Structural and magnetic length scales in amorphous TbFe 2

Abstract

Magnetic phenomena in amorphous Tb–Fe thin films are related to structure on a variety of length scales. For instance, perpendicular magnetic anisotropy appears to be related primarily to short-range compositional and/or topological ordering. In this paper, we demonstrate that structure on longer length scales influences domain wall pinning and the morphology of the magnetic domains. Amorphous TbFe 2 films thicker than approximately 1 μ m that possess large perpendicular magnetic anisotropy have very long magnetic correlation lengths (50–70 nm, as determined previously by small-angle neutron scattering) and strongly asymmetric magnetic domains. Using small-angle X-ray scattering (SAXS), we show that such films show a well-defined structure with a characteristic length scale of approximately 57 nm. The structure of films grown at lower temperatures (with lower magnetic anisotropy K u but higher coercivity), shows a much broader distribution of length scales. We propose that the characteristic structure seen in SAXS is the source of domain wall pinning, which in turn determines the length scale of the magnetic domains, as well as the magnetic correlation length and coercivity. We also observe an in-plane anisotropy of the structure, which is likely related to the asymmetry of the magnetic domains and the anisotropy of the magnetic correlation length.