Helimagnons in a chiral ground state of the pyrochlore antiferromagnets
1 Department of Physics, University of Wisconsin - Madison, WI 53706, USA
2 Theoretical Division, Los Alamos National Laboratory - Los Alamos, NM 87545, USA
Received: 13 December 2012
Accepted: 23 January 2013
The Goldstone mode in a helical magnetic phase, also known as the helimagnon, is a propagating mode with a highly anisotropic dispersion relation. Here we study theoretically the magnetic excitations in a complex chiral ground state of pyrochlore antiferromagnets such as spinel CdCr2O4 and itinerant magnet YMn2. We show that the effective theory of the soft modes in the helical state possesses a symmetry similar to that of smectic liquid crystals. An overall agreement is obtained between experiments and our dynamics simulations with realistic model parameters. By exactly diagonalizing the linearized Landu-Lifshitz equation in various commensurate limits of the spiral order, we find a low-energy dispersion relation characteristic of the helimagnons. Our calculation thus reveals the first example of helimagnon excitations in geometrically frustrated spin systems.
PACS: 75.10.Hk – Classical spin models / 75.30.Ds – Spin waves / 75.47.Lx – Magnetic oxides
© EPLA, 2013