Noncollinear magnetic order in the S=12 magnet Sr₃ZnRhO ₆

The compound Sr₃ZnRhO₆ with S=1/2 belongs to a family of pseudo-one-dimensional (1D) spin-chain systems with general formula A ₃A⊃′BO₆. The nature of the ground state of Sr₃ZnRhO₆ is investigated using microscopic techniques such as muon spin relaxation (μSR) and powder neutron diffraction in addition to bulk characterization using magnetization, ac-susceptibility, and heat capacity. Our μSR study clearly reveals the presence of three frequencies, below 16 K, whose temperature dependence follow a mean-field order parameter indicating long-range magnetic ordering of the Rh4⊃+ moment. Powder neutron diffraction reveals the presence of four weak magnetic Bragg peaks below 16 K, indexed by the propagation vector k=(0,12,1) in the hexagonal setting of the space group R3c. Analysis of the magnetic diffraction pattern constrained to symmetry-adapted magnetic modes reveals a noncollinear magnetic structure with an ordered magnetic moment of Rh4⊃+=0.7(1) μ_B. This is the first compound in this spin chain family which exhibits noncollinear magnetic order with the moment tilting away from the c axis, highlighting the important role of interchain and intrachain interactions.