Dimitri Houssameddine

Spin transfer induced coherent microwave emission with large power from nanoscale MgO tunnel junctions

In low resistance-area product MgO magnetic tunnel junction nanopillars, we observe high integrated power (up to 43nW), narrow linewidth (down to 10MHz), spin transfer induced microwave emission at frequencies up to 14GHz due to precession of the free layer magnetization at room temperature. Although all devices were fabricated on the same wafer, they present bimodal transport and precessional characteristics. The devices in which the narrowest linewidths were observed exhibited low resistance and tunneling magnetoresistance (30%), while maintaining large integrated power.

Amplitude and phase noise of magnetic tunnel junction oscillators

The microwave emission linewidth of spin transfer torque nano-oscillators is closely related to their phase and amplitude noise that can be extracted from the magnetoresistive voltage signal V(t) using single shot time domain techniques. Here we report on phase and amplitude noise studies for MgO based magnetic tunnel junction oscillators. The analysis of the power spectral densities allows one to separate the linear and nonlinear contributions to the phase noise, the nonlinear contribution being due to the coupling between phase and amplitude. The coupling strength as well as the amplitude relaxation rate can be directly extracted.

100 ps precessional spin-transfer switching of a planar magnetic random access memory cell with perpendicular spin polarizer

Ultrafast spin-transfer precessional switching between two stable states of a magnetic random access memory device is demonstrated in structures comprising a perpendicularly magnetized polarizing layer (PL⊥), an in-plane magnetized free layer (FL), and an in-plane magnetized analyzing layer (AL) in a PL⊥/spacer/FL/spacer/AL stack. Back and forth switching can be achieved with sub-ns current pulses of the same polarity. The spin-torque influence from the analyzer leads to an asymmetric dependence of the switching properties as a function of the current sign and initial state.

Spin torque driven excitations in a synthetic antiferromagnet

Spin polarized current induced self oscillations have been investigated in both the free layer and the synthetic antiferromagnetic (SAF) pinned layer of spin valve nanopillars. Compared with free layer excitations, the acoustic type SAF excitations are characterized by high emitted power and much narrower linewidth. Furthermore, in contrast to free layer excitations, the SAF in-plane precession mode exhibits an unexpected crossover from redshift (df/dI 0) in frequency f versus current I as the in-plane magnetic field is increased. From simulations we identify this crossover as a signature of large amplitude spin current induced precessional dynamics in the SAF.