Abstract
HfCuSi(2)-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 A(2+)M(2+)Pn(2) and A(3+)M(+)Pn(2) (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 UCu(x)Bi(2) single crystals and study their magnetic properties. Detailed structural analysis revealed that flux-grown crystals always form as a site-deficient UCu(x)Bi(2) 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 UCu(0.60)Bi(2) to 118 K for UCu(0.30)Bi(2). Moreover, higher Cu concentration promotes a metamagnetic transition in highly magnetically anisotropic UCu(0.60)Bi(2) single crystals. We show that DFT calculations can successfully model site deficiency in the UCu(x)Sb(2) and UCu(x)Bi(2) systems. This work paves the way toward using the site deficiency to tune the Fermi level in more ubiquitous A(3+)M(2+)(x)Pn(2) phases, which previously have not been considered topological candidate materials due to unfavorable electron count.