Dresden 2014 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 37: Spin Torque and Spin Excitations I
MA 37.4: Vortrag
Donnerstag, 3. April 2014, 10:15–10:30, HSZ 401
Spin dynamics and magnon lifetime close to the percolation in two dimensional diluted magnetic systems — •Akash Chakraborty1, Paul Wenk1, John Schliemann1, and Georges Bouzerar2 — 1Institut I - Theoretische Physik, Universität Regensburg, 93040 Regensburg, Germany — 2Institut Lumiere Matiere, Universite Lyon 1-CNRS, 69622 Villeurbanne Cedex, France
Spin-wave excitations in disordered magnetic systems have been widely studied for several decades now. However, a careful search reveals a longstanding controversy on one important aspect, which is the wave- vector dependence of the spin-wave intrinsic linewidth. Different theories have predicted this dependence to be as varied as q3 to q7, but no general agreement has prevailed till now. We present here a detailed analysis of the low-temperature spin-wave excitations in two-dimensional diluted ferromagnetic systems and show that in the long wavelength limit the linewidth is in fact proportional to q4. This is in good agreement with some previous theoretical studies which predicted a qd+2dependence (d is the dimensionality). One of the primary difficulties in extracting the correct wave-vector dependence is the fact that this q4 behavior holds only for very small q-values, in a restricted region of the Brillouin zone. This possibly explains the failure to observe this behavior experimentally, as it is considerably difficult to probe such small wave-vectors. In addition, we show that evaluating the linewidth from the moments associated with the spectral density leads to an incorrect linear dependence in q.