Computer simulation of magnetic recording materials

Abstract

As an external memory device, hard disk drive (HDD) is the most commonly used. Amount of information for storage is ever increasing year by year. To meet this demand, recording density is increasing in every year. In this thesis, recording performance of double layered perpendicular media were studied by micromagnetic simulation method in the first part to search the possibility of extremely high recording density and Heusler alloys with high spin polarization were invested by first principle calculation method in the second part in order to explore the possibility of utilizing these as a read head sensor in HDD head. Firstly, micromagnetic treatments of recording physics can reveal detailed information on the medium magnetization process during recording, the write head field, and even the response of magneto-resistive sensors during reproducing process. The understanding of the magnetic dynamics during the recording process is becoming increasingly important for high end recording achievement. In order to achieve ultra-high density, it is necessary to make the media with enhanced signal to noise ratio (SNR) characteristics and high thermal stability. In the first part, effect of grain size distribution of the recording layer on SNR and thermal stability was examined by using Voronoi cell to simulate real grain configuration. Magnetostatic interaction between recording layer and soft underlayer (SUL) contributes substantially on increase of noise in reproduction process, unlike single layered perpendicular magnetic recording media. Therefore, the noise reduction in the double layered media becomes an important issue. To reduce the noise from SUL, we propose a modified medium with a antiferro coupled SUL of two soft magnetic layers separated by a thin non-magnetic Ru layer, multi-layered SUL, and intergranular decoupled SUL. Modified SUL can reduce the transition jitter compared with conventional SUL and multi-layered SUL has the best SNR among them. For high K...