Evidence of Long-Range Order in 3He-Irradiated Permalloy Films

Abstract

Room-temperature measurements of the uniaxial anisotropy energy Ku have been made on a series of vacuum-deposited thin polycrystalline Permalloy films following 3He particle irradiations at temperatures of 125°, 200°, 250°, and 300°C. The results indicate the development of two types of long-range order, in addition to the so-called Fe–Fe atom pair short-range directional ordering: an NiFe-type order similar to that reported for neutron-irradiated bulk Permalloy, which enhances Ku for compositions around 50% Ni–50% Fe, and the well-known Ni3Fe-type order, which develops at the expense of Fe–Fe atom pair ordering, for compositions in the neighborhood of 75% Ni–25% Fe. The maximum value of Ku obtained due to NiFe long-range order is at least an order-of-magnitude less in the thin film than in the neutron-irradiated bulk Permalloy; also, the irradiation temperature at which Ku ceases to be enhanced by the development of NiFe long-range order in the thin film is well below the ordering temperature reported for bulk samples. For films with compositions off the NiFe and Ni3Fe stoichiometry, the temperature dependence of Ku was found to be in good agreement with the (Tc-Ta) behavior as suggested for Fe–Fe atom pair short-range directional ordering.