Influence of Neutron and Argon Ion Bombardment on the Induced Uniaxial Anisotropy in Nonmagnetostrictive Permalloy Films

Technical magnetic thin films evaporated at 150°, 300°, or annealed at 550°C were bombarded by pile neutrons and 11-keV argon ions in a magnetic field at 200°C. After a sufficiently long bombardment time the uniaxial anisotropy constant attains for all films the same saturation value. The experimental data are well explained by supposing this value to be due to the simultaneous presence of directional pair ordering and partial long-range Ni3Fe type order. Long-range order seems to exist already in films deposited at 300°C whilst in the other cases it is created during bombardment. Films condensed at 150°C show an extra component of magnetic anisotropy, probably due to the ordering of lattice imperfections, which disappears during bombardment or annealing. Comparison of the saturation values of induced anisotropy obtained after neutron and argon-ion bombardment shows that the degree of atom-pair order obtained, decreases with increasing number of displacements per second and per atom of the target.