Specific Heat of Samarium Metal between 0.4 and 4°K

Abstract

In addition to the usual lattice and electronic terms, proportional to $T^3$ and $T$, respectively, the specific heat of most rare earth metals at low temperatures has two other contributions: a magnetic specific heat due to exchange interaction between the electronic spins, and a nuclear specific heat due to splitting of the nuclear energy levels in the strong magnetic field produced by the $4f$ electrons. Samarium metal is antiferromagnetic below 13.6°K and the magnetic specific heat, according to the spin wave theory, should be proportional to $T^3$. The nuclear specific heat has a $T^{-2\mathrm{}}$ temperature dependence in the first approximation; the next term in a series expansion proportional to $T^{-4\mathrm{}}$ was also included in the analysis. We may thus write $C_p=A{T}^3+BT+D{T}^{-2\mathrm{}}-E{T}^{-4\mathrm{}}$, where the first term represents both the lattice and magnetic specific heats. Values of the constants, as determined by the method of least squares from 71 experimental points between 0.4 and 2.5°K, are (for specific heat in millijoules/mole°K): $A=0.88-1.11\mathrm{}$; $B=12.1\mathrm{}$; $D=8.56\mathrm{}$; $E=0.021\mathrm{}$. The magnetic specific heat appears to depend on the time the sample spent in the vicinity of the antiferromagnetic Curie point when it was cooled down, hence the variations in the value of $A$. Constants $B$ and $D$ are probably accurate to 5% and 2%, respectively. The effective magnetic field at the nucleus, as calculated from the value of constant $D$, is 3.3×${10}^6$ gauss.