Solitary magnons in the $S=\frac{5}{2}$ antiferromagnet CaFe${}_2$O${}_4$

Abstract

CaFe${}_2$O${}_4$ is a $S=\frac{5}{2}$ anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A ($\uparrow \uparrow \downarrow \downarrow$) and B ($\uparrow \downarrow \uparrow \downarrow$) 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 results in magnetic antiphase boundaries along $c$ which freeze on the timescale of $\sim$ 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 $\sim$ 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.

arXiv comment(main text - 5 pages, 4 figures; supplementary information - 2 pages, 1 figure, to be published in Physical Review Letters)

References in corpus (13)

• Discrete Breathers
• Solitons in nonlinear lattices
• Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry
• Electronic States and Magnetic Propertis of Edge-sharing Cu-O Chains
• A hierarchy of bound states in the 1D ferromagnetic Ising chain CoNb${}_2$O${}_6$ investigated by high resolution time-domain terahertz spectroscopy
• One-dimensional magnetic fluctuations in the spin-2 triangular lattice α-NaMnO2
• Spin Susceptibility and Superexchange Interaction in the Antiferromagnet CuO
• Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K)
• Incommensurate short-range order in the S=1 triangular antiferromagnet NiGa2S4
• Spin dynamics near the critical doping in weakly-superconducting underdoped YBa2Cu3O6.35 (Tc=18K)
• Dynamic scaling in spin glasses
• Spin Fluctuations from Hertz to Terahertz on a Triangular Lattice
• Counting discrete emission steps from intrinsic localized modes in a quasi-1D antiferromagnetic lattice

Cited by in corpus (10)

• Upgrade to the MAPS neutron time-of-flight chopper spectrometer
• Structure and magnetic properties of epitaxial CaFe2O4 thin films
• Evidence for the Confinement of Magnetic Monopoles in Quantum Spin Ice
• Orphan spins and bound in-gap states in the $S=\frac{5}{2}$ antiferromagnet CaFe${}_2$O${}_4$
• Metastable antiphase boundary ordering in CaFe${}_2$O${}_4$
• From one- to two-magnon excitations in the S=3/2 magnet $\beta$-CaCr${}_2$O${}_4$
• Energy thresholds of discrete breathers in thermal equilibrium and relaxation processes
• Non-linear soliton confinement in weakly coupled antiferromagnetic spin chains
• Metastable and localized Ising magnetism in $\alpha$-CoV${}_2$O${}_6$ magnetization plateaus
• Unusual ferrimagnetism in CaFe2O4