Relaxing Kondo-screened Kramers doublets in CeRhSi 3

CeRhSi 3 is a superconductor under pressure coexisting with a weakly antiferromagnetic phase characterized by a Bragg peak at → q 0 = ( ∼ 0.2 , 0 , 0.5 ) [N. Aso et al., J. Magn. Magn. Mater. 310, 602 (2007)]. The compound is also a heavy-fermion material with a large specific heat coefficient γ = 110 mJ mol − 1 K − 2 and a high Kondo temperature of T K = 50 K, indicating CeRhSi 3 is in a strongly Kondo screened state. We apply high-resolution neutron spectroscopy to investigate the magnetic fluctuations in the normal phase, at ambient pressures, and at low temperatures. We measure a commensurate dynamic response centered around the → Q = ( 0 , 0 , 2 ) position that gradually evolves to H ∼ 0.2 with decreasing temperature and/or energy transfers. The response is broadened both in momentum and energy and is not reminiscent of sharp spin wave excitations found in insulating magnets where the electrons are localized. We parametrize the excitation spectrum and temperature dependence using a heuristic model utilizing the random-phase approximation to couple relaxing Ce 3 + ground-state Kramers doublets with a Kondo-like dynamic response. With a Ruderman-Kittel-Kasuya-Yosida exchange interaction within the a b plane and an increasing single-site susceptibility, we can qualitatively reproduce the neutron spectroscopic results in CeRhSi 3 and, namely, the trade-off between scattering at commensurate and incommensurate positions. We suggest that the antiferromagnetic phase in CeRhSi 3 is driven by weakly correlated relaxing localized Kramers doublets and that CeRhSi 3 at ambient pressures is on the border between a Rudderman-Kittel-Yosida antiferromagnetic state and a Kondo-screened phase where static magnetism is predominately absent.