Exotic Ferroelectric and Multiferroic Properties in Epitaxial YFeO3 Thin Films and YFeO3-CoFe2O4 Nanocomposites

Multiferroics have been attracting considerable interest in the past decades, and researchers never stop searching for materials exhibiting multiferroic behavior. For orthoferrites, there should be no ferroelectricity in theory due to their centrosymmetric structure. However, when epitaxially grown, the strain can significantly modify the symmetry and physical properties. Here, we present the exotic ferroelectric properties of epitaxial YFeO3 (YFO) thin films on perovskite substrates prepared by pulsed laser deposition (PLD). A nearly single-domain structure is observed in as-grown 40 nm-thick YFO thin films characterized by Piezoresponse force microscopy (PFM), and it can be fully switched suggested by the ideal ferroelectric hysteresis loop and by domain patterns written by a bias of +/- 8 V. The spontaneous polarization direction is highly dependent on the epitaxial strain, which could be tuned either out-of-plane or in-plane. Via co-deposition by PLD, the nanocomposites consisting of YFO and CoFe2O4 (CFO) have been prepared, in which phase separation is successfully achieved. Both ferroelectricity and ferromagnetism are observed originating from YFO and CFO respectively, indicating a promising magnetoelectric coupling in this 2-phase multiferroic nanocomposite.