School of Physics and Astronomy

Stripes, antiphase boundaries, and solitary magnons in Harmunite

19 April 2016

Time: 2:00pm
Venue: GO Jones Room 610

Series: 
CCMMP Seminars
Speaker: 
Chris Stock
Host: 
Martin Dove
 
Abstract: 

Harmunite is the mineral form of CaFe2O4 which is a S=5/2 anisotropic antiferromagnetic based upon zig-zag chains having two competing magnetic structures that differ by the c-axis stacking of ferromagnetic stripes.  We apply neutron scattering to demonstrate that the competing order parameters results in magnetic antiphase boundaries which freeze on the nanosecond timescale at the onset of magnetic order at 200 K.  Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions of a few unit cells in size.  We discuss these in the context of solitary magnons predicted to exist in anisotropic systems and previously observed through optically driving large amplitude spin waves.  The magnetic anisotropy affords both competing magnetic orders as well as localization of spin excitations in a classical magnet.