Extending our knowledge of how magnetic materials behave on an atomic scale has led to considerable technological advances, particularly in the area of information storage. Scientists have been using the Nanoscience beamline at Diamond to study the properties of magnetic domain walls, the boundary between areas of material with uniform magnetization. The group has modeled the way that these walls move when current is applied, a technique which has promising applications in writing data in more efficient digital memory devices, as well as improving our fundamental understanding of magnetism. This work has been published in the journal Physical Review B.
Scientists from the University of Leeds have been using the PhotoEmission Electron Microscope (PEEM) on the Nanoscience beamline I06 to image the structure of magnetic domain walls in a notched permalloy wire. The domain walls are trapped at the pinning potential provided by the notch. The presence or absence of a wall in a such a notch can be used to represent a bit of digital data. The variation of critical current density with magnetic field was measured using pulsed current measurements to give an experimental depinning boundary which could then be compared to micromagnetic simulations.
The micromagnetic structure can be very complex, but the data obtained through the PEEM imaging provides enough information to build up detailed models and predict the behaviour of these nanostructures. This crucial to exploiting the structures in technological applications.
"In this experiment we were able to separate and understand the two different ways that a spin-polarized current can depin a domain wall in order to start it moving. We will now exploit this understanding to reduce the size of the current pulse needed, to make a device that requires less energy to operate. We’re currently planning more experiments with the scientists at Diamond to watch the wall moving using the microscope at I06."
Chris Marrows, University of Leeds
Notched Permalloy Wire
Experimental determination of spin-transfer torque nonadiabaticity parameter and spin polarization in permalloy, S. Lepadatu, M.C. Hickey, A. Potenza, H. Marchetto, T.R. Charlton, S. Langridge, S.S. Dhesi, C.H. Marrows, Physical Review B (2009)
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