Dependence of Magnetic Anisotropy on the Crystal Structure of Ni–Fe Thin Films

Abstract

The induced magnetic anisotropy of Ni–Fe films has been shown to be related to the crystal structure of the film. By use of electron diffraction, the crystal structure of vacuum‐deposited films was determined over the composition range 5% to 85% Ni, with substrate temperature during deposition at various temperatures in the range 25° to 500°C. The films were deposited on single‐crystal NaCl substrates. The phase diagram determined in this way has boundaries which are in fair agreement with the equilibrium boundaries for bulk material above 400°C and deviate markedly below 300°C. The (α+γ) mixture phase disappears below 100°C. Although epitaxial growth occurs at high temperatures, the existence or absence of epitaxy has no significant effect on the type of crystal growth. Comparison of these data with measured values of the anisotropy energy indicates that the anisotropy is strongly sensitive to structure. The anisotropy energy for γ structure is about 2½ times larger than for α structure at the composition where the anisotropy can be measured for the α structure and extrapolated with reasonable confidence for the γ structure. Others have proposed pair ordering as an important source of anisotropy because of an apparent peak in the anisotropy energy at 50% Ni composition. The present work shows that there is no such peak, and therefore pair ordering cannot be a dominant contributor.