Electron transport in manganite bicrystal junctions

The transport and magnetic properties of junctions created in La$_{0.67}$Sr$_{0.33}$MnO$_3$ thin films epitaxially grown on substrates with a bicrystal boundary have been investigated. In tilted neodymium gallate bicrystal substrates, the NdGaO$_3$(110) planes are inclined at angles of 12$^\circ$ and 38$^\circ$. The temperature dependences of the electrical resistance, magnetoresistance, and differential conductance of the junctions at different voltages have been measured and analyzed. It has been found that the magnetoresistance and electrical resistance of the junction significantly increase with an increase in the misorientation angle, even though the misorientation of the easy magnetization axes remains nearly unchanged. The ratio of the spin-dependent and spin-independent contributions to the conductance of the bicrystal junction increases by almost an order of magnitude with an increase in the misorientation angle from 12$^\circ$ to 38$^\circ$. The magnetoresistance of the junction increases with decreasing temperature, which is most likely associated with an increase of the magnetic polarization of the electrons. It has been shown that, at low (liquid-helium) temperatures, the conductance depends on the voltage $V$ according to the law $V^{1/2}$, which indicates the dominant contribution from the electron-electron interaction to the electrical resistance of the junction. An increase in the temperature leads to a decrease in this contribution and an increase in the contribution proportional to $V^{3/2}$, which is characteristic of the mechanism involving inelastic spin scattering by surface antiferromagnetic magnons.