Ferromagnetism in a van der Waals Antiferromagnet via Anisotropy Engineering

The van der Waals antiferromagnets MPX₃ (M = magnetic metal element, X = S or Se) are a premier class of materials for studying low-dimensional magnetism, as they retain magnetic order in atomically thin or even in monolayers. Their antiferromagnetic ground state, however, possesses no net moment, making the atomic-scale detection and control of magnetism a fundamental challenge. Establishing robust ferromagnetism in MPX₃ would therefore be a critical advance for spintronics and magneto-optoelectronics. Although chemical substitution of the metal ion (M) efficiently tunes magnetic properties, it typically preserves the antiferromagnetic order. Here we propose and demonstrate a different approach by harnessing the competition between magnetic ions with strong and distinct single ion anisotropies to drive a ferromagnetic transition. By mixing highly anisotropic Fe²⁺ and Co²⁺ ions to create (Fe,Co)PS₃, we observe the emergence of ferromagnetism. This anisotropy engineering strategy presents a general and efficient route to induce ferromagnetism in layered antiferromagnets, broadening their prospects for both fundamental science and device applications.