In 2D magnets, interlayer exchange coupling is generally weak due to the van der Waals layered structure but it still plays a vital role in stabilizing the long‐range magnetic ordering and determining the magnetic properties. Using complementary neutron diffraction, magnetic, and torque measurements, the complete magnetic phase diagram of CrPS4 crystals is determined. CrPS4 shows an antiferromagnetic ground state (A‐type) formed by out‐of‐plane ferromagnetic monolayers with interlayer antiferromagnetic coupling along the c axis below TN = 38 K. Due to small magnetic anisotropy energy and weak interlayer coupling, the low‐field metamagnetic transitions in CrPS4, that is, a spin‐flop transition at ≈0.7 T and a spin‐flip transition from antiferromagnetic to ferromagnetic under a relatively low field of 8 T, can be realized for H∥c. Intriguingly, with an inherent in‐plane lattice anisotropy, spin‐flop‐induced moment realignment in CrPS4 for H∥c is parallel to the quasi‐1D chains of CrS6 octahedra. The peculiar metamagnetic transitions and in‐plane anisotropy make few‐layer CrPS4 flakes a fascinating platform for studying 2D magnetism and for exploring prototype device applications in spintronics and optoelectronics.

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The long‐range magnetic ordering in frustrated magnetic systems is stabilized by coupling magnetic moments to various degrees of freedom, for example, by enhancing magnetic anisotropy via lattice distortion. Here, the unconventional spin‐lattice coupled metamagnetic properties of atomically‐thin CrOCl, a van der Waals antiferromagnet with inherent magnetic frustration rooted in the staggered square lattice, are reported. Using temperature‐ and angle‐dependent tunneling magnetoconductance (TMC), in complementary with magnetic torque and first‐principles calculations, the antiferromagnetic (AFM)‐to‐ferrimagnetic (FiM) metamagnetic transitions (MTs) of few‐layer CrOCl are revealed to be triggered by collective magnetic moment flipping rather than the established spin‐flop mechanism, when external magnetic field (H) enforces a lattice reconstruction interlocked with the five‐fold periodicity of the FiM phase. The spin‐lattice coupled MTs are manifested by drastic jumps in TMC, which show anomalous upshifts at the transition thresholds and persist much higher above the AFM Néel temperature. While the MTs exhibit distinctive triaxial anisotropy, reflecting divergent magnetocrystalline anisotropy of the c‐axis AFM ground state, the resulting FiM phase has an a‐c easy plane in which the magnetization axis is freely rotated by H. At the 2D limit, such a field‐tunable FiM phase may provide unique opportunities to explore exotic emergent phenomena and novel spintronics devices.

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