MEASUREMENTS OF SPIN TORQUES DUE TO REORIENTABLE ANOMALOUS HALL SPIN CURRENTS
This dissertation discusses spin currents generated by the anomalous Hall effect in ferromagnetic materials. It primarily presents second harmonic Hall technique measurements with an in-plane magnetic sensor layer that demonstrate that the spin polarization of such spin currents orients itself parallel to the magnetization of the generating layer. Hence the work demonstrates that one can control the spin polarization of spin currents generated in this way, such that torques may be actively reoriented during measurement by controlling the magnetization of the generating layer. By these measurements, this work also estimates the spin torque efficiency of the alloy of iron and gadolinium used for this measurement to be about 1%. This dissertation then discusses ongoing measurements using the spin torque ferromagnetic resonance technique modified by application of a DC bias current to characterize the size of the anomalous Hall spin torque efficiency in a cobalt holmium alloy and several other materials. The author presents related ongoing efforts with additional experimental techniques to understand and utilize the anomalous Hall spin current effectively. This work also discusses practical applications for reorientable spin torques.
Applied physics; Condensed matter physics; Materials Science; Anomalous Hall Effect; MRAM; Spin; Spin Torque; Spin Hall Effect; Spintronics
Ralph, Daniel C.
Buhrman, Robert A.; Kim, Eun-Ah
Ph. D., Physics
Doctor of Philosophy
dissertation or thesis