Stabilization ofd-band ferromagnetism by hybridization with uncorrelated bands

Abstract

We investigate the influence of s-d or p-d hybridization to d-band ferromagnetism to estimate the importance of hybridization for the magnetic properties of transition metals. To focus our attention to the interplay between hybridization and correlation we investigate a simple model system consisting of two non-degenerated hybridized bands, one strongly correlated, the other one quasi-free. To solve this extended Hubbard model, we apply simple approximations, namely SDA and MAA, that, concerning ferromagnetism in the single-band model, are known to give qualitatively satisfactory results. This approach allows us to discuss the underlying mechanism, by which dband ferromagnetism is influenced by the hybridization on the basis of analytical expressions. The latter clearly display the order and the functional dependencies of the important effects. It is found, that spin-dependent inter-band particle fluctuations cause a spin-dependent band shift and a spin-dependent band broadening of the Hubbard bands. The shift stabilizes, the broadening tends to destabilize ferromagnetism. Stabilization requires relatively high band distances and small hybridization matrix elements. Super-exchange and RKKY coupling are of minor importance.

Evolution of stress and magnetism during the first-order phase transition of MnAs/GaAs(001)

“…The coupling between the localized d-states of Mn and p-or d-states of As, already deemed responsible by older double-exchange theory [10], indeed drives the transition from the paramagnetic to the ferromagnetic state. This is confirmed by density functional theory [11] and a recent two-band Hubbard-model study claiming that a small change in p-d hybridization can give a 'final kick' to a system that is close to a ferromagnetic transition [12]. …”

Ferromagnetism in two band metals: The very strong coupling limit

“…We want now to exhibit the combined effect of V , α and s on this process at T = 0K, for each n tot . Schwieger and Nolting [3] address to the same problem using methods similar to ours, the Spectral density approach (SDA) and the Modified Alloy analogy (MAA) both giving rise to a band shift. There are nevertheless some differences: their methods do not arrive at a self-consistency equation so they make an expansion in V and 1 w and find the self-energy analytically in some approximation.…”

“…Magnetism in itinerant ferromagnets still attracts great interest [1][2][3][4][5][6][7][8][9][10][11]. It is then relevant to propose, use and test models on this subject and analyze their effectiveness, what we do in this paper for a specific model.…”

Ferromagnetism in two band metals: Combined effect of Coulomb correlation, hybridization and band widths

“…Bernhard [2] addresses the correlated one-band problem, while Schwieger and Nolting [3] treats also a hybridized twoband model using the spectral density approach (SDA) and a modified alloy analogy. Their approach is equivalent to the socalled Hubbard I [5] while ours is equivalent rather to Hubbard III [6].…”