Specific Heat of Gadolinium and Ytterbium Metals between 0.4 and 4°K

The heat capacities of gadolinium and ytterbium metals are measured between 0.4 and 4 deg K in a He/sup 3/ cryostat. For gadolinium, anomalous humps are observed in C/sub p/ at 1.1, 1.6, and 3.7 deg K. The ground state of the Gd/ sup 3+/ ion is S/sup 8//sub 7/2/ an d consequently, as a result of zero orbital angular momentum of the 4f electrons, the nuclear specific heat is small. The observed C/sub p/ is much larger than expected for the metal alone; the excess entropy could be attributed to magnetic ordering of Gd/sup 3+/ ions in the Gd/sub 2/O/sub 3/ impurity (0.54% of oxygen in our sample). The specific heat of ytterbium, between 0.4 and 4 deg K, can be expressed by C/sub p/(mj/mole deg K) = 1.180T/sup 3/ + 2.90T + 0.012T/sup -2/. The lattice specific heat corresponds to a Debye THETA = 118.1 deg K, which is considerably lower than the value THETA approximates 160 deg K observed for other higher rare earths. The electronic specific heat of ytterbium C /sub E/ = 2.90T is also much smaller than the usual value C /sub E/ approximates 10T. In the nonmagnetic ytterbium metal the 5d electron, normallymore » in the conduction band, is added to the 4f shell which thereby becomes hill. This explains the differences between the specific heat of ytterbium and of the other rare earths. The small term in C proportional to T/ sup -2/, is probably caused by long-range exchange-type coupling between the electronic moments of rare-earth impurities in the ytterbium sample. (auth)« less