We study magnetic behaviour of the Yb3+ ions on a frustrated pyrochlore lattice in the spinel {\CYS}. The crystal-electric field parameters deduced from high-energy inelastic neutron scattering reveal well-isolated ytterbium ground state doublet with a weakly Ising character. Magnetic order studied by powder neutron diffraction evolves from the XY-type antiferromagnetic Γ5 state to a splayed ice-like ferromagnet (both with k=0) in applied magnetic field with Bc=3 T. Low-energy inelastic neutron scattering identifies weakly dispersive magnetic bands around 0.72 meV starting at ∣Q∣ = 1.1 \AA−1~ at zero field, which diminish with field and vanish above 3 T. We explain the observed magnetic behaviour in framework of the nearest-neighbour anisotropic exchange model for effective S=1/2 Kramers doublets on the pyrochlore lattice. The estimated exchanges position the {\CYS} spinel close to the phase boundary between the Γ5 and splayed ferromagnet states, similar to the Yb-pyrochlores suggesting an important role of the competition between these phases.
@article{arxiv.1908.09510,
title = {Multi-phase competition in quantum $XY$ pyrochlore antiferromagnet CdYb$_{2}$Se$_{4}$: zero and applied magnetic field study},
author = {K. Guratinder and Jeffrey G. Rau and V. Tsurkan and C. Ritter and J. Embs and T. Fennell and H. C. Walker and M. Medarde and T. Shang and A. Cervellino and Ch. Rüegg and O. Zaharko},
journal= {arXiv preprint arXiv:1908.09510},
year = {2019}
}