Spin structure in perpendicularly magnetized Fe-FePt bilayers

Abstract

We studied the exchange-spring behavior in FePt-Fe hard-soft magnetic heterostructures. We present a study of the spin structure of the soft Fe layer of Fe-FePt bilayers by nuclear forward scattering of synchrotron radiation. The orientation of the Fe moments close to the top of the soft layer was determined quantitatively as a function of the soft-layer thickness. We show that for a few monolayers of Fe, the magnetically hard FePt layer pins the magnetization in the soft Fe layer to the out-of-plane direction. With increasing Fe-layer thickness, the influence of the FePt diminishes and the magnetization cants toward the in-plane Fe[001] direction. The significance of the exchange coupling constant as the relevant parameter for the exchange-spring behavior is demonstrated by one-dimensional micromagnetic simulations.