New magnetic order revealed in α-RuCl₃ at intermediate magnetic fields using neutron diffraction

It is well-known that an external magnetic field can induce a transition in α-RuCl₃ from a magnetically ordered state to a disordered state that may be related to the Kitaev quantum spin liquid. The overall temperature - magnetic field phase diagram of α-RuCl₃ is currently under intense scrutiny, and presently there is no universal agreement on the number of field induced phase transitions between the zero-field state and the high field polarized paramagnet. Single crystals with minimal stacking faults show a transition near T_N = 7 K at B = 0 T to a low temperature ordered phase that has a zigzag AFM structure in a single honeycomb layer, with a 3-fold periodicity perpendicular to the planes. For fields applied in the honeycomb plane perpendicular to a Ru-Ru bond there is evidence from magnetization, AC susceptibility, thermal transport [1], and magnetocaloric effect [2] data for an intermediate-field phase with a different magnetic order that precedes the disordered phase. Here we discuss neutron diffraction data that clarifies the magnetic structure in this phase. The intermediate ordered phase puts additional constraints on the minimal model magnetic Hamiltonian for α-RuCl₃.
[1] P. Lampen-Kelley et al, arXiv:1807.06192 (2018).
[2] C. Balz et al, Phys. Rev. B 100, 060405 (2019).