Controlling magnetic anisotropy in nickel films on LiNbO3

Abstract

Nickel thin films, deposited on 128° Y-cut LiNbO3, and subsequently annealed at low temperature (≈ 300 °C), exhibit a number of interesting and unusual magnetic properties. These include: hysteresis branch crossings, negative Barkhausen jumps, square hysteresis loops (squareness > 0.99), Stoner-Wohlfarth behavior, and a well-defined, uniaxial, magnetic anisotropy. Previous work suggests the magnetic anisotropy is created by magneto-elastic coupling between the film and the underlying substrate. The difference of thermal coefficient of expansion between film and substrate was thought to generate a well-defined strain upon cooling from the annealing temperature. Here we show that the changes in the effective magnetic anisotropy field are directly correlated with thermal strain. This mechanism provides a technique for creating and modifying magnetic anisotropy in a controlled fashion.