High-voltage electron microscope observation of stripe domains in permalloy films evaporated at oblique incidence

Abstract

A series of permalloy films of composition 83% Ni-17% Fe was prepared with thicknesses in the range 1500–3000 Å. The rate of evaporation was 2–14 Å/sec at a pressure of 3 × 10 -5 to 5 × 10 -6 torr. The angle between the vapour beam and the normal to substrate was varied from 0° to 80°. The samples were investigated in the Cavendish High Voltage Electron Microscope operating at 500 kV. Stripe domains were observed at all angles of the incident vapour beam independent of the type of substrate used. For samples evaporated at angles 0°–40° the stripe domains appeared in localised regions, their direction being parallel to the domain walls and perpendicular to the direction of the incident vapour beam. In the 50° and 60° films the very regular stripe domains were present over the whole film and were parallel to the inclusion shadow; however at 70° the stripe domains were no longer unidirectional. On increasing the angle of incidence to 80° the stripe domains once again became directional, but the domain structure was not as regular as in 50° and 60° films. The observations on the stripe domain structure can be separated into four groups according to the angle of incidence at which the films were evaporated, (a) 0°–40°, (b) 50°–60°, (c) 70°, (d) 80°. A tentative explanation of this variation with angle of incidence is discussed in terms of the differing relative contributions produced by the perpendicular and parallel induced anisotropies.