title: Novel Mixed Cobalt/Chromium Phosphate NaCoCr2(PO4)3 Showing Spin-Flop Transition.
abstract: We describe the synthesis and the crystallographic and magnetic properties of a novel NaCoCr2(PO4)3 phosphate. A conventional solid-state reaction was used to obtain single-phase powders. A Rietveld analysis of powder X-ray diffraction data proposes an orthorhombic symmetry similar to α-CrPO4-type structure in space group Imma with the following unit cell parameters: a = 10.413(1) Å; b = 13.027(1) Å; c = 6.372(1) Å. The framework consists of PO4 tetrahedra, M(1)O6 (M(1) = Cr) octahedra, and M(2)2O10 (M(2) = 0.5Cr+0.5Co) binuclear unit of edge-sharing MO6 octahedra. It can be described in terms of two building blocks: sheets consisting of corner-sharing M(2)2O10 units with PO4 tetrahedra found parallel to the (b,c) plane, and chains made by corner-sharing CrO6 octahedra and PO4 tetrahedra running along the b axis. From the interconnection of the sheets and chains, a 3D rigid skeleton is formed, exhibiting two kinds of intersecting tunnel channels containing the Na(+) ions. The proposed structure derives from the α-CrPO4-type structure considering a positive charge balance according to the equation Cr(3+) → Co(2+) + Na(+), resulting in sodium countercation introduction within the unoccupied channels shown in the α-CrPO4 framework. Temperature-dependent DC and AC magnetic susceptibility is indicative of a long-range magnetic ordering occurring at 32 K. Further, spin-flop transition sheds light on a chromium-based phosphate for the first time.
authors.affiliation: †Faculté des Sciences 5019, Monastir, Tunisie.
authors.forename: Khalifa
authors.initials: K
authors.lastname: Souiwa
authors.affiliation: ‡CNRS, Univ. Bordeaux, ICMCB, UPR 9048 F-33600, Pessac, France.
authors.forename: Madhu
authors.initials: M
authors.lastname: Chennabasappa
authors.affiliation: ‡CNRS, Univ. Bordeaux, ICMCB, UPR 9048 F-33600, Pessac, France.
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Decourt
authors.affiliation: †Faculté des Sciences 5019, Monastir, Tunisie.
authors.forename: Mongi
authors.initials: M
authors.lastname: Ben Amara
authors.affiliation: †Faculté des Sciences 5019, Monastir, Tunisie.
authors.forename: Mourad
authors.initials: M
authors.lastname: Hidouri
authors.affiliation: ‡CNRS, Univ. Bordeaux, ICMCB, UPR 9048 F-33600, Pessac, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Toulemonde