Promises and Challenges: Recent Development of Granular FePt-L10 Thin Film Material for Heat Assisted Magnetic Recording

Abstract

At room temperature, perpendicularly ordered L10FePt thin film exhibits extremely high uniaxial anisotropy with easy axis oriented along the ordering direction [1]. The relatively low curie temperature and high temperature gradient of the anisotropy field near the Curie point of the L10 FePt makes it almost perfect as a recording media for heat assisted magnetic recording (HAMR) technology [2-5]. In HAMR, an optically (by laser illumination) excited plasmonic near field transducer provides localized electric field to the recording media as schematically shown in Figure 1. The localized alternating electric field at optical frequency generates rapid electronic motion in the metallic magnetic grains of the recording medium underneath, heating up the grains over their Curie temperature. As the medium moves away from the NFT, thereby, the localized electric field, the temperature start to cool down, the medium grains start to regain its magnetization with orientation guided by the recording head field. As the temperature of the medium grains decreases, the magnetic anisotropy of the grains quickly rises. When it exceeds the capability of the recording field, the magnetization direction freezes [6]. In order to insure sharp magnetic transitions between recorded bits, the lateral size of medium magnetic grains needs to be small with thermally insulating grain boundaries. A relatively thick heat sink layer is placed underneath the magnetic layer to facilitate a high thermal gradient, currently at 10K/nm, which is essential to suppress the transition jitter caused by grain-to-grain Curie temperature variation in the media [7-10].