title: BaMn9[VO4]6(OH)2: a unique canted antiferromagnet with a chiral "paddle-wheel" structural feature.
abstract: BaMn(9)[VO(4)](6)(OH)(2) was synthesized by hydrothermal methods. We evaluated the crystal structure based on the two possible space groups P2(1)3 and Pa3̅ [a = 12.8417(2) Å] using single-crystal and powder X-ray diffraction techniques. The structure contains three-dimensionally linked Mn(9) units of a chiral "paddle-wheel" type. Experimental IR and Raman spectra were analyzed in terms of fundamental vanadate and hydroxide vibrational modes. The magnetic properties were investigated, and the specific heat in applied fields was studied. The dominant magnetic interactions (Mn(2+), S = 5/2) are of antiferromagnetic origin, as indicated by a Curie-Weiss fit above 175 K with Θ ≈ -200 K. Canting of the spins on the geometrically frustrated triangle segment of the structural feature is considered to account for the ferrimagnetic type of long-range order at T(C) ≈ 18 K. We propose a model for the spin structure in the ordered regime. Dielectric constants were measured and indicate a magnetodielectric effect at T(C), which is assigned to spin-lattice coupling.
authors.affiliation: Department of Chemistry and Texas Center for Superconductivity, University of Houston , Houston, Texas 77204-5003, United States.
authors.forename: Kewen
authors.initials: K
authors.lastname: Sun
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Litvinchuk
authors.forename: Joshua
authors.initials: J
authors.lastname: Tapp
authors.forename: Bernd
authors.initials: B
authors.lastname: Lorenz
authors.forename: Angela
authors.initials: A
authors.lastname: Möller