Ferromagnetism within the Periodic Anderson Model: A New Approximation Scheme

Abstract

We introduce a new approach to the periodic Anderson model (PAM) that allows a detailed investigation of the magnetic properties in the Kondo as well as the intermediate valence regime. Our method is based on an exact mapping of the PAM onto an effective medium strong-coupling Hubbard model. For the latter, the so-called spectral density approach (SDA) is rather well motivated since it is based on exact results in the strong coupling limit. Besides the T 0 phase diagram, magnetization curves and Curie temperatures are presented and discussed with help of temperature-dependent quasiparticle densities of state. In the intermediate valence regime, the hybridization gap plays a major role in determining the magnetic behaviour. Furthermore, our results indicate that ferromagnetism in this parameter regime is not induced by an effective spin±spin interaction between the localized levels mediated by conduction electrons as it is the case in the Kondo regime. The magnetic ordering is rather a single-band effect within an effective f-band.

Ferromagnetism in the periodic Anderson model. A comparison of spectral density approximation (SDA), modified alloy analogy (MAA) and modified perturbation theory (MPT)

“…In these papers, the SDA was applied to a set of effective Hubbard models, onto which the PAM could be mapped. However, the above-described procedure leads to exactly the same results as those published in references [6,7] …”

“…Results for the SDA in the context of the PAM were previously published [6,7]. In these papers, the SDA was applied to a set of effective Hubbard models, onto which the PAM could be mapped.…”

Ferromagnetism in the two-dimensional periodic Anderson model

“…For 18 and 26 electrons, the energy per site either does not vary within statistical error or increases. For 20,22, and 24 electrons, it has a clear minimum but the minimum for 24 electrons is just barely below unity. We note that the minimum in energy and the maximum in S z occurs for a half-filled conduction electron shell.…”

“…Ferromagnetism seems to be readily found by meanfiled approximations in any dimensions [16][17][18][19][20][21][22]. Using a slave-boson mean-field theory (SBMFT) for the symmetric PAM, Möller and Wölfe [16] found results similar to those of Noack and Guerrero.…”

“…At 3/8 filling they proposed a specific Kondoinduced mechanism for ferromagnetism that has the conduction electrons in a spin-polarized charge density-wave anti-aligned with the ferromagnetically aligned local moments on the valence orbitals. More recently Meyer and Nolting [20][21][22] appended perturbation theory to DMFT and also predicted ferromagnetism over a broad ramge of electron filling extending below 1/4 filling.…”