Impedance and initial magnetic permeability of gadolinium

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In the present work we report on measurements of the complex impedance and the magnetoimpedance of a textured sample of gadolinium metal. The preferential c -axis orientation of the Gd hexagonal structure is perpendicular to the long axis of the sample. From the experimental data, the complex initial magnetic permeability, mu = mu' + i mu '', was obtained as a function of temperature and frequency of the ac exciting current. We have found that the results for mu'(T) below the spin reorientation temperature may be described as a power law of the reduced temperature t = 1-T/T(SR), where T(SR) is the spin reorientation temperature. This behavior suggests that a genuine phase transition occurs at T(SR). Although the impedance displays a weak anomaly at the Curie temperature, T(C), magnetic measurements indicate that the ferromagnetic response of Gd extends up to this critical point. Thus, two different phases characterizes the cooperative magnetic state of this metal. The frequency dependent results for mu' and mu '' were fitted to a modified Debye formula and the obtained parameters allow us to discriminate between the contributions from domain-wall motion and from magnetization rotation. We obtain that the dynamical properties of the domain walls in Gd are governed by a broad distribution of frequencies whose average value diverge at T(SR). The isothermal magnetoimpedance measurements in temperatures smaller than T(SR) show an interesting plateau at low dc applied fields. This plateau is limited by a characteristic field H(K) whose magnitude decreases rapidly to nearly zero at T(SR), giving further support for the phase transition scenario at this temperature. (C) 2010 American Institute of Physics. [doi:10.1063/1.3288696]1075Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq [04.0938.0