Ferromagnetic Metals in High Magnetic Fields

High‐field susceptibility results are presented for Mössbauer measurements on iron at low temperatures in fields up to 135 kOe and magnetization measurements on iron and nickel single crystals in fields up to 148 kOe with vibrating sample magnetometers. The Mössbauer measurements give the hyperfine field H_n= H_int− (H₀−H_DM)+ΔH, where H_int is the hyperfine field at zero applied field, H₀ is the applied field, H_DM is the demagnetizing field, and ΔH is a term which would reflect a change in the magnetization at high field, i.e., ΔH/H_n=ΔM/M. The Mössbauer results at 4.2°K are equivalent to χ=2±7×10⁻⁵ emu/cc. The magnetization experiments give χ≤4×10⁻⁵ for iron and χ≤1.1×10⁻⁵ for nickel at 4.2°K. We discuss the various contributions to the total susceptibility χ, give estimates of χ_d based on theoretical band calculations, and discuss various uncertainties in both the theoretical calculations and in values of the molecular field parameter which make detailed comparisons difficult. Finally, we compare with predictions based on Herring's phenomenological description of χ for ferromagnets.