Europhys. Lett., 61 (6) , pp. 838-844 (2003)
Size-dependent magnon modes of a Heisenberg ferromagnetS. Cojocaru1, 2 and A. Ceulemans1
1 Division of Quantum Chemistry, University of Leuven Celestijnenlaan 200F, B-3001 Leuven, Belgium
2 Institute of Applied Physics - Chisinau, Moldova
(Received 21 May 2002; accepted 9 January 2003)
We prove the existence of new bound magnon excitations in Heisenberg ferromagnets due to finite-size effects. To describe these effects, we develop an analytical approximation which is a modification of the widely used continuum approach. Thus, for the square lattice we find 4 branches of bound two-magnon excitations in addition to the two ones known before. It is shown that some of the new modes remain well separated from all the others even for a macroscopic system.
75.10.Jm - Quantized spin models.
75.30.Ds - Spin waves.
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