Observation of Anomalously Large Magnetoelectric Coupling in the Hexagonal Z‐Type Ferrite Films

Although the bulk hexaferrites are known to exhibit strong magnetoelectric (ME) effects near room temperature, the same effects are not realized in a thin film form. Herein, the growth of nearly epitaxial Co2Z‐type hexaferrite Ba0.3Sr2.7Co2Fe24O41 (BSCFO) thin films on a SrTiO3 (111) substrate by a chemical solution deposition method is reported. The reciprocal space mapping on the annealed BSCFO films reveals broadening along the qx directions in the (0014) and (0018) peaks, indicating that the oxygen planes belonging to the off‐centered octahedra have randomly distributed out‐of‐plane tilt to indicate significant disorder in the crystallographic orientation. Quantitative investigations reveal that both ME susceptibility and modulated electric polarization (ΔP) by magnetic field up to 370 K in the BSCFO films are always larger than those of the Co2Z‐type single crystal by ≈2–15 times and further increase upon having enhanced qx broadening in the (0014) and (0018) peaks. As the off‐centered octahedral sites can be a primary source of ΔP as predicted by the p–d hybridization mechanism, these results indicate that effective off‐centering could be further enhanced by the orientational disorder. This study identifies the potential of applying the ME hexaferrite films for multifunctional devices. Nearly epitaxial hexaferrite Ba0.3Sr2.7Co2Fe24O41 thin films grown on SrTiO3 (111) exhibit always larger magnetoelectric (ME) coupling than those of similar single crystals by ≈2–15 times. Based on structural and field rotating ME susceptibility investigations, the enhanced ME coupling is attributed to the disorder in the oxygen planes, which are directly coupled to the enhanced polarization via the p–d hybridization mechanism.