L.F.D. Pereira

Characterization of CoFeB electrodes for tunnel junctions

This paper compares structural and magnetic properties of CoFeB thin films and tunnel junction electrodes, with a boron content of 10 at % (CFB10) and 20 at % (CFB20). X-ray diffraction of 20–60 A thick CoFeB films indicates amorphous structure in the as-deposited state, independent of the B content. The CFB10 films develop a strong (111) texture after annealing at 280 °C, while CFB20 films require annealing at 320 °C. However, films with either composition can remain amorphous upon anneal, if thinner than 40 A. The crystallization temperature was corroborated by analysis of exchange bias and coercive fields. Tunnel junctions based on CFB10 and CFB20 were fabricated by ion beam and magnetron sputtering, respectively, and patterned down to 1×2μm2. From magnetic measurements, bottom-pinned MnIr∕CFB10 or MnIr∕CFB20 junctions have similar exchange fields upon anneal. For top-pinned structures, week exchange is obtained using CFB20∕MnIr. Synthetic antiferromagnets (CFB∕Ru∕CFB) were also studied. Antiferromagne...

Magnetic hyperfine field in antiferromagnetic RGa2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) studied by perturbed angular correlation spectroscopy using Cd111

The magnetic and electric hyperfine interactions of the nuclear probe Cd111 in the hexagonal antiferromagnetic rare earth-gallium RGa2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) intermetallic compounds have been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature. With the exception of R = Nd and Ho, the magnetic hyperfine field Bhf is roughly proportional to the spin projection (g − 1)J of the R constituent. However, in the group of the light rare earths, the variation of Bhf with (g − 1)J is much weaker than that for the heavy R constituents, in contrast to the trend reported for all rare earth intermetallics investigated up to now as well as to the trend of the magnetic ordering temperatures of RGa2. The orientation of the 4f spins relative to the c axis of RGa2 deduced from the angle between Bhf and the symmetry axis of the electric field gradient was found to be temperature independent and in agreement with the results of previous magnetization measurements...