High-Field Multi-Frequency ESR in the Rare-Earth Spinel Compound CdYbS.

We have performed electron spin resonance (ESR) measurements in the low temperature magnetic-ordered state of polycrystalline samples of CdYbS. This material is one of the rare-earth spinel compounds in which Yb ions form the pyrochlore lattice, and consequently, CdYbS possesses anomalous properties caused by geometrical frustration and anisotropic terms. Some ESR signals have been detected, and their resonance fields are well-fitted by linear lines in the frequency vs. magnetic-field plane. One of the ESR modes appears to intersect the origin of this plane, suggesting a nearly gapless feature in the magnetically ordered state of this material. Two additional ESR modes appear above H = 2.6 T, indicating that there is a field-induced phase transition at H. Given the nearly gapless feature of CdYbS, we expect that the ground state of CdYbS must be either the Palmer-Chalker state or the ψ state. [ABSTRACT FROM AUTHOR]