Robust Anomalous Hall Effect in Epitaxial Cubic D0$_3$-Fe$_3$Ge Nanoplates Grown by Chemical Vapor Deposition

Abstract

The iron-based ferromagnetic materials have emerged as a promising system for spintronics due to their high Curie temperatures and significant anomalous Hall effect (AHE) driven by Berry curvature. While there have been investigations into the epitaxial growth of non-layered iron-based ferromagnetic materials, the realization of high-quality single crystal thin films continues to be a formidable obstacle. Meanwhile, the issues such as grain boundary scattering further hinder their characterization and application. Here, we report the first chemical vapor deposition (CVD) synthesis of single-crystalline cubic D0$_3$-Fe$_3$Ge nanoplates. This compound represents a substantial departure from the conventional hexagonal phases typically observed in the Fe-Ge system. Structural characterizations confirm the cubic lattice and stoichiometric purity of the crystals. Structural analysis identifies a strong epitaxial effect, resulting in a giant compressive strain of ~4.16% at the interface that relaxes gradually toward the surface. The second-harmonic generation (SHG) signals might further reveal that such interfacial strain disrupted the inherent centro-symmetry of the cubic phase. SQUID magnetometry shows robust room-temperature ferromagnetism and clear magnetic anisotropy. Magneto-transport measurements reveal a robust AHE that remains stable at temperatures far exceeding room temperature. The scaling observed between the anomalous Hall resistance and longitudinal resistance strongly suggests that this effect is dominated by the intrinsic Berry curvature mechanism. Furthermore, density functional theory (DFT) calculations reveal that the huge epitaxial strain induces band reconstructions and creates dense spin-orbit coupling gaps near the Fermi level, effectively doubling the anomalous Hall conductivity to match our experimental observations.