Pressure and Temperature Dependence of the Fe57 Nuclear Magnetic Resonance Frequency in Ferromagnetic Iron

We have measured the pressure dependence of the ${\mathrm{Fe}}^{57}$ nuclear magnetic resonance frequency $\nu$ in ferromagnetic iron from $\text{1–10\hspace{0.17em}000\hspace{0.17em}}\mathrm{kg}/{\mathrm{cm}}^2$ at −77°C, 0°C, and 84.2°C. From these measurements the volume dependence of $\nu$ has been obtained, enabling us to correct measurements of ${\mathrm{\nu (T)}}_{\text{P\hspace{0.17em}=\hspace{0.17em}1\hspace{0.17em}}\mathrm{atm}}$ for the effects of thermal expansion. By making a similar correction for the effect of thermal expansion on the temperature dependence of the saturation magnetization $\sigma$ , we have found that, at constant volume, the hyperfine coupling constant $A$ in the relation $\mathrm{\nu \hspace{0.17em}=\hspace{0.17em}A\sigma }$ is an explicit function of the temperature. Thus, measurements of the temperature dependence of $\nu$ , even when corrected to constant volume, do not give accurately the temperature dependence of $\sigma$ . The results of a theory based on Stoner's collective electron model for the d electrons are presented to account for the temperature dependence of $A$ .