The competition between Kondo screening and indirect magnetic exchange is studied for a system with geometrical frustration using dynamical mean-field theory (DMFT). We systematically scan the weak- to strong-coupling regime of the periodic Anderson model on the triangular lattice for a wide range of fillings $n$. The magnetic phase diagram is derived using a site-dependent DMFT approach by self-consistent mapping onto three independent single-impurity models corresponding to the three correlated $f$ orbitals in the unit cell. At half-filling, the system is a nonmagnetic Kondo insulator for all considered interaction strengths $U>0$, which immediately develops into a nonmagnetic metallic Kondo-singlet phase for fillings slightly below half-filling. On the other hand, indirect magnetic exchange between the $f$ moments results in antiferromagnetic order at lower fillings. The antiferromagnetic and Kondo-singlet phases are separated in the $U\text{−}n$ phase diagram by an extended region of partial Kondo screening, i.e., a phase in which the magnetic moment at one site in the unit cell is Kondo-screened while the remaining two are coupled antiferromagnetically. At even lower fillings, the system crosses over from a local-moment to a mixed-valence regime in which the minimization of the kinetic energy in a strongly correlated system gives rise to a metallic and partially polarized ferromagnetic state.

• Received 19 June 2015
• Revised 27 November 2015

DOI:https://doi.org/10.1103/PhysRevB.92.235131