Vehement Competition of Multiple Superexchange Interactions and Peculiar Magnetically Disordered State in Cu(OH)F

Abstract

The mixed anion copper compound Cu(OH)F was studied in measurements of magnetic susceptibility, static and pulsed field magnetization, specific heat, X-band electron magnetic resonance and muon-spin spectroscopy. In variance with its layered structure, the magnetic behavior shows no evidence of low-dimensionality. Cu(OH)F reaches short range static antiferromagnetic order at TN = 9.5  11.5 K and experiences the spin-flop transition at B ~ 3.5 T. This behavior is in a sharp contrast with physical properties of earlier reported isostructural compound Cu(OH)Cl. The first principle calculations reveal highly competitive nature of ferromagnetic and antiferromagnetic superexchange interactions, the details being rather sensitive to choice of magnetic structure employed in the extraction of magnetic interaction. Rather broad anomaly in Cp(T) dependence at phase transition and smeared magnetization curve M(B) at low temperatures suggest static disorder in the ground state. Zero-field μSR data are consistent with Cu(OH)F experiencing a transition into a static magnetically disordered state. 1.Introduction Among numerous building blocks of inorganic chemistry the polyhedral units of divalent copper in oxygen coordination attract most attention in a quest for low dimensional magnetism and superconductivity.1) The copper polyhedra appear to be heavily distorted due to Jahn -Teller effect inherent for electronic 3d 9 shell of Cu 2+ ions. The pseudo-octahedral coordination units CuO6 may differ in their distortion. It could show symmetric or asymmetric shortening and elongation of basal and apical bonds. The positions of the apical ligands may heavily deviate from the normal to the basal plane and the basal plane itself may be bent. In this sense, better description for these units could be given in terms of pyramids CuO5, pseudo-tetrahedral CuO4 units or planar squares CuO4.2) The lower coordination of copper facilitates the reduced dimensionality of magnetic subsystem in the crystal structure. In complex oxides, the copper polyhedra linked through corners, edges or faces frequently form isolated chains or layers separated by nominally non-magnetic structural units. These quasi-onedimensional and quasi-two-dimensional structures develop short-range correlations but may be prevented from reaching a long-range magnetic ordered state. The non-magnetic units providing rather efficient pathways for the exchange interactions help to overcome this difficulty which may result in formation of three-dimensional magnetic order at lowering temperature.3) Similarly the tendency to form low-dimensional magnetic structures is rather pronounced in complex cupric halides and the role of side groups is also important in these compounds.Despite the fact, that both cupric oxide CuO and cupric halides CuX2 (X = F, Cl, Br) have been the topic of research due to their low dimensional magnetic structures, there is renewed interest in these compounds. To some extent, this is due to observation of multiferroicity in these compounds. [4][5][6] In spi...

Strongly canted antiferromagnetic ground state in Cu3(OH)2F4

“…At the same time, in such cases no exchange pathways are present with participation of other transition and non-transition cations which simplifies the analysis of exchange interactions. The basic families of 3d-metals polyanion compounds are the oxyhalides MOX (M = Sc  Cr and Fe; X = Cl and Br) [1][2][3][4][5], the hydroxyhalides M(OH)X (M = Co and Cu; X = F and Cl) [6][7][8] and the trihydroxyhalides M2(OH)3X (M = Mn  Cu; X = Cl and Br) [9][10][11].…”

Compression Behavior of Copper Hydroxyfluoride CuOHF as a Case Study of the High-Pressure Responses of the Hydrogen-Bonded Two-Dimensional Layered Materials

“…The Brillouin zone was sampled by 8 × 7 × 8 special k points using the Monkhorst–Pack scheme for structural optimization and line model for the density of states (DOS) and band structure calculations. Because the d orbitals play an important role in transition metals, the U (on-site coulomb term) value for Cu 3d was set at 8 eV (Table S2), which is determined using the linear response theory considered in previous work . Ferromagnetically spin-polarized, antiferromagnetically spin-polarized, and nonspin-polarized DFT calculations were used to optimize the structures at room pressures.…”