Powder-neutron-diffraction study of magnetic structure on frustrated Ba3MnTa2O9

Two- dimensional (2D) triangular lattice antiferromagnets (TLAF) offer exotic magnetic phases and have attracted a lot of attention in recent times. A new Mn2+ (S=5/2) based TLAF Ba3MnTa2O9 has been synthesized in polycrystalline form using a solid-state reaction method and characterized using HRXRD, dc, and ac susceptibility and heat capacity measurements. Rietveld refinement of XRD data suggests that the material crystallizes in a trigonal crystal structure with space group P-3m1. The crystal structure comprises edge-shared triangular layers of Mn2+ ions in the crystallographic ab-plane which are well separated (7.1252 Å) along the crystallographic c-direction making it effectively a 2D TLAF. The Curie-Weiss fit of susceptibility above 100 K yields θCW ~ -10 K, indicating a dominant antiferromagnetic interaction between Mn2+ ions. The effective magnetic moment (µeff ~ 5.8 µB) is close to the theoretical value of ~5.9 µB for isolated Mn2+ ions. A hump at ~3K in ac susceptibility (χ’) and heat capacity data suggest the onset of a magnetic ordering. The neutron powder diffraction technique will be useful for studying the spin structure of Ba3MnTa2O9 in the ordered state.