Magnetoelastic properties of RE-3d intermetallics

The authors present magnetisation measurements performed on a single crystal of TbCo2 as well as spontaneous distortion studied by X-ray powder diffraction. At any temperature below Tc (240K) the easy magnetisation direction is (111) while the most difficult is (100). A huge rhombohedral distortion appears below Tc; at 4.2K the angular variation between the cube edges is epsilon =4.4*10-3 rad. The anisotropy due to cobalt being negligible, the authors have analyzed the results in terms of the three contributions acting on the 7F6 ground state multiplet of the Tb3+ ions: crystal field, exchange field and magnetoelastic energy. At 4.2K, as the anisotropy of Tb is very high, a 135 kOe field applied along the (100) or the (110) is not strong enough to align the magnetisation parallel to these axes. As in TbFe2, the large spontaneous rhombohedral distortion results from a strong molecular field associated with strong crystal field effects. The molecular field leads to almost the fundamental level Jz=6 ( mu Tb approximately=9 mu B) that is a very anisotropic 4f distribution and the crystalline field essentially arises, as generally observed, from the d character of the conduction band.

https://iopscience.iop.org/article/10.1088/0305-4608/9/5/005/pdf

Magnetic properties and spontaneous distortion in TbCo2

The low Curie temperature $({T}_{C}\ensuremath{\approx}28\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and small ordered moment $({M}_{0}\ensuremath{\approx}0.17\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}\phantom{\rule{0.3em}{0ex}}{\mathrm{f.u.}}^{\ensuremath{-}1})$ of $\mathrm{Zr}{\mathrm{Zn}}_{2}$ make it one of the few examples of a weak itinerant ferromagnet. We report the results of susceptibility, magnetization, resistivity, and specific heat measurements made on high-quality single crystals of $\mathrm{Zr}{\mathrm{Zn}}_{2}$. From magnetization scaling in the vicinity of ${T}_{C}$ $(0.001l\ensuremath{\mid}T\ensuremath{-}{T}_{C}\ensuremath{\mid}∕{T}_{C}l0.08)$, we obtain the critical exponents $\ensuremath{\beta}=0.52\ifmmode\pm\else\textpm\fi{}0.05$ and $\ensuremath{\delta}=3.20\ifmmode\pm\else\textpm\fi{}0.08$, and ${T}_{C}=27.50\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Low-temperature magnetization measurements show that the easy axis is [111]. Resistivity measurements reveal an anomaly at ${T}_{C}$ and a non-Fermi liquid temperature dependence $\ensuremath{\rho}(T)={\ensuremath{\rho}}_{0}+A{T}^{n}$, where $n=1.67\ifmmode\pm\else\textpm\fi{}0.02$, for $1lTl14\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The specific heat measurements show a mean-field-like anomaly at ${T}_{C}$. We compare our results to various theoretical models.

Ferromagnetic properties of Zr Zn 2

The anisotropic magnetostriction of the cubic Laves-phase compounds RCo2 (R = Pr, Nd, Gd, Tb, Dy, Ho, and Er) has been measured from 4.2 K to above the ordering temperatures. Large magnetostrictions are observed for all compounds except GdCo2 the largest effect being in TbCo2. An attempt is made to deduce the single crystal magnetostriction constants from the measured data and it is concluded that no simple model will account for them. Large volume strains are observed notably in PrCo2 and ErCo2 which are tentatively attributed to a large volume-dependence of the anisotropy.

Magnetoelastic properties of (Rare-Earth)–Co2 compounds. II. The anisotropic magnetostriction

Publisher Summary This chapter discusses the magnetic properties of intermetallic compounds involving rare earth metals. Three different concepts are discussed—namely, magnetism, intermetallic compounds, and rare earth metals. The chapter describes the basic concepts and the central ideas that are connected with the magnetic properties of RnBm intermetallic compounds of rare earth metals R with other metals B. The chapter is concerned with intermetallic compounds where the second component has a moment that is distinctly non-zero. Typical compounds are for instance iron or cobalt compounds. It is concerned with boundary cases that do not fit into the two preceding sections. A typical boundary case will be for instance a system based on YCo 2 , in which a 3D moment appears when a third component is substituted. It also covers some striking phenomena that can be summarized by the term “time dependence.” Some specific hard magnetic materials that are of great technical significance are discussed. The leading compound is SmCo 5 and a general discussion of the significance of this compound with respect to technical applications is presented in the chapter.

Chapter 14 Magnetic properties of intermetallic compounds of rare earth metals

Magnetostriction measurements have been carried out in the cubic Laves phase compounds DyCo2, HoCo2 and ErCo2 from 10K to well above their respective Neel temperatures TN. The observed magnetostrictions are very large ( approximately 10-3). The measurements confirm the extremely high anisotropy of these materials. The expected values of the saturation magnetostriction at 0K are similar in sign and magnitude to those found in the corresponding rare earth metals. This fact and the scaling of magnetostriction with rare earth sublattice magnetization indicates that the rare earth ion is the main source of the magnetostriction. The metamagnetic transition above TN has been studied, the relation between critical field and temperature being nonlinear for HoCo2 and ErCo2. The compounds are highly anisotropic above TN and all the features indicate that the field-induced phases are likely to be ferrimagnetic.

https://iopscience.iop.org/article/10.1088/0305-4608/5/9/016/pdf

Magnetostriction of some cubic rare earth-Co2 compounds in high magnetic fields

Measurements of the specific magnetisation, sigma , of high-purity samples of the weak ferromagnetic ZrZn2 in the temperature range 2.5-270K and in pulsed magnetic fields of up to 17 T are presented. The data indicate that ferromagnetism is an intrinsic property of ZrZn2 and are consistent, below the ordering temperature with the Stoner-Wohlfarth model of very weak itinerant ferromagnetism. The Curie temperature, Tc, is higher than that previously measured with the same samples (27K compared with 21K). It is estimated that Tc increases significantly with thermal expansion in the paramagnetic region but is accompanied by a decrease in the 0K susceptibility chi 0; thus the prediction of the Stoner-Wohlfarth model of a linear dependence of chi -1 on T2 is retained. The observed Curie-Weiss temperature dependence in conjunction with the parallel nature of the sigma 2 against H/ sigma isotherms is thus inconsistent with this model.

https://iopscience.iop.org/article/10.1088/0305-4608/8/6/027/pdf

D Melville

Papers

Magnetostriction of some cubic rare earth-Co2 compounds in high magnetic fields

The magnetic properties of high-purity ZrZn2 in pulsed fields of up to 17 T