SPIN-WAVE DOPPLER TECHNIQUE FOR MEASURING SPIN CURRENT POLARIZATION
Konrad Hsu Aschenbach1,2, R. D. McMichael1
1 Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899
2 Maryland NanoCenter, University of Maryland, College Park, MD 20742
Current flowing in magnetic metals is polarized: up-spins and down-spins carry a different portion of the current. As a consequence, there is a flow of magnetization associated with any electrical current. We measure the velocity of the magnetization flow using the Doppler shift of spin waves  propagating with and against the flow. A key parameter we obtain from this measurement is the current polarization P.
The success of MRAM and other new spintronic future electronic will require new materials with high current polarization. While precise measurement of P has been historically plagued by interface effects, the novel spin-wave Doppler effect overcomes these limitations via a non-contact radio-frequency approach.
Our laboratory has already demonstrated the technique on varied ferromagnetic alloys such as Ni80Fe20 , CoFeG , and PyGd . Our current objective is to improve the performance of the technique to quantify P in CoFeB and the Heusler alloys (i.e., Co2MnSi, Co2MnGe), samples of which will be provided by collaborators and prepared using ion milling. Out of these promising categories, we aim to shed light on which alloys are most likely to fuel the success of future spin-based electronics.
This work has been supported in part by the NIST-CNST/UMD-NanoCenter Cooperative Agreement.
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