Thermal properties of rare earth dodecaborides

We have measured heat capacity and thermal expansion of rare earth dodecaborides REB12 (RE = Y, Tb-Tm, Lu). YB12 and LuB12 are diamagnetics whereas the other dodecaborides are ordered antiferromagnetically. The amplitude of the heat capacity discontinuity at the Neel temperature and the shape of the heat capacity variation in the critical region for all these antiferromagnetics are characteristics for amplitude-modulated magnetic structures. In the ordered state TbB12 reveals two first-order phase transitions, most likely due to magnetic structure changes. The heat capacity of ErB12 just below the Neel point shows an anomaly of unclear origin. From the Schottky contribution to the heat capacity we have determined crystal field parameters. They are completely different than that is estimated from Point Charge Model. (C) 2003 Elsevier Inc. All rights reserved.