Micromagnetic Study of Perpendicular Magnetic Recording Media a Dissertation Submitted to the Faculty of the Graduate School of the University of Minnesota by Yan Dong in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

introducing me to the field of magnetic recording and supervising me to do these exciting projects. This would be impossible without his guidance and encouragement in my scientific pursuit. I would like to thank him for his valuable comments and helpful discussions on my research. His academic insights, profound understanding of magnetic materials and micromagnetic theory always guided me to go deeper and be more active. I learned a lot from him. I would also like to acknowledge the input and advice from Professor Jian-ping Wang, Beth Stadler and Jack Judy during my work and stay in MINT center. for their time, help and efforts of serving in my committee. It has been an enjoyable experience with the past and current members of Professor Victora's group and the MINT center. I would like to thank Xiao Shen, and many other friends for their valuable discussion and friendly feedback. I enjoyed the time I spent with them. I would also like to acknowledge Seagate Technology, INSIC EHDR and IDEMA/ASTC for funding and the supercomputing institute of the University of Minnesota for computer time. Finally, I would like to express my love and thanks to my parents, my grandparents and my boyfriend. Without their love, support and advice, I would have never gone so far. ii Dedication With gratitude to my parents. iii Abstract With increasing areal density in magnetic recording systems, perpendicular recording has successfully replaced longitudinal recording to mitigate the superparamagnetic limit. The extensive theoretical and experimental research associated with perpendicular magnetic recording media has contributed significantly to improving magnetic recording performance. Micromagnetic studies on perpendicular recording media, including aspects of the design of hybrid soft underlayers, media noise properties, inter-grain exchange characterization and ultra-high density bit patterned media recording, are presented in this dissertation. To improve the writability of recording media, one needs to reduce the head-to-keeper spacing while maintaining a good texture growth for the recording layer. A hybrid soft underlayer, consisting of a thin crystalline soft underlayer stacked above a non-magnetic seed layer and a conventional amorphous soft underlayer, provides an alternative approach for reducing the effective head-to-keeper spacing in perpendicular recording. Micromagnetic simulations indicate that the media using a hybrid soft underlayer helps enhance the effective field and the field gradient in comparison with conventional media that uses only an amorphous soft underlayer. The hybrid soft underlayer can support a thicker non-magnetic seed layer yet achieve …