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High Speed Switching in Magnetic Recording Thin-Film Heads
Thesis or dissertation
University of Exeter
There has always been an increasing demand for high density data storage. However, the increased areal storage densities of hard disk drives require a level of miniturisation of the recording heads where the micromagnetic details and switching mechanisms can no longer be ignored. Furthermore, theoretical and numerical studies on thin-film recording heads tend to separate the micromagnetics from the electromagnetic aspects of the head during switching and hence ignore the lossy nature of head materials. This project was aimed to develop a numerical simulation approach that simultaneously incorporates the fundamental micromagnetic and electromagnetic details of magnetic materials to study the fast switching process in soft magnetic materials in general, and in thin-film inductive writers in particular. The project also was aimed at establishing an impedance measurement system to characterise losses in magnetic recording heads, and to allow comparison with the simulations. This project successfully met all its original objectives. A numerical technique to simulate the dynamic behaviour of magnetic materials and devices has been developed, and applied to study the switching process in thin-film recording heads. Two-dimensional simulations of complete commercial head structures including the coils and pole regions were carried out and parameters such as gap field rise times, gap field distributions, and core inductances, which are important for head designers, were predicted. Moreover, the role of eddy currents delaying the magnetisation switching was elucidated. Furthermore, it was found that the gradient of the recording fields were sharper near the conrner regions of the poles when considering magnetic details. A high precision, high bandwidth impedance measurement system was established to characterise losses in magnetic heads. Fittings of measured core inductances to a proposed equivalent circuit model of the core’s relaxation processes revealed the switching times of heads (of the order 0.1 to 1.0ns).
Aziz, Mustafa M.
PhD in Engineering