivalent gas of topological excitations and determine the long-range interaction potentials of the topological defects. This enables us to make a detailed comparison to the so-called layered vortex gas, which can be obtained from the layered Ginzburg-Landau model. The layered sine-Gordon model has been proposed in the literature as a candidate field-theoretical model for Josephson-coupled high-Tc superconductors, and the implications of our analysis for the applicability of the layered sine-Gordon model to high-Tc superconductors are discussed. We are led to the conjecture that the layered sine-Gordon and the layered vortex gas models belong to different universality classes. The determination of the critical temperature of the layered sine-Gordon model is based on a renormalization-group analysis.

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a b s t r a c t Composition depth profiles of d.c.-plated and pulse-plated Fe-Ni alloys have been investigated with the reverse depth profile analysis method. When d.c. plating is applied, the mole fraction of iron near the substrate is higher than during steady-state deposition since iron is preferentially deposited beside nickel and the achievement of the steady-state deposition condition takes time. The steady-state composition was achieved typically after depositing a 90-nm-thick alloy layer. In the pulse-plating mode, samples with nearly uniform composition could be obtained at a duty cycle of 0.2 or smaller, and a continuous change in the composition profile could be seen as a function of the duty cycle above this value. A constant sample composition was achieved with pulse-plating in a wide peak current density interval. The composition depth profile was also measured for a wide range of Fe 2+ concentration. The different characteristics of the composition depth profile as a function of the deposition mode can be explained mostly in terms of mass transport effects. The elucidation of the results is fully in accord with the kinetic models of anomalous codeposition and with the assumption of the superposition of a stationary and a pulsating diffusion layer. The results achieved help to identify the conditions for the deposition of ultrathin magnetic samples with uniform composition along the growth direction.