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CoFeB/MgO-based perpendicular magnetic tunnel junctions (p-MTJ's) with high anisotropy and low damping are critical for spin-torque transfer random access memory (STT-RAM). Most schemes of making the pinned CoFeB fully perpendicular require ferrimagnets with high damping constants, a high temperature-grown L1 0 alloy, or an overly complex multilayered synthetic antiferromagnet (SyAF). We report a compositional study of perpendicular Co x Pd alloy-pinned Co 20 Fe 60 B 20 /MgO based MTJ stacks, grown at moderate temperatures in a planetary deposition system. The perpendicular anisotropy of the Co x Pd alloy films can be tuned based on the layer thickness and composition. The films were characterized by alternating gradient magnetometry (AGM), energy-dispersive X-rays (EDX), and X-ray diffraction (XRD). Current-in-plane tunneling (CIPT) measurements have also been performed on the compositionally varied Co x Pd MTJ stacks. The Co x Pd alloy becomes fully perpendicular at approximately x = 30% (atomic fraction) Co. Full-film MTJ stacks of Si / SiO 2 / MgO (13) / Co X Pd 100-x (50) / Ta (0.3) / CoFeB (1) / MgO (1.6) / CoFeB (1) / Ta (5) / Ru (10), with the numbers enclosed in parentheses being the layer thicknesses in nm, were sputtered onto thermally oxidized silicon substrates and in-situ lamp annealed at 400 o C for 5 minutes. CIPT measurements indicate that the highest TMR is observed for the CoPd composition with the highest perpendicular magnetic anisotropy.

The effects of shape and edges in magnetic elements with reduced dimensions on the magnetization reversal of cross- and framed cross-shaped Ni79Fe21 (30nm) films were studied. Remagnetization details in the stripes of the patterned structures, which had 3 μm to 30 μm widths and ~100 μm lengths, were visualized by the magneto-optical indicator film technique. The magneto-optic images revealed three different types of the domain structure formation and evolution in the samples during their magnetization reversal: (i) spin rotation with growth and annihilation of a cross-tie structure in the stripes perpendicular to the applied field, (ii) nucleation and fast motion of special boundaries, which consist of a number of coupled vortices located along both edges of the stripes parallel to the applied field, and (iii) nonuniform magnetization rotation with macrodomain nucleation and domain wall motion in the large unpatterned part of the films. It was experimentally revealed that there exists a dependence of the critical field for nucleation and motion of domain walls in the parallel-to-field stripes on their width and frame width. In particular, an inverse proportionality between this nucleation field and stripe width was found. Both experimental and simulation results show that, in cases (i) and (ii), the magnetostatic fields, which are formed on the edges of the stripes and at their intersections, play a crucial role in the formation of spin inhomogeneities and switching of the samples.

The thermal stability of C d C o 'bottom' spin valve structures deposited on NiO has been assessed as a function of temperature, time, and cap layer compositions including Au, Ta and Ta,O,. Samples with 5.0 nm thick cap layers of Au showed a reduction in giant magnetoresistance (GMR) from 9.3% to 3.6% after a 0.5 hr anneals at 250 'C. As a function of time, the sample resistance, R (t) , showed an exponential saturation with a time constant, T , which follows an Arrhenius law, 7 = TO exp[AE/kT], with A E = 1.29 f 0.03 eV and TO on the order of lo-' s to lo-' s. These parameteqwhichfit R (t) , correlate with the time and anneal temperature dependence of GMR decay in the Au-capped spin valves. In contrast, samples with Ta or Ta,O, cap layers showed good stability for 0.5 hr anneals up to 325 'C. Decreases in GMR from 12.7% to 3.9% following a 20 h anneal at 325 ' C are accompanied by significant changes in the hysteresis loops which appear to be associated with the pinned layer. With a 5.0 nm Ta cap, R(t) follows a logarithmic-like time dependence characteristic of a distribution of activation energies.