Visualization of magnetic domain structure changes induced by interfacial strain in CoFe2O4/BaTiO3 heterostructures

We visualized the evolution of the magnetic domain structure in CoFe 2 O 4 films on different structural phases of BaTiO 3 substrates with {0 0 1} orientation, using variable temperature magnetic force microscopy. When BaTiO 3 underwent transitions from rhombohedral to orthorhombic to and from orthorhombic to tetragonal structures with increasing temperature, only local variations to the magnetic domains were observed. At the BaTiO 3 tetragonal–cubic transition however, the magnetic domain size increased by 75% with an overall decrease in stray field contrast (33% decrease) because of reorientation of the magnetization to the in-plane directions. The reorientation of magnetization during the tetragonal to cubic phase transition of BaTiO 3 was induced by release of asymmetric interfacial strain between the CoFe 2 O 4 film and the BaTiO 3 substrate, as non-uniformly distributed a and c surface ferroelectric domains in the BaTiO 3 tetragonal phase disappeared at the paraelectric BaTiO 3 cubic phase transition. Strain analysis based on macroscopic magnetization measurements was correlated with the microscopic magnetic domain structure to help understand the coupling in two-phase multiferroicheterostructure mediated by interfacial strain.