Uniaxial in-plane magnetic anisotropy and exchange bias in Sm/Fe bilayers

Abstract

We have studied structural and magnetic properties of quartz/Sm(25 nm)/Fe(15 nm) thin films by grazing incidence x-ray diffraction, atomic force microscopy, longitudinal magneto-optic Kerr effect, and superconducting quantum interference device magnetometry. Both Sm and Fe layers exhibit growth in a preferential direction with textured granular structure. The Fe layer is composed of small elongated grains (36 nm long and 21 nm wide). The Fe grains are monodomains and are all parallel aligned due to the texture effect. Therefore, their magnetic shape anisotropy is summed, producing a final uniaxial in-plane magnetic anisotropy in the film. The Sm/Fe system is an antiferromagnetic/ferromagnetic bilayer exhibiting exchange bias coupling below 40 K. The long-range character of Sm-Fe spin interaction located near the interface maintains this coupling, in spite of disorder effects at the interface, such as Sm-Fe alloying, and results in a power-law decay with temperature for the exchange bias field ${(H}_{E})$.