Van der Waals (vdW) magnetic materials have emerged as a promising platform for investigating low-dimensional magnetism and developing next-generation spintronic devices. Among them, all-ferromagnetic heterojunctions, such as the Fe₃GaTe₂/Fe₃GeTe₂ (FGaT/FGT) system, exhibit intriguing magneto transport phenomena, including multi-step transitions and antisymmetric magnetoresistance (MR) peaks under perpendicular magnetic fields. However, the underlying physical mechanisms governing these complex behaviors remain elusive. This study aims to elucidate the origin of the antisymmetric MR in FGaT/FGT vdW heterojunctions, focusing on the interplay between the anomalous Hall effect (AHE), interfacial oxidation, and temperature-dependent interlayer coupling.
High-quality FGaT/FGT heterojunction devices were fabricated using mechanical exfoliation and dry transfer techniques. The magneto transport properties were systematically characterized from 5 K to 190 K using a Physical Property Measurement System (PPMS). The experimental results, combined with an equivalent circuit model analysis, reveal that the antisymmetric MR signal primarily stems from a local non-equilibrium current driven by a mismatch in the AHE voltages generated across the top (FGT) and bottom (FGaT) ferromagnetic layers when their magnetizations are non-collinear. This voltage imbalance significantly modulates the longitudinal resistance (Rxx), producing the characteristic sharp MR peaks near zero field.
Furthermore, detailed analysis of the individual FGaT layer uncovers a two-stage magnetization reversal process, attributed to the coexistence of a magnetically distinct interface region, influenced by a naturally formed antiferromagnetic O-FGaT oxide layer, and the FGaT bulk region. This interfacial oxidation induces an exchange bias effect, which is responsible for the observed asymmetry and multi-step transitions in the heterojunction's MR hysteresis loops. Temperature-dependent measurements demonstrate that the antisymmetric MR diminishes upon heating, evolving into a smooth, paramagnetic-like background above 180 K. This transition highlights the suppression of the AHE-driven non-equilibrium transport and the interlayer decoupling as thermal fluctuations reduce magnetic anisotropy.
In conclusion, our work demonstrates that the antisymmetric MR in FGaT/FGT heterojunctions arises from the synergistic effects of AHE-induced circulating currents, interface oxidation-mediated exchange bias, and thermally activated layer decoupling. These findings provide a comprehensive understanding of the charge transport mechanisms at magnetic vdW interfaces and offer valuable insights for the design of future multi-state spintronic devices based on interface and domain engineering.