Klaas Berend Klaassen

Nonlinear, eddy current damped, thin-film write head model

A new thin-film write head model is described which is based on electrical impedance versus frequency measurements. The model includes the effects of head saturation and eddy current damping making it useful for simulation of the electrical input port (head coil) and magnetic output port (pole tip) signals, which would be observed under actual write conditions.

Extra-low-frequency noise in giant magnetoresistance recording heads

Extra-low-frequency (ELF) noise was studied in flyable, shielded giant magnetoresistance heads using a novel, ultralow-noise amplification system. The noise power spectral density had a 1/f character over wide frequency and sense current ranges. The noise was mainly magnetic in origin. It, however, did not follow Hooge’s formula. Random telegraph noise (RTN) was observed after moderate current stressing. The characteristic dwell times of the two-level RTN switching changed with applied field, sense current, and temperature. We consider the ELF noise as a sensitive diagnostic tool, since deviations from the 1/f dependence signal the existence of undesirable magnetic states.

Correlation of DC noise and transition noise in magnetic recording

We studied a correlation between the local transition noise and the dc noise at the same location of magnetic medium. We describe experimental techniques for local dc noise and transition noise analysis and demonstrate that the local fluctuations of the dc saturated magnetization become enhanced when a transition is written at this location. This enhanced local dc noise is a very significant contributor to the total noise power of a transition.

Writing and reading at high data rates

This paper describes the analysis of an MR read/write channel for high data rate magnetic recording. Using current, industrially available components, characterized to frequencies >1 GHz, data rate limiting factors such as bandwidth, write current overshoot, inadequate write field swing, write field rise time and excessive write field zero-crossing shift are investigated. From this, conclusions can be drawn about the maximum attainable data rate (in casu 16 MB/s). For the components used in this study, the eddy current damping in the yoke of the inductive write head turned out to be the major restriction in achieving higher data rates.

The spatial structure of media noise

The spatial structure of dc and transition noise in perpendicular and longitudinal recording media is studied. Experimental techniques for local dc noise and transition noise analysis are described. It is demonstrated that the dc and transition noise is deterministic and repeatable at given medium location. The transition noise is correlated with the dc noise; the local fluctuations of the dc saturated magnetization are becoming enhanced when a transition is written at this location. This enhanced local dc noise is explained by local medium demagnetization which is strongest at the transition, it determines the transition noise magnitude.

A resonant switching write driver for magnetic recording

This paper describes a high-speed circuit for driving magnetic recording write heads. Resonant current switching enables a reduction in power consumption without compromising switching speed. With a 100 nH load and 120 mA/sub pp/ write currents, a rise time of 1.6 ns was achieved with a 7 V power supply.