Bloch Line Mobility of ≃ 48,000 cm/Oe-sec, Automatic Wall Placement, and some Dynamic Properties of Crossties

Abstract

Progress toward a thin film serial access memory using crossties and their absence to represent digital information is reported. The data rate is dependent on Bloch line velocity. Using a Permalloy film 370 Å thick the Bloch line mobility (μ) was found to be approximately 48,000 cm/Oe‐sec with a coercive force of 0.38 Oe. The velocity appears to follow the equation $\mathrm{v}\mathrm{\hspace{0.17em}=\hspace{0.17em}\mu (}\mathrm{H}\mathrm{\hspace{0.17em}-\hspace{0.17em}}{\mathrm{H}}_{\mathrm{c}})$ with H as large as 5 Oe. The mobility was measured by applying a 550 nsec pulse 0.76 Oe in amplitude along the hard axis of the film. The Bloch line moved 100 μm. Other techniques were also employed to measure Bloch line velocity. These experiments were performed on films deposited in the presence of a nonuniform magnetic field which produced a periodic spatial variation in the easy axis of the film. After the application of a uniform magnetic field > H_K along the average hard direction, the walls automatically appeared in the desired locations.