Pressure-induced ferromagnetism in the topological semimetal EuCd₂As₂

The antiferromagnet and semimetal EuCd2As2 has recently attracted a lot of attention due to a wealth of topological phases arising from the interplay of topology and magnetism. In particular, the presence of a single pair of Weyl points is predicted for a ferromagnetic configuration of Eu spins along the c axis in EuCd2As2. In the search for such phases, we investigate here the effects of hydrostatic pressure in EuCd2As2. For that, we present specific heat, transport, and mu SR measurements under hydrostatic pressure up to similar to 2.5 GPa, combined with ab initio density functional theory (DFT) calculations. Experimentally, we establish that the ground state of EuCd2As2 changes from in-plane antiferromagnetic (AFM(ab)) to ferromagnetic at a critical pressure of approximate to 2 GPa, which is likely characterized by the moments dominantly lying within the ab plane (FMab). The AFM(ab)-FMab transition at such a relatively low pressure is supported by our DFT calculations. Furthermore, our theoretical results indicate that EuCd2As2 moves closer to the sought-for FMc state (moments parallel to c) with increasing pressure further. We predict that a pressure of approximate to 23 GPa will stabilize the FMc state if Eu remains in a 2+ valence state. Thus, our work establishes hydrostatic pressure as a key tuning parameter that (i) allows for a continuous tuning between magnetic ground states in a single sample of EuCd2As2 and (ii) enables the exploration of the interplay between magnetism and topology and thereby motivates a series of future experiments on this magnetic Weyl semimetal