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Magnetic phases of the mixed-spin $J_1-J_2$ Heisenberg model on a square lattice

N. B. Ivanov·J. Richter·D. J. J. Farnell
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Abstract

We study the zero-temperature phase diagram and the low-energy excitations of a mixed-spin ($S_1>S_2$) $J_1-J_2$ Heisenberg model defined on a square lattice by using a spin-wave analysis, the coupled cluster method, and the Lanczos exact-diagonalization technique. As a function of the frustration parameter $J_2/J_1$ ($ >0$), the phase diagram exhibits a quantized ferrimagnetic phase, a canted spin phase, and a mixed-spin collinear phase. The presented results point towards a strong disordering effect of the frustration and quantum spin fluctuations in the vicinity of the classical spin-flop transition. In the extreme quantum system $(S_1,S_2)=(1,{1/2})$, we find indications of a new quantum spin state in the region $0.46< J_2/J_1<0.5$

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N. B. Ivanov, J. Richter, D. J. J. Farnell. 2002-07-10. Magnetic phases of the mixed-spin $J_1-J_2$ Heisenberg model on a square lattice. https://doi.org/10.1103/physrevb.66.014421

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