title: Solitary Magnons in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.
abstract: CaFe_{2}O_{4} is a S=5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c-axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ∼1  ns 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 ∼1-2 c-axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A+B orders as well as localization of spin excitations in a classical magnet.
authors.affiliation: School of Physics and Astronomy and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Stock
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Rodriguez
authors.affiliation: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854, USA.
authors.forename: N
authors.initials: N
authors.lastname: Lee
authors.affiliation: School of Physical Sciences, University of Kent, Canterbury CT2 7NH, United Kingdom.
authors.forename: M A
authors.initials: MA
authors.lastname: Green
authors.affiliation: ISIS Facility, Rutherford Appleton Labs, Chilton, Didcot OX11 0QX, United Kingdom.
authors.forename: F
authors.initials: F
authors.lastname: Demmel
authors.affiliation: ISIS Facility, Rutherford Appleton Labs, Chilton, Didcot OX11 0QX, United Kingdom.
authors.forename: R A
authors.initials: RA
authors.lastname: Ewings
authors.affiliation: Institute Laue-Langevin, 6 rue Jules Horowitz, Boite Postale 156, 38042 Grenoble Cedex 9, France.
authors.forename: P
authors.initials: P
authors.lastname: Fouquet
authors.affiliation: School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, United Kingdom.
authors.forename: M
authors.initials: M
authors.lastname: Laver
authors.affiliation: Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
authors.forename: Ch
authors.initials: Ch
authors.lastname: Niedermayer
authors.affiliation: Jülich Centre for Neuton Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstraße 1, D-85747 Garching, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Su
authors.affiliation: Jülich Centre for Neuton Science JCNS, Forschungszentrum Jülich GmbH, Outstation at MLZ, Lichtenbergstraße 1, D-85747 Garching, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Nemkovski
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.|Department of Materials Science, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Rodriguez-Rivera
authors.affiliation: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, 136 Frelinghuysen Road, Piscataway, New Jersey 08854, USA.
authors.forename: S-W
authors.initials: SW
authors.lastname: Cheong