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Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO4 detected by 31P and 7Li nuclear magnetic resonance
S.H. Baek, R. Klingeler, C. Neef, C. Koo, B. Büchner and H.J. Grafe
We report 31P and 7Li nuclear magnetic resonance (NMR) studies in new non-olivine LiZnPO4-type LiCoPO4tetra microcrystals, where the Co2+ ions are tetrahedrally coordinated. Olivine LiCoPO4, which was directly transformed from LiCoPO4tetra by an annealing process, was also studied and compared. The uniform
bulk magnetic susceptibility and the 31P Knight shift obey the Curie-Weiss law for both materials with a high spin Co2+ (3d7, S = 3/2), but theWeiss temperature and the effective magnetic moment μeff are considerably smaller in LiCoPO4tetra. The spin-lattice relaxation rate T1−1 reveals a quite different nature of the spin dynamics in the paramagnetic state of both materials. Our NMR results imply that strong geometrical spin frustration
occurs in tetrahedrally coordinated LiCoPO4, which may lead to the incommensurate magnetic ordering.
Phys. Rev. B 89, 134424 (2014)
doi: 10.1103/PhysRevB.89.134424