Magnetization reversal in a preferred oriented (111) L10 FePt grown on a soft magnetic metallic glass for tilted magnetic recording

Abstract

L10 FePt is an important material for the fabrication of high density perpendicular recording media, but the ultrahigh coercivity of L10 FePt restricts its use. Tilting of the magnetic easy axis and the introduction of a soft magnetic underlayer can solve this problem. However, high temperature processing and the requirement of epitaxial growth conditions for obtaining an L10 FePt phase are the main hurdles to be overcome. Here, we introduce a bilayered magnetic structure ((111) L10 FePt/glassy Fe71Nb4Hf3Y2B20/SiO2/Si) in which the magnetic easy axis of L10 FePt is tilted by ∼36° from the film plane and epitaxial growth conditions are not required. The soft magnetic underlayer not only promotes the growth of L10 FePt with the preferred orientation but also provides an easy cost-effective micro/nanopatterning of recording bits. A detailed magnetic characterization of the bilayered structure in which the thickness of (111) L10 FePt with the soft magnetic Fe71Nb4Hf3Y2B20 glassy underlayer varied from 5 to 60 nm is carried out in an effort to understand the magnetization switching mechanism. The magnetization switching behavior is almost the same for bilayered structures in which FePt layer thickness is >10 nm (greater than the domain wall thickness of FePt). For FePt film ∼10 nm thick, magnetization reversal takes place in a very narrow field range. Magnetization reversal first takes place in the soft magnetic underlayer. On further increase in the reverse magnetic field, the domain wall in the soft magnetic layer compresses at the interface of the hard and soft layers. Once the domain wall energy becomes sufficiently large to overcome the nucleation energy of the domain wall in L10 FePt, the magnetization of the whole bilayer is reversed. This process takes place quickly because the domain walls in the hard layer do not need to move, and the formation of a narrower domain wall may not be favorable energetically. Our results showed that the present bilayered structure is very promising for the fabrication of tilted bit-patterned magnetic recording media.