Magnetic properties and magnetic structures of TmSe at low temperatures

Abstract

The low temperature magnetic properties and structures of a polycrystalline sample of TmSe (a = 5.683 A) have been studied by various experimental techniques. Magnetic susceptibility measurements indicate a Curie-Weiss behaviour at high temperatures with an effective moment of 6.88 µB, which corresponds to a valence state of 2.8+. An anomaly in the susceptibility behaviour is also observed at T ~ 40 K. Magnetization measurements at 2 K and 4.2 K, respectively, give no indication of reaching saturation in a field up to 380 kOe and give a maximum moment of 3.8 µB per Tm ion. Neutron diffraction measurements show the existence of two magnetic transitions at TN1 ≈ 40 K and TN2 ≈ 3.5 K. Analysis of the neutron diffraction spectra indicates that the magnetic ordering is not long-range and can be explained as a short-range order at T ~ 40 K and by assuming the existence of magnetic microdomains below 3.5 K. The magnetic moment per Tm ion at 2 K is equal to 2.32 µB. Time-of-flight (TOF) inelastic neutron scattering measurements show no evidence of crystalfield splitting and a Lorentzian quasi-elastic peak with a width Ɖ(HWHM) which follows a temperature dependence given by Ɖ(T) = 0.337 T0.62. Mossbauer effect measurements show the appearance of some kind of magnetic order at T ~ 40 K in agreement with susceptibility and neutron diffraction measurements. We do not yet have a clear understanding of the magnetic behaviour of our TmSe sample. However, we believe that the abnormal behaviour of our sample is due to deviation from exact stoichiometry and the presence of vacancies caused by a Tm deficiency.