The Induced Magnetic Anisotropy in Evaporated Films of Nickel-Iron Alloys

Abstract

The theories of the magnetic anisotropy of polycrystalline nickel-iron films in the permalloy region of composition are briefly reviewed. A simple model is then described for the magnetic anisotropy which can be induced in such films during evaporation. This model includes the sum of the effects of iron-pair directional ordering and a constant linear stress lying along the annealing field. After a detailed description of the experimental technique used to prepare NiFe films about 1500Å thick in the region of composition 80-85% nickel, the results of observations of the hysteresis loops measured at 400 c/s are used to derive values of the anisotropy field Hk which are then compared with the values expected should the simple model apply. The experimental observation that increasing the substrate temperature moves the minimum in anisotropy energy to lower nickel content in the film is supported by the simple model. When the complicating effects of fibre growth are included, the major features of the observations are found to agree quite well with the model but the behaviour of the induced anisotropy is shown to be complex and the possibility of contributions due to imperfection ordering are discussed