Investigations of the Effects of Neutron and He3 Irradiation on the Magnetic Properties of Permalloy Thin Films

Abstract

Measurements have been made of the changes in the magnetic anisotropy energy and hysteresis loop parameters of evaporated Permalloy thin films resulting from 2.2‐MeV He³ irradiation and from reactor neutron irradiation. Only minor changes were observed following an irradiation of 1.6×10¹⁴ He³ particles/cm². However, a total irradiation of either approximately 10¹⁷ neutrons/cm², or 8 to 9×10¹⁶ He³ particles/cm², yielded the following general results: Regardless of the magnetic state of the sample, the uniaxial anisotropy energy K_u increased (up to 200%) when irradiations took place in zero applied field. Similar increases were noted as a result of either neutron irradiation with a saturating magnetic field along the easy axis or He³ irradiation with a saturating magnetic field either parallel or perpendicular to the easy axis. A decrease of ∼50% in K_u resulted from neutron irradiation when the saturating magnetic field was applied perpendicular to the easy axis. Rotation of the easy axis, up to 78°, occurred for either neutron or He³ irradiation with a saturating magnetic field applied perpendicular to the easy axis. The more significant hysteresis loop modifications observed were the development of constricted loops (measured in the hard direction) for most of the samples irradiated in zero applied field, and decreases in the coercive force up to 28% (measured in the easy direction) of most of the irradiated samples.