Electrical detection of the antiferromagnetic transition in MnTiO₃ ultrathin films by spin Hall magnetoresistance

We have studied the spin Hall magnetoresistance (SMR) arising at the interface of Pt and antiferromagnetic insulator MnTiO₃ thin films. Using c axis oriented single-crystalline ilmenite-type MnTiO₃ films on Al₂O₃ (0001) substrates grown by pulsed-laser deposition, we fabricated L-shaped multi-terminal Pt/MnTiO₃ devices in which the longitudinal resistances of two orthogonally arranged channels can be simultaneously measured by the four-probe method. Magnetic field angular dependence of the magnetoresistance was consistent with symmetry relations for the SMR between spin-current polarization in Pt and magnetic moment in MnTiO₃, evidencing the predominant SMR contribution. By utilizing distinct SMR responses of the two channels when a magnetic field was applied in parallel to one of the channels, we determined the Néel temperature (T_N) to be 63 K in a 20-nm-thick MnTiO₃ film, comparable to T_N of a 40-nm-thick MnTiO₃ film separately measured with a superconducting quantum interference device magnetometer. The electrically determined T_N persisted down to the film thickness of 2.9 nm, indicating the robust antiferromagnetic ordering even at the surface of MnTiO₃ ultrathin films.