Structural and magnetic properties on F-doped LiVO 2 with two-dimensional triangular lattice
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Structural and magnetic properties on F-doped LiVO2 with two-dimensional triangular lattice Yang Li 1,2,∗, Xiaoxiang Li 2, Lihua Liu 2, Ning Chen 3, Jose García 1, Rafael Dávila 1, Danny Faica 1, Alfred Rivera 1, Pedro Rodríguez 1, Rubén Pérez 1 and Guohui Cao 2 1
Department of Engineering Science and Materials, University of Puerto Rico at Mayaguez, Mayaguez, PR 00681-9044, U.S.A. 2 Department of physics, University of Science and Technology Beijing, Beijing 100083, China 3 School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China ABSTRACT The layered oxide LiVO2 recently has received more attention due to its interesting structural and magnetic behaviors involving the two-dimensional magnetic frustration in these systems. We synthesized a series of F-doped LiVO2 samples, and reported the F-doping effect on the structure and transition temperature Tt. The samples LiVO2-xFx (x=0, 0.1, 0.2 and 0.3) were characterized by X-ray diffraction, scanning electron microscope (SEM), differential scanning calorimetry (DSC), magnetic susceptibility and specific heat measurement. The structural analysis shows that with increasing x, the ratio of lattice parameter c/a increasing, i.e. in the a-b plane the lattice is compressed while in the c-axis direction the lattice expands. The DSC measurements show that a first-order phase transition happens at around 500 K, and the thermal hysteresis around phase transition temperature Tt increases with increasing x. Substitution of O with F ions results in a change of two dimensional characteristics and the distortion of the VO6 block in structure, which significantly influence the magnetic ordering transition temperature Tt. INTRODUCTION There is a great deal of interest in the transition metal compound LiVO2 with twodimensional triangular lattice, due to it exhibits peculiar structural and magnetic behaviors involving the magnetic frustration. For LiVO2 an orbital ordering transition occurs near 500 K, which leads to a suppression of magnetic moment below this transition temperature Tt [1,2,3]. Magnetic V3+ (S=1) ions with partly filled t2g orbitals in this compound occupy the sites of a triangular lattice [4,5,6]. The system forms an orbitally ordered state at low temperatures [2,7,8]. LiVO2 crystallizes into a rhombohedral structure (as shown in Fig. 1) with hexagonal dimensions a = 2.83 and c =14.87 Å [space group R 3m (No.166)], in which the distribution of ions can be represented by (Li+)[V3+]O22-. The V-O coordination is octahedral VO6 site. The Li, V and O layers stack along c-axis direction. Each of these layers forms a triangular two-dimensional lattice. LiVO2 exhibits a first order magnetic phase transition [9] at around Tt = 500 K. The interesting property is a change from a high temperature paramagnetic phase with a large negative Curie-Weiss temperature Ĭ = -1800 K in χ ∝ 1 /(T + Θ) , corresponding to a large antiferromagnetic coupling, to a low temperature “nonmagnetic system” without any sign of long-range order [10]. T
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