Spin tunnel junctions with tunneling magnetoresistance of $\text{36.5\%±0.5\%,}$ resistance-area product of $\text{35±6\hspace{0.17em}}{\mathrm{k\Omega \times \mu m}}^{\mathrm{2}},$ and junction area between 6 and $\text{75\hspace{0.5em}}{\mathrm{\mu m}}^2$ were fabricated. The barrier height is $\text{2.5±0.3\hspace{0.17em}}\mathrm{eV}$ and the barrier thickness is $\text{7.7±0.3\hspace{0.17em}Å.}$ Large tunneling magnetoresistance (TMR) values are obtained by vacuum anneal (at temperatures from 100 to 240 °C for over 5 h) of junctions prepared with as-deposited TMR of $\text{21\%±1.7\%,}$ and an as-deposited resistance-area product of $\text{25±6\hspace{0.17em}}{\mathrm{k\Omega \times \mu m}}^{\mathrm{2}}.$ Two regimes occur during anneal. The first one occurs for anneals up to 200 °C where TMR and junction resistance increase, but the barrier parameters are unaltered. The second occurs above 200 °C, where TMR increases faster, together with an increase in barrier height. At 240 °C, TMR starts to decrease. Rutherford backscattering analysis indicates an asymmetry in the oxygen distribution in the as-deposited barrier. The oxygen distribution becomes homogeneous for anneals above 150 °C.

We evidence multiple coherent precessional magnetization reversal in microscopic spin valves. Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ. At high fields a phase coherent reversal is found revealing periodic transitions from switching to nonswitching under variation of pulse parameters. At the low field limit the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold.

We demonstrate a quasiballistic switching of the magnetization in a microscopic magnetoresistive memory cell. By means of time resolved magnetotransport, we follow the large angle precession of the free layer magnetization of a spin valve cell upon application of transverse magnetic field pulses. Stopping the field pulse after a $180°$ precession rotation leads to magnetization reversal with reversal times as short as 165 ps. This switching mode represents the fundamental ultrafast limit of field induced magnetization reversal.

An asymmetry in the interfacial anisotropies of Pt/Co and Co/Pt interfaces was observed in Pt/Co/Pt sputtered trilayers, the interfacial anisotropy arising from the bottom Pt/Co interface being significantly higher than that from the top Co/Pt one. Interdiffusion at the top interface is believed to be the main factor for this asymmetry. It dramatically decreases the anisotropy of the stack when the cobalt layer is thinner than 1 nm. By introducing ultrathin layers of materials immiscible with Co and acting as a diffusion barrier at the Co/Pt interface, the effective anisotropy can be doubled in this low Co thickness range. This is of great interest for spintronic devices, particularly for out-of-plane magnetized magnetoresistive random access memory structures that require high perpendicular magnetic anisotropy when their lateral dimensions are reduced below 45 nm.

A new approach to increase the downsize scalability of perpendicular STT-MRAM is presented.