Influence of the Chemical Pressure on the Magnetic Properties of the Mixed Anion Cuprates Cu2OX2 (X = Cl, Br, I)

Abstract

In this study, we theoretically investigate the structural, electronic and magnetic properties of the Cu2OX2 (X = Cl, Br, I) compounds. Previous studies reported potential spin-driven ferroelectricity in Cu2OCl2, originating from a non-collinear magnetic phase existing below TN∼70 K. However, the nature of this low-temperature magnetic phase is still under debate. Here, we focus on the calculation of J exchange couplings and enhance knowledge in the field by (i) characterizing the low-temperature magnetic order for Cu2OCl2 and (ii) evaluating the impact of the chemical pressure on the magnetic interactions, which leads us to consider the two new phases Cu2OBr2 and Cu2OI2. Our ab initio simulations notably demonstrate the coexistence of strong antiferromagnetic and ferromagnetic interactions, leading to spin frustration. The TN Néel temperatures were estimated on the basis of a quasi-1D AFM model using the abinitioJ couplings. It nicely reproduces the TN value for Cu2OCl2 and allows us to predict an increase of TN under chemical pressure, with TN = 120 K for the dynamically stable phase Cu2OBr2. This investigation suggests that chemical pressure is an effective key factor to open the door of room-temperature multiferroicity.