Multi-phase competition in quantum $XY$ pyrochlore antiferromagnet CdYb$_{2}$Se$_{4}$: zero and applied magnetic field study

TL;DR

This study investigates the magnetic phases of the Yb$^{3+}$ ions in the frustrated pyrochlore lattice of CdYb$_{2}$Se$_{4}$, revealing a competition between different magnetic states influenced by external magnetic fields.

Contribution

It provides a detailed experimental and theoretical analysis of the magnetic phase competition in a Yb-based pyrochlore spinel, highlighting the role of anisotropic exchange interactions.

Findings

Magnetic order transitions from $ ext{XY}$-type antiferromagnet to splayed ice-like ferromagnet with applied field.

Weakly dispersive magnetic bands observed at zero field diminish and vanish above 3 T.

The system is close to a phase boundary between $ ext{Γ}_5$ and splayed ferromagnet states, indicating phase competition.

Abstract

We study magnetic behaviour of the Yb$^{3+}$ 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 $\Gamma_5$ state to a splayed ice-like 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 $\mid\bf{Q}\mid$ = 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 $\Gamma_5$ and splayed ferromagnet states, similar to the Yb-pyrochlores suggesting an important role of the competition between these phases.