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, = Ј+ i Љ, was obtained as a function of temperature and frequency of the ac exciting current. We have found that the results for Ј͑T͒ 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 Ј and Љ 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.

Magnetoresistance of polycrystalline gadolinium with varying grain size

“…T SR . 4 This is similar to the value of H max observed by us. Above T SR for Bulk Gd, E A has a finite value with a maximum at T C (Ref.…”

“…Existence of such a phase transition like behaviour has been suggested from recent magnetoimpedance measurement in strongly textured samples. 4 In Film-A, with intermediate grain size, these features at T SR and T * which have seen in the Bulk sample also persist to some extent, although much suppressed and appear at lower temperatures. The jDq k j in low field shows the broad maxima at 210 K and a shallow minima at$165 K. On cooling to lower T, jDq k j increases again.…”

“…[1][2][3][4][5][6]15 The resurgence in the investigations on magnetic properties of Gd arises from the possibility of utilizing the rather high magnetic moment (and high saturation magnetization) in multilayer thin film applications 7 and also understanding basic physics in a metal with localized moments. Some of the recent magnetic studies focus on nanostructured samples with grain size in the domain of few tens of nm.…”

Enhanced spin pumping near a magnetic ordering transition

“…This magnetic susceptibility diverges as T is lowered toward the Curie temperature at a standard second-order paramagnetic to ferromagnetic phase transition, as expected for Gd (at least from DC measurements) 62,63 . Thus, Eq.…”

Effect of varying dimensions on gadolinium rectangular thin film elements: micromagnetic simulations

“…[9] This gives an approximate exchange stiffness constant A = 5.62 × 10 −12 Jm −1 . A saturation magnetization value of M S = 2.077 × 10 6 Am −1 [9] and a uniaxial magnetocrystalline anisotropy K u = 1.7 × 10 5 Jm −3 [21] acting preferentially along the c-axis [21,22,23] were used. A damping parameter of α = 0.5 was used; this is a relatively large value which allows the system to converge to an energy equilibrium in a more reasonable time [11] and is an appropriate value for an investigation that is not focussed on dynamics.…”