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MA: Fachverband Magnetismus
MA 49: Spin-dependent Transport/ Spin Torque
MA 49.8: Talk
Thursday, March 17, 2011, 12:30–12:45, HSZ 04
Low spin current-driven dynamic excitations and metastability in spin-valve nanocontacts with unpinned artificial antiferromagnet — •Moritz Eggeling1, Theodoros Dimopoulos1, Thomas Uhrmann1, Ole Bethge2, Rudolf Heer1, Volker Hoeink1, and Hubert Brueckl1 — 1Austrian Institute of Technologie GmbH - Devision Nano Systems, Donau-City-Str. 1, 1220 Vienna, Austria — 2Institute for Solid State Electronics, Vienna University of Technology, Floragasse 7, 1040 Vienna, Austria
This work concerns the dynamic excitation of non-uniform, vortex-like magnetic states due to spin-transfer torque in spin-valve nanocontacts, employing an unpinned artificial antiferromagnet of CoFe/Ru/CoFe as polarizer and amorphous CoFeB as free layer. The frequency spectra are in the sub-gigahertz regime for circular contacts of 150 to 200 nm in diameter. The critical current density, marking the onset of the dynamic excitation, attains considerably low values, while the dynamic spectra show reversibility with respect to the DC current. The oscillation power strongly depends on the in-plane magnetic field, assuming maximum values in the vicinity of the free layer's magnetization switching. The maximum in power is accompanied by a minimum in the oscillation linewidth. We also show that for specific current and magnetic field windows metastable dynamic states are excited, believed to induce linewidth broadening.