Effect of the thickness of BiFeO3 layers on the magnetic properties of BiFeO3/La2/3Sr1/3MnO3 heterostructures

BiFeO3 (BFO) thin films with different thicknesses were deposited on La0.67Sr0.33MnO3 (LSMO) buffered SrTiO3 (0 0 1) substrate using a pulsed laser deposition technique. The variation in the out-of-plane lattice parameter and magnetic properties of BFO/LSMO with various thicknesses of BFO are explored. The lattice parameter of BFO decreases with the increasing thickness of BFO and approaches to a value corresponding to bulk BFO. The remanent magnetization (Mr) and magnetic coercive field (Hc) of BFO/LSMO heterostructures depend on the thickness of the top layer BFO. The maximum values of Mr and HC in BFO/LSMO are observed for BFO with thickness (tBFO) equal to ∼25 nm. For tBFO > 25 nm, both Mr and Hc of BFO/LSMO decrease with increasing thickness of the BFO layer. Further, a wasp-waisted shape in the M-H loop of BFO/LSMO perceptible at a high temperature (100 K) may be originated from a new magnetic phase in the BFO layer at the interface due to Fe3+ and Mn3+/4+ magnetic interactions between the two layers. The exponential decay of the HC(T) with increasing temperature suggests the multiple competing interactions, such as Fe3+-O-Fe3+ and Fe3+-O-Mn3+/4+ and Mn3+/4+ -O-Mn3+/4+ leading to a spin-glass state in the interfacial region. The variations in the magnetic properties of BFO/LSMO with the thickness of BFO may be associated with the single domain to multi-domain transition and/or linked to the effect of the epitaxial strain, and Fe3+ and Mn3+/4+ magnetic interactions in the vicinity of the interface.