Emergence of Room Temperature Magnetotransport Anomaly in Epitaxial Pt/γ'-Fe₄N/MgO Heterostructures toward Noncollinear Spintronics

Noncollinear spin textures have attracted much attention due to their novel physical behaviors in heavy/ferromagnetic metal (HM/FM) systems. The transport anomaly, appearing as contrast humps in Hall resistivity curves, is the mark of noncollinear spin textures. Here, the epitaxial Pt/γ'-Fe₄N bilayers with noncollinear spin textures were obtained by facing target sputtering. Large micromagnetic Dzyaloshinskii-Moriya interaction coefficient D of 2.90 mJ/m² appears in Pt/γ'-Fe₄N/MgO systems, which is larger than 2.05 mJ/m² of Pt/Co/MgO systems with skyrmionic states. Moreover, at 300 K, magnetic bubble-like domains appear in Pt/γ'-Fe₄N bilayers that just possess a 3 nm thick ferromagnetic layer instead of [HM/FM]_n or [HM₁/FM/HM₂]_n multilayers. Additionally, a room-temperature transport anomaly appears in Pt/γ'-Fe₄N/MgO systems. The contrast humps of Pt(3 nm)/γ'-Fe₄N(t_Fe4N ≤ 4 nm)/MgO heterostructures are not sharp due to the nonuniform distributions of the magnetic bubble-like domains with various sizes and irregular shapes, as observed by the magnetic force microscopy. The discovery of epitaxial Pt/γ'-Fe₄N bilayers with noncollinear spin states is more crucial than that of polycrystalline or amorphous HM/FM systems for reducing ohmic heating, which provides a candidate for noncollinear spintronic applications.