Large magnetotunneling effect at low magnetic fields in micrometer-scale epitaxial La_0.67Sr_0.33MnO₃ tunnel junctions

We have used a self-aligned lithographic process to fabricate magnetic tunnel junctions of La_0.67Sr_0.33MnO₃ down to a few micrometers in size. We have obtained a magnetoresistance ratio as large as 83% at low magnetic fields of a few tens of Oe, which correspond to the coercivities of the magnetic layers. Transmission-electron-microscopy analysis has revealed the heteroepitaxial growth of the trilayer junction structure, La_0.67Sr_0.33MnO₃/SrTiO₃/La_0.67 Sr_0.33MnO₃. We have observed current-voltage characteristics typical of electron tunneling across an insulating barrier. The large magnetoresistance is likely due to the nearly half-metallic electronic structure of the manganites.