Sining Mao

Micromagnetic Analysis of Adjacent Track Erasure of Wrapped-Around Shielded PMR Writers

This paper presents a numerical analysis of adjacent track erasure (ATE) when operating wrapped-around shielded perpendicular magnetic recording (PMR) heads. Micromagnetic finite element modeling was used to investigate the magnetization dynamics in a PMR writer including a soft underlayer, and the resultant magnetic field in the recording layer. It is found that the ATE-field is an asymmetric and localized return field. Such an asymmetry is determined by the directions of both the magnetization in the pole tip and the initial magnetization in the WAS. The ATE-field is located near the corner and the inner edge of one side-shield. It is also found that the ATE-field remains strong for most of the time during write-field switching.

Effect of track asymmetry and curvature on shingle writing scheme

Written transition curvature in perpendicular magnetic recording is generally understood to result in increased transition jitter noise and degraded signal to noise ratio or byte error rate (BER) performance. For the shingle writing scheme, asymmetry or curvature in written tracks is considered inherent due to the erasure and track edge writing characteristics. It is proposed that such a track asymmetry is more prominent at high track density/smaller track pitch recording conditions. In this report we present spin stand experimental results to study the effect of the possible track asymmetry or curvature by shingle writing and reading back in different skews. By comparing shingle writing BER bathtub profiles in different writing skew conditions 0°, +/−2°, +/−4°, +/−6°, the effect of varying shingle track asymmetry and curvature is analyzed via subsequent skewed reading process. The shingle writing BER bathtub profiles as well as the read back amplitude cross track profile are generally symmetric upon one ...

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.

Reverse Overwrite Process in Shingled Recording Process at Ultrahigh Track Density

A systematic experimental study of reverse overwrite (ReOVW) process in the shingled recording scheme has been conducted in conjunction with characterization of corresponding recording performances from recording heads with different geometries. It was found that not only is there no ReOVW reduction as the track density increases, but also ReOVW is, in fact, slightly increased from 300 ktpi to 600 kpi or beyond by using the same writing conditions. These data suggest that conventional magnetic recording technology might be able to extend all the way beyond an areal density of one Tbit/in2 by using the shingled recording scheme.

Electrical low frequency random telegraph noise in magnetic tunnel junctions

Low frequency random telegraph noise (RTN) of electrical origin is reported in magnetic tunnel junction heads with ultrathin tunnel barriers (<1 nm). The RTN is characterized by abrupt and randomly stepped voltage spikes which modulates 1/f noise property in frequency domain. The appearance of electrical RTN is restricted to limited ranges of bias voltage and temperature. Dependence of RTN statistics on temperature suggests that the dynamic resistance fluctuations could be generally described by a thermal activation model. The extracted activation energy, EA, is found to be 0.3×10−19 J, which is much smaller than reported activation energies for magnetic RTN in early giant magnetoresistive heads.

A comparative study of alternating write-current-induced pole tip protrusion in perpendicular and longitudinal recording heads

This paper presents a comparative study of alternating write-current-induced pole tip protrusions (WPTP) in perpendicular magnetic recording (PMR) and longitudinal magnetic recording (LMR) heads during writing operation. Both finite element modeling and experimental measurements were performed for this study. The results show that the writer resistance and inductance as well as the WPTP of PMR heads are all substantially lower than those of LMR heads within the write-current frequency range under consideration. It is found that the WPTP of a LMR head is mainly attributed to the eddy-current-induced Joule heating in yoke, whereas for a PMR head, the contribution to the WPTP from the Joule heating generated in write coils is comparable to that induced in yoke.

Micromagnetic Study of Short and Long Yoke PMR Head With Trailing Shield

The response of a trailing shielded perpendicular magnetic recording (PMR) write head with a three-turn two-layer coils is calculated using a full micromagnetic large scale model including return pole and soft underlayer. We study the effect of PMR yoke length and write current overshoot on the dynamic response of the head at high frequency. In particular, recording performance parameter, nonlinear transition shift (NLTS) is simulated using micromagnetic media model. Shorter yoke length head improves NLTS as compared with longer yoke length. Measured NLTS has qualitative agreement with micromagnetic model results.

High Precision Erase Band Measurement With Four Written Tracks

This article introduces a four track erase band width (EBW) measurement derived from triple track test. The method writes the first center track to adaptively control the track pitch (TP) and the final center track to minimize the impact from systems positioning error during EBW measurement. It uses one-way dual-frequency scan on the neighboring magnetic write width (MWW) edges to further minimize the impact from systems positioning error. Experiment shows that measured EBW decreases with TP decreasing due to the side reading, cross-track field interaction, and edge noise suppression in perpendicular recording. Setting TP at 100% MWW is proposed for measuring “intrinsic” erase band (EB). The new method demonstrates significant improvement on test accuracy over the conventional methods, and can control EBW measurement variation range within 1 nm. With the new method, the relations of EBW with write revolutions, write current, write frequency, and adjacent track interference (ATI) were experimented and analyzed. The experiment result further validates the new method.

Effects of pinning defects on current-perpendicular-to-plane magnetic recording heads

Effects of pining defects (PDs) on performance of magnetic recording reader are studied micromagnetically. The pinning defects could be present in antiferromagnet (AFM) and synthetic AFM. Presence of pinning defects results in nonuniform pinned layer rotation at parallel (P) state as well as transfer curve (TC) artifacts at antiparallel (AP) state. The high field property, especially rolling off of TC in AP state, is also associated with different types of pinning defects. Time domain baseline popping noise as a result of PDs has been captured in thermal Landau–Lifshitz–Gilbert simulation, which is caused by switching of local magnetic states as a result of either AP pinning spot or P exchange coupling spots with certain dispersion.

Off-Transition Noise Characterization During Head Thermal Protrusion

This paper characterizes the read-back off-transition noise (OTN) in spectral, spatial, and time domains during the thermal protrusion of a magnetic head. In perpendicular recording, the OTN is typically lower than the background noise, and shows bathtub-like cross-track profile. The spatial and spectral characteristics of the read-back OTN make it sensitive to the head positing change in cross-track, down-tack, and vertical directions. In contrast to the conventional on-transition signal reading, the OTN monitoring reverses the usage of signal and noise and lowers the requirement on signal quality. Monitoring OTN during heads thermal control can detect air bearings stability, heads fly-ability, and head-lube/disk contact without Fourier transform (FT) related techniques. A single-track and single read-frequency head-lube/disk contact detection method with high simplicity, high sensitivity, and high repeatability is introduced.