Multiple diffraction effects in annealed permalloy films

Abstract

Transmission electron diffraction and electron microscope techniques have been used in studying the effects of annealing temperatures on the structure of thin Permalloy films. Single-crystal and polycrystalline films were epitaxially grown by vapor deposition of an (81% Ni, 19% Fe) alloy on heated freshly cleaved (100) faces of rocksalt. Annealing experiments, at temperatures between 300° and 700°C, were carried out in an electron diffraction instrument after the films had been floated off the rocksalt and mounted on 200-mesh Ni grids. The diffraction patterns of the single-crystal and polycrystalline as-grown and annealed films showed the effect of annealing twins on the number of extra reflections which appeared. The observed irrational spots and rings could be directly explained by the presence of twinning and double diffraction in a face-centered cubic structure. Weak reflections which appeared at forbidden (110) positions can be shown to result from double diffraction of (200), (020), and (002) positions, and are generated when {111} planes are textured and oriented in a [110] direction to the primary [100] orientation of the pattern. A dark-field electron microscopy study from these reflections further substantiates a double diffraction hypothesis. The reflections occur at temperature ranges below and above the critical ordering temperature for Permalloy and cannot be attributed to a superlattic structure. In addition, since annealing was carried out in vacuums in the high 10-7 Torr range, as well as in a reducing environment, the possibility that selective oxidation occurred was very unlikely. © 1967 The American Institute of Physics.