  The interplay between competing degrees of freedom can stabilize non-trivial
magnetic states in correlated electron materials. Frustration-induced strong
quantum fluctuations can evade long-range magnetic ordering leading to exotic
quantum states such as spin liquids in two-dimensional spin-lattices such as
triangular and kagome structures. However, the experimental realization of
dynamic and correlated quantum states is rare in three-dimensional (3D)
frustrated magnets wherein quantum fluctuations are less prominent. Herein, we
report the crystal structure, magnetic susceptibility, electron spin resonance
(ESR) and specific heat studies accompanied by crystal electric field (CEF)
calculations on a 3D frustrated magnet Yb3Sc2Ga3O12. In this material, Yb3+
ions form a three-dimensional network of corner-sharing triangles known as
hyperkagome lattice without any detectable anti-site disorder. Our results
reveal a low energy state with Jeff = 1/2 degrees of freedom in the Kramers
doublet state. The zero field-cooled and field cooled magnetic susceptibility
taken in 0.001 T rules out the presence of spin-freezing down to 1.8K. The
Curie-Weiss (CW) fit to low-T susceptibility data yields a small and negative
CW temperature indicating the presence of a weak antiferromagnetic interaction
between Jeff = 1/2 (Yb3+) moments. The Yb-ESR displays a broad line of
non-Lorentzian shape that suggests considerable magnetic anisotropy in
Yb3Sc2Ga3O12. The CEF calculations suggest that the ground state is well
separated from the excited states, which are in good agreement with
experimental results. The absence of long-range magnetic ordering indicates a
dynamic liquid-like ground state at least down to 130 mK. Furthermore, zero
field specific heat shows a broad maximum around 200 mK suggesting the presence
of short-range spin correlations in this 3D frustrated antiferromagnet.
