Study of graded-medium properties of process, structure, magnetism, and magnetic recording
Date Issued
2014
Date
2014
Author(s)
Lin, Yi-Hung
Abstract
Magnetic recording needs to have high remanent magnetization and high coercivity due to the effects of self-demagnetization and stray fields. Accordingly, in the past CoCrPt was used for the material of recording medium. However, because of larger thermal fluctuation and noise, it is hard to further enhance the areal density if the areal density approaches to 1 Tbit/in2. L10-FePt becomes one of the candidate materials due to the high magnetocrystalline anisotropy constant (Ku ~ 7×107 erg/cm3), high saturation magnetization (~1140 emu/cm3), high anisotropy field (~116 kOe), and minimal stable grain size as small as 3 nm. Therefore, FePt is employed as the material of recording media to be studied. Such high Ku materials also makes writing difficulty resulting to develop the technology of heat-assisted magnetic recording (HAMR) in order to solve the problems of large writing field. The other way is to reduce the switching field. In the past, double-layer of exchange spring media have been used as the recording media to reduce the coercivity by a factor of 2. Our studies concentrate on graded media in order to further decrease the coercivity and maintain the thermal stability factor.
Herein, we explore the magnetic behaviors of L10-FePt graded films three approaches: gradient-temperature (Tg), composition (Cg) and working pressure (Pg). As a result, Hc⊥ can be reduced by a factor of 2.6, 2.8, and 3.3 for the Cg-, Tg- and Pg-L10 FePt layers, respectively. Both Tg- and Pg-FePt have the similar reversal behavior. On the other hand, for Cg-FePt, the magnetization increases sharply upon removal of the applied field. This increment in the magnetization is due to the presence of reversible magnetization switching arising from the non-coherent rotation. Therefore, considering to reduce the switching field and magnetic reversal, Pg-FePt film may has the best gradient performance among these three structures.
Subjects
梯度媒體
磁性膜
多層膜
金屬與合金
異向性
X光繞射
磁性量測
Type
thesis
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