In LaAlO3/SrTiO3 heterointerfaces, charge carriers migrate from the LaAlO3 to the interface in an electronic reconstruction. Magnetism has been observed in LaAlO3/SrTiO 3, but its relationship to the interface conductivity is unknown. Here we show that reconstruction is necessary, but not sufficient, for the formation of magnetism. Using scanning superconducting quantum interference device microscopy we find that magnetism appears only above a critical LaAlO3 thickness, similar to the conductivity. We observe no change in ferromagnetism with gate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observations indicate that the carriers at the interface do not need to be itinerant to generate magnetism. The ferromagnetism appears in isolated patches whose density varies greatly between samples. This inhomogeneity strongly suggests that disorder or local strain generates magnetism in a population of the interface carriers.
Bibliographical noteFunding Information:
We thank Chuck Hitzman for his help with the NanoSIMS measurements, and Martin E. Huber for assistance in SQUID design and fabrication. We thank A.J. Millis, J. Mannhart, S. Raghu, and G.A. Sawatzky for helpful discussions. This work was primarily supported by U.S. DOE, Division of Materials Sciences, under Award No. DE-AC02-76SF00515. B.K. acknowledges support from FENA-MARCO contract No. 0160SMB958. The CAMECA NanoSIMS was acquired with support from NSF ECCS-0922648.