Multiphase Competition In The Quantum Xy Pyrochlore Antiferromagnet Cdyb2se4: Zero And Applied Magnetic Field Study

We study magnetic behavior of the Yb3+ ions on a frustrated pyrochlore lattice in the spinel CdYb2Se4. The crystal-electric-field parameters deduced from high-energy inelastic neutron scattering reveal a well-isolated ytterbium ground-state doublet with a weakly Ising character. Magnetic order studied by powder neutron diffraction evolves from the XY-type antiferromagnetic Gamma(5) state to a splayed icelike ferromagnet (both with k = 0) in applied magnetic field with B-c = 3 T. Low-energy inelastic neutron scattering identifies weakly dispersive magnetic bands around 0.72 meV starting at vertical bar Q vertical bar = 1.1 angstrom(-1) at zero field, which diminish with field and vanish above 3 T. We explain the observed magnetic behavior in framework of the nearest-neighbor anisotropic exchange model for effective S = 1/2 Kramers doublets on the pyrochlore lattice. The estimated exchanges position the CdYb2Se4 spinel close to the phase boundary between the Gamma(5) and splayed ferromagnet states, similar to the Yb pyrochlores, suggesting an important role of the competition between these phases.