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The European Physical Journal B
ISSN: 1434-6028 (printed version)
ISSN: 1434-6036 (electronic version)
Abstract Volume 3 Issue 1 (1998) pp 35-40
Macroscopic quantum coherence of the Neel vector in antiferromagnetic system without Kramers' degeneracy
R. Lü (a), J.-L. Zhu, X. Chen, L. Chang
Department of Physics, Tsinghua University, Beijing, 100084, P.R. China
Received: 24 July 1997 / Accepted: 30 September 1997
Abstract: At low temperatures the Neel vector in a small antiferromagnetic particle can possess quantum coherence between the classically degenerate minima. In some cases, the topological term in the magnetic action can lead to destructive interference between the symmetry-related trajectories for the half-integer excess spin antiferromagnetic particle. By studying a macroscopic quantum coherence problem of the Neel vector with biaxial crystal symmetry and a weak magnetic field applied along the hard axis, we find that the quenching of tunnel splitting could take place in the system without Kramers' degeneracy. Both the Wentzel-Kramers-Brillouin exponent and the pre-exponential factors are found exactly for the tunnel splitting. Results show that the tunnel splitting oscillates with the weak applied magnetic field for both the integer and half-integer excess spin antiferromagnetic particles, and vanishes at certain values of the field. All the calculations are performed based on the two sublattices model and the instanton method in spin-coherent-state path integral.
PACS. 75.10.Jm Quantized spin models - 73.40.Gk Tunneling - 75.50.Ee Antiferromagnetics
(a) email: rlu@Phys.Tsinghua.edu.cn
Article in PDF-Format (258 KB)
Online publication: June 22, 1998
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