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Magnetic clusters formation in Li1-xNi1+xO2 compounds : experiments and numerical simulations

D. Mertz, Y. Ksari, F. Celestini, J. M. Debierre, A. Stepanov, C. Delmas

cond-mat.mtrl-sciarXiv:cond-mat/9904194

Abstract

The magnetic properties of Li1-xNi1+xO2 compounds with x ranging between 0.02 and 0.2 are investigated. Magnetization and ac susceptibility measured at temperatures between 2 K and 300 K reveal a high sensitivity to x, the excess Nickel concentration. We introduce a percolation model describing the formation of Ni clusters and use an Ising model to simulate their magnetic properties. Numerical results, obtained by a Monte-Carlo technique, are compared to the experimental data. We show the existence of a critical concentration, xc = 0.136, locating the Ni percolation threshold. The system is superparamagnetic for x<xc, while it is ferrimagnetic for x>xc. The 180 Ni-O-Ni inter-plane super-exchange coupling J -110K is confirmed to be the predominant magnetic interaction. From the low temperature behavior, we find a clear indication of a 90 Ni-O-Ni intra-plane antiferromagnetic interaction J -1.5K which implies magnetic frustration.

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