Zhanjie Li

Write field asymmetry in perpendicular magnetic recording

We present a systematic study of write field asymmetry by using micromagnetic modeling for a perpendicular magnetic recording (PMR) writer structure. Parameters investigated include initial magnetization condition, write current amplitude, write current frequency, and initial write current polarity. It is found that the write current amplitude and frequency (data rate) are the dominant factors that impact the field asymmetry. Lower write current amplitude and higher write current frequency will deteriorate the write field asymmetry, causing recording performance (such as bit error rate) degradation.

Degaussing PMR Writer Poles: A Micromagnetic Modeling Study

This paper presents a study of the degauss process of a perpendicular magnetic writer pole using micromagnetic modeling as a tool. The dynamics of the yoke and the pole-tip magnetization relaxation during degauss are studied in detail, and the remanent field of the pole tip is used as a metric to measure the effectiveness of each of the degauss methods. Various aspects of the degauss current waveforms are investigated, such as frequency, duration, initial current amplitude, amplitude decay envelope, and overshoot. Some alternative waveforms, i.e., unipolar reverse pulse degaussing, have also been examined. It has been found for many of the parameters to have an optimal range outside of which the degauss effectiveness and efficiency are degraded.

Characteristics of magnetic force microscopy magnetics on high moment perpendicular magnetic recording writers with high coercivity probes

High resolution magnetic force microscopy (MFM) imaging with high coercivity probes on perpendicular magnetic recording (PMR) writers directly characterizes magnetic field contour for the writer main pole as well as its shields’ magnetic state. Evolution of write bubble and return field was analyzed by MFM imaging in dynamic phase detection scheme. Different write field components and their out of plane second order derivatives were calculated via finite element modeling. The MFM imaged write field distribution correlates well with the PMR writer out of plane write field component. Magnetic responses of the PMR writer main pole, trailing and side shields are quantified. The trailing and side shields exhibit complicated magnetic saturation behaviors comparing with the PMR writer pole. The side shield’s magnetic response is dependent upon its initial equilibrium state.

Temporal and Spatial Field Dynamics in Shielded Writer: A Micromagnetic Modeling Study

The characteristics of spatial and temporal field distributions are presented for wrap-around-shielded perpendicular magnetic recording writers. Micromagnetic modeling simulations are conducted to study the effects of shield thickness and the magnetization on the shield-related side field. An improvement of side field is found with the thicker shield thickness and higher saturation magnetization. The maximum side field is spatially and time dependent during the dynamic writing process. The side field reaches the maximum around the transitions, where the write field from the main pole is at the minimum. In addition, the write current rise-time effect on the side field is investigated.

Write Field Dynamics in the Presence of Antiferromagnetic Coupling of Writer Pole

A micromagnetic simulation is conducted to study the write field dynamics in the presence of antiferromagnetic exchange coupling (AFC) of writer pole for a perpendicular magnetic recording (PMR) writer head. It is found that, depending on the actual configuration of the AFC coupling in the yoke and the pole tip, there could be an intermediate transient state near zero write field during the magnetization reversal, compared to the normal writer design without AFC coupling. This transient state may cause recording performance degradation. We further investigated the AFC coupling effect on the remanent field in the degauss process. For different performance aspects, i.e., field dynamics, maximum field, and remanent field, the AFC in the yoke and in the pole tip plays different roles.

Modeling magnetic column intermediate layer of perpendicular magnetic recording

A computational study of the head field was presented in a specific head/media configuration, where the intermediate layer (IL) consists of the periodic magnetic columns and Ru columns. It was found that the head field increases with the thicker and wider magnetic columns. Micromagnetic simulation shows that this approach is to achieve a lower effective IL thickness for enhancing the write field by replacing some Ru grains with the columnar magnetic material without reducing the IL thickness.

Evaluation of High Data Rate Performances of PMR Components

An effort has been made on evaluating magnetic and electrical performances of perpendicular recording (PMR) components at high recording data rates (2.0-3.0 Gbit/s). In general, a fully functional PMR recording subsystem up to 3.0 Gbit/s has been demonstrated experimentally in spin-stand testing by using product recording heads, media, preamps, and channels. Particularly, we studied the influence of the novel pole structures of recording heads on the high data rate performances. The obtained experimental results show that the novel pole structure design of recording write head has some significant impact on the performance of the bit error rate, write ability, and other parametric data at high data rate situations.