Critical thickness for ferromagnetismin LaAlO_3/srTiO_3 heterostructures

摘要

In LaAlO_3/srTiO_3 heterointerfaces, charge carriers migrate from the LaAlO_3to the interface in an electronic reconstruction. magnetism has been observed in LaAlO_3/srTiO_3, but its relationship to the interface conductivity is unknown. Here we show that reconstruction isnecessary, but not sufficient, for the formation of magnetism. using scanning superconductingquantum interference device microscopy we find that magnetism appears only above a criticalLaAlO_3 thickness, similar to the conductivity. We observe no change in ferromagnetism withgate voltage, and detect ferromagnetism in a non-conducting p-type sample. These observationsindicate that the carriers at the interface do not need to be itinerant to generate magnetism. Theferromagnetism appears in isolated patches whose density varies greatly between samples.This inhomogeneity strongly suggests that disorder or local strain generates magnetism ina population of the interface carriers.