The Micromagnetic Study Of The Media Microstructure And The Recording Process Of The Future Recording Modes

During2004to2006，the industry of hard disk drive switched from longitudinalmagnetic recording (LMR) to perpendicular magnetic recording (PMR). However, withthe continual increase of areal density, PMR will approach its superparamagnetic limit.The study of new magnetic recording modes is imperative. Energy assisted magneticrecording (EAMR), bit patterned magnetic recording (BPMR) and Shingled magneticrecording (SMR) are the three recording modes to achieve the density above1Tbit/in2.The three magnetic recording modes need different media designs with differentmagnetic parameters and microstructures, and their own recording processes are alsodifferent. In this thesis, under comprehensive consideration of thermal stability, signalto noise ratio (SNR) and writeability, the media, recording process and density limit ofBPMR and SMR are studied. The effect of twin structure in L10FePt medium used byEAMR on magnetic recording properties is also analyzed.Based on the measured five-fold twin structure in L10FePt nanoparticle, ananalytical model is established to study the effect of twin structure on the anisotropyfield of nanoparticle. The calculation indicates that the existence of twin structure willconsiderably reduce the anisotropy field and cause a wide distribution of the anisotropyfield, which will decrease the thermal stability of FePt medium, broaden the switchingfield distribution, and decrease SNR. This study has general significance on the Hkdistribution in HDD media.A Two-particle model is used to study the switching properties of exchangecoupled composites (ECC) media, and analyze the relationship between the switchingfield and the media magnetic parameters. The results will help the design of ECC mediawhich has both good thermal stability and writeabilty. Then, shingled magneticrecording is carried out on the conventional thin film media and ECC media,respectively. SNR of both media at different recording densities is studied, and it isfound that ECC media has a higher SNR and a higher density limit. The magneticparameters of ECC media are further optimized to attain a higher SNR.The recording processes in BPM fabricated by lithography or by ion irradiation aresimulated. In the lithography prepared BPM, the time window for the correct written-inand the tolerance of the offset margin can be attained. We find that the distribution of anisotropy field caused by the inhomogenity of thin film can deteriorate the correctwritten-in and should be reduced for optimum performance. For the recording processof BPM fabricated by ion irradiation, it is recognized that the significant reduction ofmagnetic properties in the irradiated area and the magnetic isolation among bits are thekeys to realize the correct written-in. Through optimizing the system and magneticparameters of BPMR, the recording density limit of BPM fabricated by ion irradiation ispredicted to be3.0Tbit/in~2.