Spontaneous magnetization reversal and positive exchange bias effect in CoFeSiB/FeCrO3 heterostructures

Exchange bias (EB) phenomena is an interface driven effect, it depends on the interface spin configuration, which in turn is immensely related to AFM spin configuration. Here, we chose an antiferromagnet, FeCrO3having corroundum structure with randomly occupaid cations. We report exchange bias in the bilayer heterostructures composed of amorphous CoFeSiB ferromagnet interfaced with epitaxial FeCrO3layer fabricated in-situ by pulsed laser deposition. The bilayers exhibit crossover from conventional negative EB to positive from room temperature down to 5 K. The crossover occurs for cooling field that exceeds the interfacial coupling strength at the interface. Systems that show positive EB effect sometimes also display spontaneous magnetization reversal; the present bilayers showed spontaneous exchange bias below 50 K. Temperature and field-dependent magnetisation studies reveal that the prepared heterostructure consists of uncompensated interface spins due to the disorder in FeCrO3layer that gets frozen at low temperatures pin the spins in the ferromagnetic layer and causes the spontaneous EB effect.