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-tokeeper
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 an equivalent or
better effective field and field gradient.
A noise plateau for intermediate recording densities is observed for a recording layer of typical magnetization. Medium noise characteristics and transition jitter in
perpendicular magnetic recording are explored using micromagnetic simulation. The
plateau is replaced by a normal linear dependence of noise on recording density for a
low magnetization recording layer. We show analytically that a source of the plateau is
similar to that producing the Non-Linear-Transition-Shift of signal. In particular,
magnetostatic effects are predicted to produce positive correlation of jitter and thus
negative correlation of noise at the densities associated with the plateau.
One focus for developing perpendicular recording media is on how to extract
intergranular exchange coupling and intrinsic anisotropy field dispersion. A micromagnetic numerical technique is developed to effectively separate the effects of
intergranular exchange coupling and anisotropy dispersion by finding their correlation
to differentiated M-H curves with different initial magnetization states, even in the
presence of thermal fluctuation. The validity of this method is investigated with a series
of intergranular exchange couplings and anisotropy dispersions for different media
thickness. This characterization method allows for an experimental measurement
employing a vibrating sample magnetometer (VSM).
Bit patterned media have been suggested to extend areal density beyond 1
Tbit/in2. The feasibility of 4 Tit/in2 bit patterned recording is determined by aspects of
write head design and media fabrication, and is estimated by the bit error rate.
Micromagnetic specifications including 2.3:1 BAR bit patterned exchange coupled
composite media, trailing shield, and side shields are proposed to meet the requirement
of 3×10-4 bit error rate, 4 nm fly height, 5% switching field distribution, 5% timing and
5% jitter errors for 4 Tbit/in2 bit patterned recording. Demagnetizing field distribution is
examined by studying the shielding effect of the side shields on the stray field from the
neighboring dots. For recording self-assembled bit-patterned media, the head design
writes two staggered tracks in a single pass and has maximum perpendicular field gradients of 580 Oe/nm along the down-track direction and 476 Oe/nm along the crosstrack
direction. The geometry demanded by self-assembly reduces recording density to
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