Magnetism of single crystal α-RuCl₃ investigated by muon spin rotation

We have performed muon spin rotation measurements on single crystal α-RuCl₃, a honeycomb layered ruthenate that has been proposed to be close to a Kitaev quantum spin liquid ground state. Our investigation finds a single transition to long range magnetic order near $8$~K, in contrast to the two distinct transitions we previously observed in muon spin rotation measurements of a α-RuCl₃ powder sample [Lang et al, PRB 94 (2016) 020407(R)]. We interpret this in the light of a structural phase transition that has been recently discovered in high purity single crystals of this material. By employing density functional theory calculations we identify the likely muon stopping sites in this material and combine these with dipolar field calculations to investigate which previously reported zigzag antiferromagnetic structures are consistent with the two experimentally observed muon rotation frequencies.