Magnetoresistance and electrical conductivity of manganite bicrystal contacts

Magnetic bicrystal contacts in epitaxial films of manganite La_0.67Ca_0.33MnO₃ prepared on bicrystal substrates with a misorientation of the NdGaO₃(110) basal planes rotated through an angle of ±14° around the bicrystal boundary line were studied. The temperature dependence of the contact electrical resistance was studied, and the magnetoresistance was measured in fields of up to 1.5 kOe. It is shown that the suppression of ferromagnetic correlations near the boundary leads to the formation of a layer having a substantially lower Curie temperature. Magnetoresistance of 150%, which is record-braking for bicrystal contacts, was measured at T = 4.2 K in a weak magnetic field of about 500 Oe and at a characteristic electrical resistance of the boundary of 3 × 10⁻⁶ Ω cm². It is found that slight orthorhombic distortions of a La_0.67Ca_0.33MnO₃ film due to a lattice mismatch with the NdGaO₃(110) substrate crystal structure lead to the formation of biaxial magnetic anisotropy in the La_0.67Ca_0.33MnO₃ film.