Influence of magnetic impurities on the heat capacity of nuclear spins

It is found that in a wide range of temperatures and magnetic fields even a small concentration of magnetic impurities in a sample leads to a $T^{-1}$ temperature dependence of the nuclear heat capacity. This effect is related to a nuclear-spin polarization by the magnetic impurities. The parameter that controls the theory turns out not to be the impurity concentration $C_{imp}$ but instead the quantity $c_{imp} \mu_e / \mu_n$, where $\mu_e$ and $\mu_n$ are the magnetic moments of an electron and a nucleus, respectively. The ratio of $\mu_e$ and $\mu_n$ is of order of $10^3$.