Spatial Evolution of the Ferromagnetic Phase Transition in an Exchange Graded Film
Brian J. Kirby, H. F. Belliveau, D. D. Belyea, Paul A. Kienzle, Alexander J. Grutter, P. Riego, A. Berger, Casey W. Miller
A combination of experiments and numerical modeling was used to study the spacial evolution of the ferromagnetic phase transition in a thin film engineered to have a smooth gradient in exchange strength, and thus effectively a gradient in local transition temperature. For a NixCu1-x alloy film with depth-dependent Ni concentration, we observe that the entirety of the sample is magnetically ordered at low temperatures, and that a mobile boundary separating ordered and disordered regions emerges as temperature is increased. We demonstrate continuous control of the boundary position with temperature, and control of the magnetically ordered sample volume with magnetic field. This functionality is observed near room temperature, and may enable a variety of novel thermomagnetic applications.