Ferromagnetism and phase separation in one-dimensional d-p and periodic Anderson models

Using the Density Matrix Renormalization Group, we study metallic ferromagnetism in a one-dimensional copper-oxide model which contains one oxygen p-orbital and one copper d-orbital. The parameters for the d-p model can be chosen so that it is similar to the one-dimensional periodic Anderson model. For these parameters, we compare the ground-state phase diagram with that of the Anderson model and find a ferromagnetic region analogous to one found in the Anderson model, but which is pushed to somewhat higher densities and interaction strengths. In both models, we find a region within the ferromagnetic phase in which phase separation between a localized ferromagnetic domain and a weakly antiferromagnetic regime occurs. We then choose a set of parameter values appropriate for copper-oxide materials and explore the ground-state phase diagram as a function of the oxygen-oxygen hopping strength and the electron density. We find three disconnected regions of metallic ferromagnetism and give physical pictures of the three different mechanisms for ferromagnetism in these phases.