Metallic conduction and ferromagnetism in MAl2O4/SrTiO3 spinel/perovskite heterostructures (M = Fe, Co, Ni)

Recently, a high mobility quasi-two-dimensional electron gas has been reported for the heterointerface between two insulating and nonmagnetic oxides of spinel gamma-Al2O3 and perovskite SrTiO3 (STO). Herein, we fabricated the epitaxial heterostructure with Al-based magnetic spinel oxide MAl2O4 (M = Fe, Co, Ni) on perovskite STO. Remarkably, all the MAl2O4 (M = Fe, Co, Ni) films exhibit ferromagnetic behavior up to room temperature. Although FeAl2O4/STO is insulating, the NiAl2O4/STO and CoAl2O4/STO heterointerfaces are found to be highly metallic and exhibit the anomalous Hall effect (AHE) at temperatures below 30 K. Their Hall mobility is as high as 3 x 10(-4) cm(2) V-1 s(-1), comparable to that of the c-Al2O3/STO interface. There has been evidence of oxygen-vacancy-related magnetism in gamma-Al2O3/STO at temperatures below 5K, while the enhanced AHE in NiAl2O4/STO and CoAl2O4/STO likely comes from the magnetic proximity effect induced by the top ferromagnetic MAl2O4 spinel films. Published by AIP Publishing.