Specific heat below 1 K - Some examples in magnetism

The measurement of specific heal below 1 K by means of a quasi-adiabatic calorimeter, employing adiabatic demagnetization for cooling, is described. The lattice, hyperfine and electronic contributions in the temperature domain 0.05 < T < 4 K are discussed briefly as an introduction to the analysis and exploitation of the magnetic contribution to the specific heat in magnetic insulators. The comparison with simple magnetic models is illustrated by the analysis of the specific heat data of the NdMO3 perovskites, with M = non-magnetic atom. The action of a magnetic field, albeit an internal field, is discussed using NdMO3, M = Fe, Cr and Ni perovskite as examples. Finally, two molecular magnetic ma terials are discussed; Gd-2(ox)[Cu(pba)](3)[Cu(H2O)(5)]. 2H(2)O as a candidate for ferromagnetic order in a rare earth transition metal complex, and Gd(hfac)(3)NITR, with the nitronyl nitroxide magnetic radical interacting with the rare earth.