Abstract
HfCuSi2-type pnictogen compounds have recently been shown to be a versatile platform for designing materials with topologically nontrivial band structures. However, these phases require strict control over the electron count to tune the Fermi level, which can only be achieved in compositions with A2+M2+Pn2 and A3+M+Pn2 (A = lanthanides, M = transition metals, Pn = pnictogens P–Bi) charge distribution. While such lanthanide compounds have been thoroughly studied as candidate magnetic topological materials, their heavy element analogs with uranium and bismuth remain largely underexplored. In this report, we present the synthesis of UCuxBi2 single crystals and study their magnetic properties. Detailed structural analysis revealed that flux-grown crystals always form as a site-deficient UCuxBi2 composition, where x varies between 0.20 and 0.64. Magnetic property measurements revealed a dependence of the magnetic coupling on the Cu site deficiency, linearly changing the Néel temperature from 51 K for UCu0.60Bi2 to 118 K for UCu0.30Bi2. Moreover, higher Cu concentration promotes a metamagnetic transition in highly magnetically anisotropic UCu0.60Bi2 single crystals. We show that DFT calculations can successfully model site deficiency in the UCuxSb2 and UCuxBi2 systems. This work paves the way toward using the site deficiency to tune the Fermi level in more ubiquitous A3+M2+xPn2 phases, which previously have not been considered topological candidate materials due to unfavorable electron count.
