Wei Yu





Magnetization dynamics of nanoscale magnetic and spintronic  materials



Time resolved scanning Kerr microscopy (TRSKM) measurements will be used to study magnetization dynamics in two different geometries.  In the first part measurements will be performed on partly built hard disk writer structures supplied by Seagate Technology.  The writer focuses and amplifies the flux from a thin film yoke structure within a pole piece of nanoscale width.  However the underlying magnetization processes are poorly understood and the methods required to optimize the rise time of the write field at the recording medium are unknown.  By acquiring time resolved images of the magnetization within the structure understanding of writer operation will be greatly advanced. In the second part, Spin Transfer Torque (STT) in non-local transport geometries will be studied. When an electrical current is passed from one ferromagnet to another, there is a transfer of angular momentum that causes a torque (STT) to be exerted upon the magnetic moment of each layer.  The STT can be used to switch the direction of the magnetic moment, or send it into a state of continuous oscillation known as precession that leads to the emission of microwaves.  Both of these phenomena involve motion on timescales of less than 1 nanosecond. The STT was initially observed in multilayered nano-pillar samples, but has recently been shown to also operate in a lateral "non-local" geometry that provides greater flexibility in the construction of spintronic circuits.  A spectrum analyzer will be used to detect steady state spin transfer induced precession at frequencies of up to 50 GHz, while a pulse generator and sampling oscilloscope will be used to study the approach to the steady state. TRMOKE will be used to resolve the dynamics of the vector magnetization. There may also be opportunity to participate in time resolved x-ray photoemission microscopy experiments performed on either type of sample at the Diamond Light Source