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CaFe₂O₄ is a S=5/2 anisotropic antiferromagnet based on 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 [1]. We apply neutron scattering to demonstrate that the competing orders result in magnetic antiphase boundaries separating these two order parameters at low temperatures. Neutron diffraction and bulk susceptibility find that the spins near these boundaries are weakly correlated and carry an uncompensated moment. Using high resolution neutron spectroscopy, we find that these boundaries are confining and measure a series of 9 quantized spin wave levels at low temperatures [2]. The competing anisotropic order parameters affords both localization of spin waves and also orphan spins in a classical magnet.
[1] L. M. Corliss et al. Phys. Rev. 160, 408 (1967).
[2] C. Stock et al. Phys. Rev. Lett. 117, 017201 (2016).