Local investigation of the crystal electric field ground-state in CeCu(Sb,Bi)$_2$ heavy fermions

In this work, we performed systematic Nuclear Magnetic Resonance (NMR) and magnetic susceptibility experiments in CeCuSb _2 2 single-crystals. The main findings were compared to previous report for CeCuBi _2 2 . The NMR spectra and transferred hyperfine coupling for the ^{63} 63 Cu nuclei were obtained aiming to observe their correlation with the crystal electric field (CEF) effects on the Ce ^{3+} 3 + ( J=5/2 J = 5 / 2 ) multiplet. Besides, in an attempt to elucidate the magnetic structure through NMR measurements at different magnetic fields orientations, we observed a magnetic transition at T\approx 8\, T ≈ 8 K higher than the Néel temperature T_N T N measured by magnetic susceptibility indicating the development of short-range magnetic ordering above T _N N . In addition, the wipe out of the main NMR resonance line and a persistent spin-echo signal throughout the whole frequency-swept range suggest the possibility of an incommensurate magnetic structure in CeCuSb _2 2 . Furthermore, the small transferred hyperfine coupling constant found for CeCuSb _2 2 indicates a scenario with more localized Ce ^{3+} 3 + 4f electrons than for CeMIn _5 5 (M = = Co,Rh,Ir) heavy fermions family. Additionally, subtle changes in the hybridization between the ^{63} 63 Cu with the 4f ^1 1 Ce ^{3+} 3 + electrons in distinct magnetic field orientations allowed us to provide detailed information and map out the 4f CEF orbital ground-state of CeCu(Sb,Bi) _2 2 via NMR measurements.