R&D: Microstructure and Magnetic Properties of Ultrathin FePt Granular Films

AIP Advances has published, an article written by Yuepeng Zhang, Western Digital Media, LLC, 1710 Automation Parkway, San Jose, California 95131, USA, Alan Kalitsov, Western Digital Technologies, Inc., 1710 Automation Parkway, San Jose, California 95131, USA , Jim Ciston, National Center for Electron Microscopy – Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA, Oleg Mryasov, Western Digital Technologies, Inc., 1710 Automation Parkway, San Jose, California 95131, USA, Burak Ozdol, Jiangtao Zhu, Shikha Jain, Bing Zhang, Western Digital Media, LLC, 1710 Automation Parkway, San Jose, California 95131, USA, Boris Livshitz, Western Digital Technologies, Inc., 1710 Automation Parkway, San Jose, California 95131, USA, Alexander Chernyshov, Antony Ajan, Paul Dorsey, Western Digital Media, LLC, 1710 Automation Parkway, San Jose, California 95131, USA, Gerardo Bertero, Western Digital Technologies, Inc., 1710 Automation Parkway, San Jose, California 95131, USA, Ramamurthy Acharya, Andrea Greene, and Sharon Myers, Western Digital Media, LLC, 1710 Automation Parkway, San Jose, California 95131, USA.

Abstract: “FePt granular films with grain size smaller than 10nm are promising candidates for storage media used in the next generation heat-assisted magnetic recording technology. However, FePt films show degraded magnetic properties when the grain size is reduced to this scale, which cannot be explained solely by the finite size theory. In this study, we explored the structural cause of property degradation by employing advanced electron microscopy and atomistic modeling. Structural features unique to the nanostructured FePt granular films at significantly reduced grain sizes of 2∼8nm were studied by high-resolution scanning transmission electron microscopy with geometric aberrations corrected up to the third order. Two critical structural parameters, the threshold grain size corresponding to the upper size limit of the FePt grains with zero chemical ordering and the sub-nanometer thin interfacial impurity at grain boundaries, were identified. A new atomistic model was developed to correlate these structural characteristics with key magnetic properties such as Curie temperature, saturation magnetization, magnetocrystalline anisotropy, and their grain-to-grain variation. The model shows good agreement with the experimental magnetic data and explains the gap in magnetic properties between the bulk and nanostructured FePt.“