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Abstract
The use of magnetoresistive playback technology in high density magnetic recording systems poses special challenges for the hard drive designer. The MR sensor is an intrinsically nonlinear device which must be biased into a region of linear response with respect to the external field. Additional magnetic structures are required to stabilize the sensor against domain formation. These structures result in complicated magnetization processes during the playback of recorded information. The spatial variation of the MR head replay voltage is complicated and has asymmetries due to the magnetic structure of the device. These issues require sophisticated modeling to properly characterize the system performance.
This dissertation presents studies of several key problems involved with integrating MR heads into hard disk drives. Models of varying levels of sophistication have been developed for this work. These range from simple linear reciprocity analyses to large scale numerical energy minimization techniques. The spatial variation of the MR playback voltage is studied as a function of the system geometry using a linear theory. The response is found to depend strongly on both the head and medium parameters. Instabilities are investigated using a large scale numerical model for a particular head fabrication geometry. The interface between the stabilizing magnetic structures and the head material produces repeatable hysteretic effects in the voltage response. The saturation of MR heads is characterized using numerical modeling. This is important for estimates of the error rate in the drive. The results show that the saturation characteristics can vary significantly between different head designs and as a function of the spatial position of the device. The issues involved with the use of MR heads as positioning sensors are also addressed. The servo system stability is a strong function of the recording parameters and the head spatial symmetry. Optimization of the servo system is investigated using the large scale numerical model.
