Impedance and initial magnetic permeability of gadolinium

Abstract

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 μ=μ'+μ", was obtained as a function of temperature and frequency of the ac exciting current.We have found that the results for μ (T) below the spin reorientation temperature may be described as a power law of the reduced temperature t=1−T/TSR, where TSR is the spin reorientation temperature. This behavior suggests that a genuine phase transition occurs at TSR. Although the impedance displays a weak anomaly at the Curie temperature, TC, 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 μ' and μ" 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 TSR. The isothermal magnetoimpedance measurements in temperatures smaller than TSR show an interesting plateau at low dc applied fields. This plateau is limited by a characteristic field HK whose magnitude decreases rapidly to nearly zero at TSR, giving further support for the phase transition scenario at this temperature.