Effects of Cobalt-Permalloy Cosputtering in a Nanowire Structure on Magnetic Fluctuation and Auto-Oscillation

A magnetic nanostructure for auto-oscillation, induced by spin-transfer torque, is fabricated by cosputtering permalloy with cobalt. Although the system does not meet the critical size and current requirements for direct auto-oscillation, magnetic signals resulting from spin wave excitation and magnetic fluctuations are measured by a Brillouin light scattering (BLS) system. From the analysis of the BLS spectrum, the threshold current for auto-oscillation is estimated to be 27.3% lower in Py1-xCox (x = 0.2095) than in Py1-xCox (x = 0.0). It is surmised that the cobalt in permalloy improves the efficiency of transferring spin toque for auto-oscillation.