Anomalies of thermal expansion and change of entropy of rare-earth diborides at the temperatures of magnetic transitions

An entropy method has been proposed for calculating magnetic heat capacity C-m of rare-earth diborides on their thermal expansion data. It was found that the temperature changes of magnetic entropy Delta S-m(T) calculated from calorimetric data correlate with the magnetic components of lattice parameters Delta a(m)(T) and Delta c(m)(T) calculated from X-ray diffraction data. Using this correlation, a formula for C-m(T) has been derived. Calculations of C-m(7) for TbB2, DyB2, HoB2, and ErB2 have been carried out. The temperature dependencies C-m(T) obtained from X-ray diffraction data are in a good agreement with the calorimetric data. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim