Nuclear Magnetic Specific Heat in Two Ferromagnetic Iron Alloys

From the nuclear magnetic specific heat, measured at 1.6° to 4.2°K, $H_{\mathrm{eff}}$ at the Co nuclei in ${\mathrm{Co}}_{0.3}$ ${\mathrm{Fe}}_{0.7}$ was calculated to be 312 koe, while $H_{\mathrm{eff}}$ at the V nuclei in ${\mathrm{V}}_{0.33}$ ${\mathrm{Fe}}_{0.67}$ is 61 koe, or less. Both of these alloys are body-centered cubic and ferromagnetic. The large difference in the $H_{\mathrm{eff}}$ values may be associated with the fact that in ${\mathrm{Co}}_{0.3}$ ${\mathrm{Fe}}_{0.7}$ the ${\mathrm{Co}}^{59}$ nucleus is located in an atom with appreciably polarized $3d$ electrons, while in ${\mathrm{V}}_{0.33}$ ${\mathrm{Fe}}_{0.67}$ the ${\mathrm{V}}^{51}$ nucleus is the only abundant nuclide with a nuclear magnetic moment and the atomic moment of V is very small or zero. Since in ferromagnetic alloys the polarization of the core $s$ electrons is expected to be much stronger in those atoms which do have polarized $d$ electrons than in adjacent atoms which do not, the above results suggest that, in the alloys investigated, the dominant contribution to $H_{\mathrm{eff}}$ arises through Fermi contact interaction from the polarization of the core $s$ electrons, as found for iron by Hanna et al.