Eur. Phys. J. B 58, 389-393 (2007)
https://doi.org/10.1140/epjb/e2007-00245-9

Extended spin waves in aperiodic ferromagnetic chains

Instituto de Física, Universidade Federal de Alagoas, Maceió AL, 57072-970, Brazil

Corresponding author: ^a fidelis@if.ufal.br

Received: 13 November 2006
Revised: 7 August 2007
Published online: 22 September 2007

Abstract

In this work, a one-dimensional quantum Heisenberg ferromagnet with aperiodic exchange couplings is considered. To produce an aperiodic distribution of exchange couplings, it is used a sinusoidal function whose phase φ varies as a power-law, φ∝n^ν, where n labels the positions along the chain. By using exact diagonalization, the spin-wave participation number and the local density of states are computed. The numerical calculations indicate that for 0 < ν < 1, this ferromagnetic system displays a phase of extended spin waves in the low-energy region. For ν > 1 all spin waves are localized except for the zero energy mode. By integrating the time-dependent Schrödinger equation, the temporal evolution of the mean-square displacement of the wave-packet was followed. Associated with the emergence of extended spin waves, it was observed that the wave-packet mean-square displacement displays a ballistic spread.