Coherent magnetic reversal in half-metallic manganite tunnel junctions

We report coherent magnetization reversal in the ${\mathrm{La}}_{\mathrm{0.7}}{\mathrm{Ca}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}{\mathrm{/NdGaO}}_{\mathrm{3}}{\mathrm{/La}}_{\mathrm{0.7}}{\mathrm{Ca}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}$ tunnel junctions probed by spin-polarized tunneling. The junction resistance shows an extremely sharp switching with distinct binary resistances and its two-dimensional angular dependence reveals two different magnetic anisotropies in play in the top and bottom ${\mathrm{La}}_{\mathrm{0.7}}{\mathrm{Ca}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}$ electrodes. The large bottom electrode $\text{(50×2000\hspace{0.05em}μ}\mathrm{m})$ shows the effective twofold crystalline anisotropy and the top electrode $\text{(6×6\hspace{0.05em}μ}\mathrm{m})$ shows an additional fourfold anisotropy. The geometrical expression of the switching fields in two-dimensional polar coordinates provides evidence that the coherent magnetization reversal of the junctions, particularly the top electrode, closely resembles the ideal coherent rotation model.