Chemical expansion and physical pressure effects on the Kagome Cu3Bi(SeO3)2O2Cl

• Main Authors: Wu-chun Tseng, 曾武俊
• Other Authors: Hung-duen Yang
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/kps6gq

碩士 === 國立中山大學 === 物理學系研究所 === 105 === In recent years, the frustrated spin system has been a popular research topic. In these systems, the magnetic ions have confined to peculiar lattice geometries that exhibits the exotic physical properties under external magnetic field and pressure, which are very much different from the general magnetic materials. The common frustrated-spin lattices have triangular lattice, Kagome lattice, spinel structure and pyrochlore lattice. 　　The Cu3Bi(SeO3)2O2Cl, belongs to type II multiferroic material, the spin 1/2 Cu2+ ions form the pseudo-Kagome lattice, is an interesting spin-frustrated material. Apart from multiferroic behavior, it also exhibits anisotropic magnetic property. These unique magnetic and multiferroic properties motivated us to further understanding of these materials under the chemical/physical pressure conditions. Unit cell expansion studies were carried out with chemical doping of Te and Br ions at Se and Cl sites respectively. The physical pressure used for the compression studies. 　　The XRD (X-ray diffraction) data of the Cu3Bi(Se1-xTexO3)2O2Cl (0 ≤ x ≤ 1.0) series were analyzed by rietveld refinement analysis by using the software GSAS. For doping concentration x  0.6, the crystal structure changes from Pmmn to Pcmn space group. The lattice constants a and b increase, but c decreases with increasing concentration of Te doping, which indicates Te doping anisotropically expand the unit cell. However, for the case Cu3Bi (SeO3) 2O2Cl1-xBrx (0 ≤ x ≤ 1.0), the lattice constants a, b and c increases with x that signifies the isotropic expansion of unit cell. 　　The effects of pressure on the magnetic properties have been studied in Kagome Cu3Bi(Se1-xTexO3)2O2Cl (0 ≤ x ≤ 1.0) and Cu3Bi(SeO3)2O2Cl1-xBrx (0 ≤ x ≤ 1.0) polycrystalline samples. For anisotropic expansion, the antiferromagnetic transition temperature (TN) and the critical field (Hc) of metamagnetic spin-flip transition increase with Te doping. However, the value of saturation magnetization (Ms) decreases with Te doping concentration. For isotropic expansion, Ms TN and Hc shows only minute change under Br doping. The compression of unit cell by external pressure shows the TN and Ms increase, while the Hc reduces. 　　Our comprehensive studies of physical/chemical pressure indicate the anisotropic expansion shows prominent influence on the magnetic properties of Cu3Bi(SeO3)2O2Cl. This can be explained by the modulation of competition between ferrimagnetic intralayers interactions. The route to control the spin-flip transition by anisotropic pressure effects might be helpful to understand the mechanism of field-induced metamagnetic Cu3Bi(SeO3)2O2Cl.