Magnitude of the Magnetic Exchange Interaction in the Heavy-Fermion Antiferromagnet CeRhIn5

We have used high-resolution neutron spectroscopy experiments to determine the complete spin wave spectrum of the heavy-fermion antiferromagnet CeRhIn5. The spin wave dispersion can be quantitatively reproduced with a simple frustrated J1-J2 model that also naturally explains the magnetic spin-spiral ground state of CeRhlnS and yields a dominant in-plane nearest-neighbor magnetic exchange constant J0=0.74(3) meV. Our results pave the way to a quantitative understanding of the rich low-temperature phase diagram of the prominent CeTln5 (T=Co, Rh, Ir) class of heavy-fermion materials.