Current-driven domain wall depinning and resonance in notched Permalloy nanowires

Christopher Marrows 1Serban Lepadatu 1Mark Hickey 1Antoine Vanhaverbeke 2Ola Wessely 3Alessandro Potenza 4Helder Marchetto 4Timothy Charlton 5Del Atkinson 6Sarnjeet S. Dhesi 4Sean Langridge 5David Edwards 3Rolf Allenspach 2

1. University of Leeds (UOL), Woodhouse Lane, Leeds ls2-9jt, United Kingdom
2. IBM Research GmbH, Zurich Research Laboratory, Saeumerstrasse 4, Zürich CH-8803, Switzerland
3. Imperial College London, South Kensington, London SW72AZ, United Kingdom
4. Diamond Light Source (DIAMOND), Didcot OX110DE, United Kingdom
5. Science and technology facilities council, Rutherford Appleton laboratory, Didcot OX110QX, United Kingdom
6. Department of Physics University of Durham, Durham DH13LE, United Kingdom

Abstract

Current-driven domain wall motion not only offers fascinating basic physics but offers the prospect of storage-class non-volatile solid state memories. The fruitfly sample used in experimental studies to date is the lithographically patterned permalloy nanowire. Here we describe our recent work on such structures, with patterned pinning centres, notches, halfway along their length. Our key techniques have been high-resolution magnetic imaging by XMCD PEEM and SEMPA, as well as magnetotransport measurements. We have measured the spin polarisation of the current (P~0.4) and the degree of non-adiabaticity of the spin torque (beta~0.04) in Permalloy by studying the depinning boundary of the DWs pinned in triangular notches. We have demonstrated that the depinning current at zero field may be engineered by controlling the half-angle of the triangular notch, which varies the restoring force the pinning centre applies to the wall as it attempts to leave. We have also excited pinned walls with RF currents: in a triangular notch the behaviour is highly anharmonic, whilst a well-defined eigenfrequency is found for parabolic notches, which provide an almost harmonic pinning potential.

 

This work was supported by the ESF (SpinCurrent consortium), the EPSRC (Spin@RT Consortium), and Diamond Light Source.

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Presentation: Invited oral at E-MRS Fall Meeting 2009, Symposium E, by Christopher Marrows
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-15 16:48
Revised:   2009-08-13 17:33
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