Structure transition and zigzag magnetic order in Ir/Rh-substituted honeycomb lattice -RuCl₃

We report magnetization and neutron diffraction studies on crystal and magnetic structures of Ir- and Rh-substituted honeycomb lattice alpha-RuCl3. The iridium or rhodium atoms are distributed at the Ru site with little structural modification. Both systems undergo a room-temperature monoclinic C2/m to low-temperature trigonal R3 over bar phase transformation with a large recoverable hysteresis. At low temperature, a zigzag spin order is observed with the same characteristic wave vector (0,0.5,1) as in the parent alpha-RuCl3. Detailed magnetic structure refinement reveals an ordered moment of 0.32(5)mu B/Ru and an upper boundary of canting angle of 15(4)degrees away from the basal plane at 5 K for the 10% Ir-substituted alpha-RuCl3, which is different from the 0.45-0.73 mu B/Ru and 32 degrees-48 degrees canting angle reported in the parent compound alpha-RuCl3. The observation of unchanged RuCl6 local octahedral environment, reduced ordered magnetic moment size and canting angle compared to previously reported highlights the potential to study quantum spin-liquid behavior through nonmagnetic ion doping.