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Abstract:
We present a comprehensive experimental and theoretical study of the structural, electronic, magnetic, and thermodynamic properties of a Pb6Co9(TeO6)(5) single crystal. The Pb6Co9(TeO6)(5) crystal has shown a unique type of magnetic spin-lattice coupling, in which the lattice structure consists of four different Co ions sites with distorted octahedral coordinations. The x-ray photoelectron spectroscopy (XPS) results confirmed the oxidation states of Pb, Co, Te, and O elements in the sample. Moreover, XPS spectra revealed the adsorbed oxygen in the defect/vacancy sites of the lattice structure. The dc magnetization measurements exhibited a complex magnetic behavior with ferrimagnetic (FIM) transition with Curie temperature T-C at similar to 21 K. At lower magnetic fields H, the zero-field-cooled and field-cooled curves showed a broad hump at similar to 10.8 K and a shoulder peak at similar to 6.2 K, which are suppressed at higher magnetic fields. The ac susceptibility data indicated spin-glass-like features. The heat capacity C-P measurements confirmed the FIM transition at T-C at similar to 21 K, but without any trace of additional peaks at lower temperatures. The estimated Curie-Weiss constant theta(CW) showed a peculiar field-dependent behavior along the H parallel to c direction of the single crystal, where theta(CW) is less field dependent for the H perpendicular to c direction. A large coercivity (13 kOe) is observed at 2 K for H parallel to c, whereas the magnetization curve of the single crystal is dominated by an antiferromagnetic feature for H perpendicular to c. The behaviors indicate the anisotropy nature of the exchange interactions in the compound. The local spin density approximation + U total energy calculations were performed for various collinear spin configurations of a classical Heisenberg model in order to obtain the magnetic exchange interactions J(i) at different distances for different neighbors.
