R&D: Anisotropic Exchange Spin Model to Investigate Curie Temperature Dispersion of Finite-Size L10-FePt Magnetic Nanoparticles

ArXiv has published an article written by Kohei Ochiai, Tomoyuki Tsuyama, Sumera Shimizu, Resonac Corporation, Research Center for Computational Science and Informatics, 8, Ebisu-cho, Kanagawa-ku, Yokohama, Kanagawa. 221-8517, Japan, Lei Zhang, Jin Watanabe, Fumito Kudo, Resonac Hard Disk Corporation, Research & Development Center, 5-1, Yawatakaigan-dori, Ichihara, Chiba, 290-0067,Japan, Jian-Gang Zhu, Data Storage Systems Center, Carnegie Mellon University, Pittsburgh, PA 15213, USA, Electrical and Computer Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA, and Materials Science and Engineering Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA, and Yoshishige Okuno, Resonac Corporation, Research Center for Computational Science and Informatics, 8, Ebisu-cho, Kanagawa-ku, Yokohama,Kanagawa. 221-8517, Japan.

Abstract: “We developed an anisotropic spin model that accounts for magnetic anisotropy and evaluated the Curie temperature (Tc) dispersion due to finite size effects in L10-FePt nanoparticles. In heat-assisted magnetic recording (HAMR) media, a next-generation magnetic recording technology, high-density recording is achieved by locally heating L10-FePt nanoparticles near their Tc and rapidly cooling them. However, variations in Tc caused by differences in particle size and shape can compromise recording stability and areal density capacity, making the control of Tc dispersion critical. In this study, we constructed atomistic LLG models to explicitly incorporate the spin exchange anisotropy of L10-FePt, based on parameters determined by first-principles calculations. Using this model, we evaluated the impact of particle size on Tc dispersion. As a result, (1) the Tc dispersion critical to the performance of HAMR can be reproduced, whereas it was previously underestimated by isotropic models and (2) approximately 70% of the experimentally observed Tc dispersion can be attributed to particle size effects. This research highlights the role of exchange anisotropy in amplifying finite-size effects and underscores the importance of size control in HAMR media.“