Multiple magnetic phases investigated via critical behavior in van der Waals antiferromagnet Co-doped Fe5GeTe2

Two-dimensional van der Waals magnets FenGeTe2 (FnGT) provide an ideal platform for exploring low-dimensional magnetism and developing high-performance room-temperature spintronic devices due to their prominent intrinsic ferromagnetism and significant magnetic anisotropy. Herein, we systematically investigate the multiple magnetic phases of Co-doped F5GT (FCGT with 38% Co) single crystals. We found that Co-doping induces multiple magnetic orderings within the intrinsic ferromagnetic (FM) matrix, consisting of intralayer ferrimagnetic coupling and interlayer antiferromagnetic (AFM) coupling. The distinct spin responses of Co and Fe sublattices enable field-dependent sequential spin-flipping behaviors, which can be independently tuned by external magnetic fields and remain thermally robust up to 340 K. Angular-dependent magnetization studies further confirm the field-driven spin-flipping behaviors. Quantitative critical behavior analysis indicates that FCGT belongs to the 3D-Heisenberg universality class, with nearly isotropic magnetic exchange interactions decaying spatially as J(r)∼r−4.94. Subsequently, we established a quantitative magnetic phase diagram of FCGT for H//c, which clearly resolves the boundaries of successive field-induced phase transitions and characterizes the coexistence and canted regimes of multiple magnetic phases. This work clarifies the atomic-modulated magnetic interactions in FnGT systems, offering valuable insights for designing room-temperature tunable FM and AFM spintronic devices based on modified vdW magnetic materials.