Microscopic and macroscopic spin transport phenomena

• Main Author: Murphy, Benedict Andrew
• Other Authors: O'Grady, Kevin ; Hirohata, Atsufumi
• Published: University of York 2016
• Subjects: 621.381
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702664

Spintronics is the field concerned with the control of electron spin. In logic devices electron charge is manipulated, in computer data storage the magnetisation of a domain is altered; spintronics offers a hybrid between the two. This could be exploited in non-volatile random access memory cells for low power data storage. All-metal Lateral spin-valve devices were fabricated by electron beam lithography to investigate spin transport phenomena. The fabrication and measurement processes were optimised and lateral spin-valve devices were successfully fabricated with spin diffusion lengths of (200±25) nm and (310±30) nm in 100 nm and 200 nm wide Copper wires respectively. Spin filtering was previously observed by patterning nano-scale wires to be laterally asymmetric. Here, nano-scale wires were patterned to have a laterally symmetric spin diffusion path. No increase in signal due to the filtering effect was observed, thus confirming the phenomenological model put forward. Also, the spin diffusion path in a lateral spin valve was split into a ring geometry. By applying a field gradient across the ring, the operational efficiency was improved by 30%. The observation of a mechanically induced spin current has been achieved for the first time. The design of an optical measurement system that rotates a sample at up to 200~Hz is presented here. Deviation in the moment on the surface of a paramagnetic Tungsten foil from the moment induced by the Barnett effect confirms that a spin current may be induced by mechanical rotation. In summary, design and development of magneto-electrical and mechano-optical measurement systems has been achieved. The improvement in the operational efficiency in lateral spin-valves could be used alongside materials such as Heusler alloys to provide cheaper efficient logic devices. The observation of a mechanically induced spin current in Tungsten precedes the future study of the effect in other paramagnetic materials, such as Platinum or Palladium.