Michael L. Mallary

Effective field gradient dependence on write field rise time

An analytic expression has been obtained for the field gradient of a recording head at the moment that the write process is completed. Although the head gap is assumed to be much less than the fly height, expressions for the effective spacing of wide gap heads extend the results. From this analysis, it is found that the maximum normalized write field gradient can be obtained, by increasing the write field strength, to partially compensate for poor rise time.

Switching field time dependence of thin film media

The dependence of remanent coercivity of thin film media on pulse duration has been measured for time intervals from 1.4 ns to 270 hr. The apparatus combines the field from a microconductor with that of a DC magnet to switch the media. The data from 53 /spl mu/s to 270 hr fits well to Sharrocks Law with an exponent of 0.716. The data for times less than 8 ns indicate weak gyro-magnetic enhancement of the switching field. Micromagnetic simulation shows that this can be explained by either magnetostatic or exchange coupling between the grains.

Advanced multi-via heads

Advanced versions of thin film recording heads with multiple magnetic vias are reported on. In these designs the flux path makes more than one pass through a multilevel race track coil. The multiple flux paths multiply the number of effective turns in the head. With this patented approach called the Diamond Architecture low inductance and resistance is achieved with a large number of effective turns. Advanced designs based on three layer coil, laminated yokes and four yoke turns are described. Frequency response data on the heads with laminated yokes show clear improvement over unlaminated heads. >

Two dimensional model of eddy currents and saturation in thin film write heads

A two-dimensional model of an MR write head has been constructed using a finite element model. The model includes the eddy currents as well as nonlinear saturation of recording head material. The recording head field (deep gap field) was calculated as a function of write-current frequency and amplitude for two recording-head materials, standard 80/20 NiFe and high saturation magnetization Ms material 50/50 NiFe. The analysis was also done in the time domain and was compared with experimental data on field response, using both a microloop apparatus and impedance measurements. Fair agreement was obtained between the model and the data. The deep gap field has a time delay relative to the write current, which varies as a function of current frequency and amplitude.

Signal to noise comparison between GMR and spin tunneling sensors

Starting from these fundamental equations for these noise sources, scaling relationships for the signal to noise ratios of these devices have been derived. From these relationships it is clear that spin tunneling devices will need major improvements b e f m there is any hope of breaking even with GMR sensors. It is also clear that as the dimensions of recording systems are scaled down the spin tunneling conductance per unit area must increase as the inverse square of the scaling factor in order to maintain the same standing relative to GMR.