Relaxation measurements on ferromagnetic rare earth hydroxides

Abstract

The hydroxides (RE(OH)3) of the rare earths Tb, Dy, and Ho are known to be ferromagnetic at liquid He temperatures. They show an extreme magnetic anisotropy. Measurements of their ac susceptibility in their real and imaginary parts from 1.5 to 700 Hz are reported. The low‐field measurements reveal Cole‐Cole semicircles with well defined relaxation times, leading to activation energies of a few 10−3 eV. The high‐field ac susceptibility shows an abrupt jump at a well defined amplitude of the driving field. As demonstrated by switching experiments it takes tens of minutes for the magnetization to follow a change of the dc magnetic field. The time variation of the magnetization can be approximated by a logarithmic law. It can be concluded from a phenomenological description that two different relaxation processes are observed the first of which is thermally activated and the second one is similar to a thermal after‐effect.

Relaxation in the ferromagnetic phase of terbium arsenate (TbAsO4)

“…Q = 6.6 K is the activation energy of a thermally activated relaxation process. A similar process was found by Schlachetzki and Eclrert [28] in the RE(OH),. However, these authors believed the second relaxation step to be due to domain wall motion and they explained the first step by a thermal after-effect with frequency-independent absorption.…”

“…Relaxation effects similar to those in TbAsO, were observed in dysprosium ethylsulfate, DYES, [19] and in the hydroxides of the rare earths [28]. The authors interpreted their results by assuming two well-isolated relaxation steps.…”

Dilution-Induced Slow Magnetic Relaxation and Anomalous Hysteresis in Trigonal Prismatic Dysprosium(III) and Uranium(III) Complexes

“…Only the faster relaxation at high frequencies in 3 , which becomes dominant upon dilution of the spins, may be ascribed to a molecular process. Analogies for this slower process can be drawn from paramagnetic relaxation studies performed on the compounds Ln(OH) 3 (Ln = Tb, Dy, Ho), dysprosium ethyl sulfate (Dy(CH 3 CH 2 SO 4 ) 3 ·9H 2 O, DyEtS), and terbium arsonate starting in the 1960s. In these systems, two relaxation domains are also apparent at low temperatures, albeit on a much faster time scale.…”

Field dependence of the hyperfine splitting of holmium in holmium hydroxide

“…Conversely, static and dynamic magnetisation measurements provide useful tests of the parameters derived from optical spectroscopy. The hydroxides have in fact been extensively studied by magnetisation, susceptibility, and paramagnetic resonance measurements (Wolf et a1 1968, Scott et al 1969, Scott 1970, Schlachetzki and Eckert 1972, Skjeltorp et a1 1973, Catanese et a1 1973. Measurements of hyperfine splittings can provide particularly delicate tests of theoretical models but the only such measurements so far reported on the hydroxides are a zero-field Mossbauer study of antiferromagnetic Gd(OH), (Katila et al 1972), a zero-field NMR study of ferromagnetic Ho(OH), (Bunbury et a1 1985, to be referred to as I) and a brief report of the field dependence of the hyperfine splitting of 0953-8984/89/071309 + 19 $02.50 0 1989 IOP Publishing Ltd Table 1.…”