Magnetic phases in the correlated Kondo-lattice model

We study magnetic ordering of an extended Kondo-lattice model including an additional on-site Coulomb interaction between the itinerant states. The model is solved in the dynamical mean-field theory using the numerical renormalization group approach of Wilson and coworkers [Phys. Rev. B 21, 1003 (1980); Rev. Mod. Phys. 47, 773 (1975); R. Bulla, et al., arXiv:cond-mat/0701105 (unpublished)] as impurity solver. For a bipartite lattice, we find at half-filling the expected antiferromagnetic phase. Upon doping, this phase is gradually suppressed and hints toward phase separation are observed. For large doping, the model exhibits ferromagnetism, the appearance of which can, at first sight, be explained by the Ruderman-Kittel-Kasuya-Yosida interaction. However, for large values of the Kondo coupling $J$, significant differences from a simple Ruderman-Kittel-Kasuya-Yosida picture can be found. We, furthermore, observe signs of quantum critical points for antiferromagnetic Kondo coupling between the local spins and band states.

Figure 1

${\phantom{\mid }\frac{d}{dx}{\chi }^{zz}\left(x\right)\mid }_{x=0}$ for $U=0$ as function of the occupancy $n$.

Figure 2

(Color online) Antiferromagnetic polarization at half-filling and $T=0$ as function of the coupling $J$ between spins and band electrons. Circles were calculated for $U∕W=1∕200$, corresponding approximately to $U=0$; squares for $U=W$.

Figure 3

(Color online) Spectral function for the majority spin at half-filling for $U∕W=1∕200$ and temperature $T∕W=2.3\times {10}^{-4}$.

Figure 4

(Color online) Magnetic phase diagrams for $U=0$ and $\mid J\mid =W∕2$ as function of filling and temperature. The upper (lower) panel shows the results for ferromagnetic (antiferromagnetic) coupling. Lines are meant as a guide for the eyes. For ferromagnetic coupling, a magnetic phase exists between $0.45<n<0.7$, whose nature could not be determined (see text). The number of states kept during NRG calculation was increased at phase boundaries.

Figure 5

(Color online) Occupancy (upper panel) and polarization (lower panel) for the antiferromagnetic solution around half-filling as a function of chemical potential $\mu$ for different temperatures. Other parameters as in Fig. 4.

Figure 6

(Color online) Polarization of the ferromagnetic solutions. The upper (lower) panel corresponds to ferromagnetic (antiferromagnetic) coupling. Other parameters as in Fig. 4.

Figure 7

(Color online) Magnetic phase diagrams for $U=W∕2$ and $\mid J\mid =W∕2$ as a function of filling and temperature. The upper (lower) panel shows results for ferromagnetic (antiferromagnetic) coupling. Lines are meant as guides for the eye. For ferromagnetic coupling, a magnetic phase exists between $0.5<n<0.8$, whose nature could not be determined (see text). The number of states kept during NRG calculation was increased at phase boundaries.

Figure 8

(Color online) Occupancy (upper panel) and polarization (lower panel) for the antiferromagnetic solution around half-filling as a function of chemical potential $\mu$ for different temperatures. Other parameters as in Fig. 7.

Figure 9

(Color online) Polarization of the ferromagnetic solutions. The upper (lower) panel corresponds to ferromagnetic (antiferromagnetic) coupling. Other parameters as in Fig. 7.

Figure 10

(Color online) Density of states for $n=0.6$, $T=4\times {10}^{-5}$, $U=0$, $W∕2$, and $J=\pm W∕2$.