Observation of room-temperature multiferroicity with strong magnetoelectric coupling in hafnia thin films

HfO₂-based ferroelectrics have emerged as promising candidates for next-generation information devices due to their excellent compatibility with complementary metal oxide semiconductor technology. However, achieving room-temperature multiferroicity in single-phase HfO₂-based materials remains a rewarding yet challenging goal. Here, we report the discovery of room temperature multiferroicity in single-phase Cr-doped HfO₂ films. We demonstrate a direct correlation between ferroelectric and ferromagnetic orders; films with stronger ferromagnetism exhibit enhanced ferroelectricity. Crucially, the application of external magnetic fields induces a significant boost in both ferroelectric polarization and piezoresponse amplitude. A giant magnetoelectric coupling coefficient of ~100 Vcm^-1Oe^-1 is obtained, surpassing those of most previously reported single-phase multiferroic materials at room temperature. Our results not only establish Cr-doped HfO₂ films as a promising platform for exploring emergent multiferroic phenomena but also pave the way for a new class of silicon-compatible magnetoelectric devices.