We report an unconventional oscillatory tunnel magnetoresistance as a function of the applied bias in double barrier magnetic tunnel junctions that were made of two Al 2 O 3 barriers sandwiched by three ferromagnetic layers. When the center ferromagnetic layer is aligned antiparallel to the top and bottom magnetic layers, a distinct magnetoresistance oscillation appears with respect to the increase of the bias voltage at 4.2 K and at room temperature. The period of the oscillation is about 1.6 mV.
We report the observation and micromagnetic analysis of current-driven
magnetization switching in nanoscale ring-shaped magnetic tunnel junctions.
When the electric current density exceeds a critical value of the order of
$6\times 10^{6}$A/cm$^2$, the magnetization of the two magnetic rings can be
switched back and forth between parallel and antiparallel onion states.
Theoretical analysis and micromagnetic simulation show that the dominant
mechanism for the observed current-driven switching is the spin torque rather
than the current-induced circular Oersted field
Perpendicular magnetic tunnel junctions (pMTJs) with tunneling magnetoresistance (TMR) as high as 14.7% at room temperature were fabricated. The continuous film and pMTJs with Co/Pt multilayer magnetic electrodes and AlOx tunnel barrier were annealed at different temperatures and the effect of annealing on their properties was investigated. The hysteresis loops and X-ray reflectivity measurement show that the interdiffusion of Co and Pt atoms is slight when annealed below 523 K. However, the patterned magnetic tunnel junction gets TMR ratio from 12.3% to the maximum value of 14.7% after annealing at 483 K for 1 h.
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