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

We have measured the pressure dependence of the Fe57 nuclear magnetic resonance frequency ν in ferromagnetic iron from 1–10 000 kg/cm2 at −77°C, 0°C, and 84.2°C. From these measurements the volume dependence of ν has been obtained, enabling us to correct measurements of ν(T)P = 1 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 σ, we have found that, at constant volume, the hyperfine coupling constant A in the relation ν = Aσ is an explicit function of the temperature. Thus, measurements of the temperature dependence of ν, even when corrected to constant volume, do not give accurately the temperature dependence of σ. The results of a theory based on Stoner's collective electron model for the delectrons are presented to account for the temperature dependence of A.