Room Temperature Multiferroicity in Bi-Doped ZnO Enabled by Lattice Distortion and Electronic Reconstruction

Multiferroic materials that simultaneously exhibit ferroelectric and ferromagnetic order are highly attractive for multifunctional logic, memory, and spintronic devices. Here, we demonstrate robust room temperature multiferroicity in Bi doped ZnO (ZnBi_0.05O_0.95) thin films grown by pulsed-laser deposition. Structural analyses using XRD, HR-TEM, and Raman spectroscopy unequivocally confirm single phase, c-axis-oriented wurtzite ZnO substitutional incorporation of Bi and no secondary phases. Ferroelectric switching behavior is verified through piezo-response force microscopy (PFM), polarization-electric field (P-E), and current-voltage (I-V) measurements, yielding a remnant polarization of 0.36 µC cm^-2 and coercive field of 125 kV cm^-1. Concurrently, magnetization studies reveal robust ferromagnetism persisting above 350 K. To elucidate the microscopic origin of the multiferroicity, X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) reveal a Bi-induced downward shift of O 2p band edge together with pronounced modifications in the O 2p-Zn hybridized states. These spectroscopic observations indicate Bi-driven lattice distortion, hole introduction, and emergence of spin-polarized Bi states. These cooperative structural and electronic reconstructions underpin the multiferroic response in ZnBi_0.05O_0.95, establishing this material as a promising silicon-compatible multiferroic semiconductor for next-generation multifunctional device technologies.