TY - JOUR

T1 - A model for doping-dependent magnetic frustration and ordering in a triangular lattice

AU - Sheshadri, K.

AU - Chainani, Ashish Atma

PY - 2013/10/1

Y1 - 2013/10/1

N2 - The family of cobaltates AxCoO2 (A = Na, Li, K), with a crystal structure consisting of a layered triangular lattice of Co ions, exhibits a fascinating range of coupled spin, charge and ion ordering phenomena as a function of electron doping content x. Based on these experimental observations, we investigate an extended Ising model for suppression of magnetic frustration caused by electron doping in a quasi-2-dimensional nearest-neighbour antiferromagnetic triangular lattice. As determined by geometry and bond-counting, it is found that magnetic frustration can be quantified by a frustration index fub and its magnitude is a non-monotonic function of x. A mean-field calculation is carried out to determine the temperature-dependent magnetization, spin-entropy and heat capacity for the obtained structures with the lowest energy (≡ lowest fub) for each x. The calculations reveal that the magnetic-ordering temperature TC exhibits an anti-correlation with fub as a function of x. In addition, as seen in thermopower experiments, an anomalous spin-entropy is obtained for the high-doping cases when . The results indicate the importance of doping-dependent magnetic frustration in the layered cobaltates.

AB - The family of cobaltates AxCoO2 (A = Na, Li, K), with a crystal structure consisting of a layered triangular lattice of Co ions, exhibits a fascinating range of coupled spin, charge and ion ordering phenomena as a function of electron doping content x. Based on these experimental observations, we investigate an extended Ising model for suppression of magnetic frustration caused by electron doping in a quasi-2-dimensional nearest-neighbour antiferromagnetic triangular lattice. As determined by geometry and bond-counting, it is found that magnetic frustration can be quantified by a frustration index fub and its magnitude is a non-monotonic function of x. A mean-field calculation is carried out to determine the temperature-dependent magnetization, spin-entropy and heat capacity for the obtained structures with the lowest energy (≡ lowest fub) for each x. The calculations reveal that the magnetic-ordering temperature TC exhibits an anti-correlation with fub as a function of x. In addition, as seen in thermopower experiments, an anomalous spin-entropy is obtained for the high-doping cases when . The results indicate the importance of doping-dependent magnetic frustration in the layered cobaltates.

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U2 - 10.1209/0295-5075/104/27007

DO - 10.1209/0295-5075/104/27007

M3 - Article

AN - SCOPUS:84888591005

VL - 104

JO - Europhysics Letters

JF - Europhysics Letters

SN - 0295-5075

IS - 2

M1 - 27007

ER -