Magnetic-ion-lattice interaction: Rare-earth antimonides

Abstract

We have investigated the magnetic, elastic, and thermal properties of the LnSb series. For the compounds which do not undergo a structural or magnetic phase transition (PrSb and TmSb), we measured Schottky specific-heat anomalies, Van Vleck susceptibilities, and anomalies in the elastic constants. All these properties can be interpreted quantitatively as effects due to the crystal-field split levels of the ground-state J multiplet. For the compounds which undergo magnetic phase transitions (SmSb and GdSb), we find in the case of SmSb similar effects in the paramagnetic region as for PrSb and TmSb, followed by sharp specific-heat and thermal-expansion anomalies at $T_N=2.11\mathrm{}$ °K. In GdSb we find elastic anomalies for $T<\mathrm{}{T}_N=24.4\mathrm{}$ °K due to domain-wall stress effects which can be partly removed by application of a magnetic field. DySb, HoSb, and ErSb undergo magnetic and structural transitions at $T_N=9.5, 5.25, \mathrm{and} 3.53$ °K, respectively. We observe softening of the $c_{11}-c_{12}$ mode for DySb and HoSb, which can be interpreted quantitatively. In ErSb no elastic mode softens for $T>\mathrm{}{T}_N$, indicating that the structural transition involves a coupling of the magnetic ion to other modes than the macroscopic strain. Large thermal-expansion anomalies are observed, especially for ErSb with $H\sim 6$ kOe, with strong domain-wall stress effects for the elastic modes for $H\le 6$ kOe and $T<\mathrm{}{T}_N$. A magnetic field cannot separate the structural and magnetic transition temperatures ($T_a=T_N$) but can only cause both to shift to lower temperatures. The magnetoelastic coupling constants, determined from the temperature dependence of the elastic constants, can be interpreted for the LnSb series as being due to the strain modulation of the crystal field.