Impurity effects at finite temperature in the two-dimensional S=1/2 Heisenberg antiferromagnet

Abstract

We discuss effects of various impurities on the magnetic susceptibility and the specific heat of the quantum S=1/2 Heisenberg antiferromagnet on a two-dimensional square lattice. For impurities with spin S_i > 0 (here S_i=1/2 in the case of a vacancy or an added spin, and S_i=1 for a spin coupled ferromagnetically to its neighbors), our quantum Monte Carlo simulations confirm a classical-like Curie susceptibility contribution S_i^2/4T, which originates from an alignment of the impurity spin with the local Néel order. In addition, we find a logarithmically divergent contribution, which we attribute to fluctuations transverse to the local Néel vector. We also study frustrated and nonfrustrated bond impurities with S_i=0. For a simple intuitive picture of the impurity problem, we discuss an effective few-spin model that can distinguish between the different impurities and reproduces the leading-order simulation data over a wide temperature range.

15 pages, 14 figures, submitted to PRB. v2, published version with cosmetic changes

References in corpus (5)

• Quantum impurity in an antiferromagnet: non-linear sigma model theory
• Quantum Magnetic Impurities in Magnetically Ordered Systems
• Susceptibility of the 2D S=1/2 Heisenberg antiferromagnet with an impurity
• Boundary susceptibility in the spin-1/2 chain: Curie like behavior without magnetic impurities
• Long Range Dynamics Related to Magnetic Impurity in the 2D Heisenberg Antiferromagnet

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