Tm Moments Research Articles

Magnetic ordering phenomena in TmS

Neutron diffraction data have been obtained from powder and single crystal specimens of TmS at temperatures ranging from room temperature to 1.7 K and in applied magnetic fields up to 42.8 kOe. In zero field TmS undergoes a transition, at about 8.9 K, to an antiferromagnetic structure which is almost the type two face-centered cubic structure. In this structure there are four G-type or (π,π,π) type antiferromagnetic sublattices such that the moments are parallel in (111) planes, alternating in sign from one such plane to the next. Superimposed on the ordering is a sinusoidal modulation with propagation vectors parallel to [110] directions. The structure is a multidomain one which gives rise to a very complex diffraction pattern. With polarization analysis it was possible to determine the moment directions in the domains. For example, in domains with propagation vector parallel to [11̄0] the moments are parallel to [112̄]. From powder data taken at 1.7 K the maximum value of the Tm moment was estimated to be 4.0 μB. Diffuse streaks of magnetic origin with temperature and field dependence different from that of the satellites were observed which may influence our estimate of the magnitude of the ordered moment. The response of the magnetic reflections to applied magnetic fields can be understood, in part, in terms of domain repopulation.

Polarized-neutron study of TmCo2

Diffraction experiments with polarized neutrons have been carried out on a Tm${\mathrm{Co}}_{2}$ single crystal, at various temperatures, in a field of 57.2 kOe applied parallel to the [$01\overline{1}$] direction. The localized moments on Tm and Co sites have been determined at 4.2 and 100 K from the magnetic densities obtained by Fourier projections. The Tm moment ($5.4{\ensuremath{\mu}}_{B}$ at 4.2 K) is reduced by crystal-field effects. A $3d$-type Co moment is coupled antiparallel to the Tm one. The magnetic scattering amplitudes measured for the reflections to which the $4f$ Tm moment does not contribute give direct evidence for the existence of a diffuse magnetic density. This diffuse density is oscillatory with distance and remains similar at all temperatures. The $4f$ Tm and the $3d$ Co moments have been evaluated at eight temperatures from 4.2 to 250 K. The Co susceptibility above 25 K is temperature independent. The Co behaves as a Pauli paramagnet under the action of two opposite fields: the molecular field due to Tm atoms and the applied field. A collective-electron model is therefore appropriate for the description of paramagnetic susceptibility. At 4.2 K a large increase of the Co susceptibility in the molecular field leads to a value of the Co moment of $0.8{\ensuremath{\mu}}_{B}$. This result can be related to the increase of the susceptibility observed in Y${\mathrm{Co}}_{2}$ in high applied fields and to the first-order ferri-paramagnetic transition of some $R{\mathrm{Co}}_{2}$ compounds, where $R$ stands for rare-earth metals.