Ligand dependent magnetism of theJeff= 3/2 Mott insulator Cs2MX6(M= Ta, Nb,X= Br, Cl)
Hajime Ishikawa1, Takeshi Yajima1, Akira Matsuo1
1Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, Japan.
Abstract:
Magnetic and structural properties of double perovskite type bromides Cs2MBr6(M= Ta, Nb), where Ta4+(5d1) and Nb4+(4d1) ions form the face centered cubic lattice, are investigated and compared with chlorides Cs2MCl6. Cs2TaBr6exhibits the effective magnetic moment of 0.24μB, which is much smaller than the spin only value of ad1ion, 1.73μB, and comparable to 0.25μBin Cs2TaCl6. On the other hand, the effective magnetic moment of Cs2NbBr6is 0.7μBand is substantially smaller than 1.0μBin Cs2NbCl6. On cooling, successive structural and magnetic phase transitions accompanying the release of electronic entropy approximatelyRln 4 in total as expected for theJeff= 3/2 state are observed. The type of the ligand changes the temperature dependence of magnetic susceptibility at low temperature as well as its magnitude. The role of the ligands on the magnetism ofJeff= 3/2 Mott insulators are discussed in the light of metal-ligand hybridization and the electron-lattice coupling.
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