Influence of exchange on signal-to-noise ratio in [CoX/Pt]4 media

Zhen Zhao,Dan Wei,Longze Wang,Jiangnan Li

doi:10.1063/1.4978457

Abstract

In longitudinal hard disk drives, the medium Signal-to-Noise Ratio (SNR) is higher with better grain segregation or lower inter-grain exchange. In current energy assisted magnetic recording system, multilayer perpendicular media are utilized; thus, it is significant to study the influence of grain segregation on SNR, as well as the relevant percolation phenomenon, to give suggestions on the recording media design. In this study, micromagnetic recording models of Microwave Assisted Magnetic Recording (MAMR) is built up to calculate SNR to find optimized [CoX/Pt]4 media parameters such as the inter-grain exchange Agb and the anisotropy orientation distribution αθ, with different field generation layer (FGL) saturation in the spin torque oscillator (STO). The constrained relationship between Agb and αθ in MAMR have been estimated, and the medium SNR will be optimized in the perpendicular [CoX/Pt]4 with a proper but not lowest exchange.

Highlights

Present perpendicular recording (PR) has only about 10 grains in a bit, almost 1/10 of the magnitude compared to the previous longitude recording.[1,2] In order to improve recording Signal-to-Noise Ratio (SNR) at higher linear density, writing noise origin such as transition percolation and head shift have been widely studied
The media perpendicular M-H loop is illustrated in Fig.1a, the 4-layer media has a high coercivity of 12 kOe and saturation field of 18 kOe, which meet the requirement of high density recording media
It should be noted that, as the media saturation is Bs=15 kOe, the relative small coercivity Hc is due to the self-demagnetization perpendicular to CoPt media strongly offset the effect of anisotropy

Summary

INTRODUCTION

Present perpendicular recording (PR) has only about 10 grains in a bit, almost 1/10 of the magnitude compared to the previous longitude recording.[1,2] In order to improve recording SNR at higher linear density, writing noise origin such as transition percolation and head shift have been widely studied. Side-track percolation noise under PR condition is mainly caused by head partial erase[3] and the granular magnetic properties,[4,5,6] and it can be decreased by enhancing intergranular separation, i.e. increasing the homogeneity of intra-grain anisotropy orientation distribution or decreasing the inter-grain exchange interaction.[7,8] The CoCrPt metallic oxide thin film separated by SiO2 non-ferromagnetic oxide has been used for the PR media, with its coercivity of above 6 kOe.[9].

MICROMAGNETIC RECORDING MODELS

RESULTS AND DISCUSSIONS

CONCLUSION