Coherent magnetic reversal in half-metallic manganite tunnel junctions

We report coherent magnetization reversal in the La0.7Ca0.3MnO3/NdGaO3/La0. 7Ca0.3MnO3 tunnel junctions probed by spin-polarized tunneling. The junctio n resistance shows an extremely sharp switching with distinct binary resist ances and its two-dimensional angular dependence reveals two different magn etic anisotropies in play in the top and bottom La0.7Ca0.3MnO3 electrodes. The large bottom electrode (50x2000 mum) shows the effective twofold crysta lline anisotropy and the top electrode (6x6 mum) shows an additional fourfo ld anisotropy. The geometrical expression of the switching fields in two-di mensional polar coordinates provides evidence that the coherent magnetizati on reversal of the junctions, particularly the top electrode, closely resem bles the ideal coherent rotation model. (C) 2000 American Institute of Phys ics. [S0003- 6951(00)02649-8].