Framework Of Periodic Anderson Model Research Articles

K- and spin-dependent hybridization effects in Ce monolayer

Here we present applications of the periodic Anderson model (PAM) to consideration of wave vector (k)- and spin-dependent hybridization effects in Ce metal. It was shown that k-dependent splitting of the 4f ionization peak of Ce/W(1 10) are correctly described in the framework of the PAM (Coulomb repulsion between two f electrons localized on the same lattice site Uff→∞). Our results show that the wave vector is conserved upon hybridization. In case of the magnetically ordered Ce monolayer, spin- and angle-resolved resonant photoemission spectra reveal spin-dependent changes of the Fermi-level peak intensities (which reflect the hybridization strength). That indicate a spin-dependence of 4f hybridization and, thus, of 4f occupancy and local moment. The phenomenon was also described in the framework of PAM by 4f electron hopping into the exchange split Fe 3d derived bands that form a spin-gap at the Fermi energy around the T point of the surface Brillouin zone.

Interface defects and formation of non-collinear magnetic ordering in Fe/Cr multilayers

Non-collinear magnetic structure of Fe/Cr multilayers was investigated within the framework of Periodic Anderson model (PAM) in mean field approximation for Coulomb repulsion on sites. Self-consistent calculations were performed for the superlattices with different step width at the interface. It is shown that due to frustration in the interface region the ground state corresponds to non-collinear orientation of magnetic moments near steps. This non-collinear ordering penetrates on a large distance from the interface both in Fe and Cr layers and leads to the non-collinear magnetic coupling between Fe layers through the Cr spacer. Angle between magnetic moments of Fe slabs depends strongly not only on the thickness of the Cr spacer but also on the interface structure at atomic scale. It is found that only very specific types of the interface defects with plural frustrations can give out-of-plane orientation of magnetic moments.

MAGNETIC PROPERTIES OF BINARY DISORDERED ALLOY

A model binary alloy Ax B1−x where A and B represent ferromagnetic and paramagnetic transition metal respectively is considered within the framework of periodic Anderson model, and the effects of d-level disorder and variation of electron concentration due to alloying on the magnetic properties are investigated. The phase boundary, thermal behavior of magnetization and susceptibility of the alloy are obtained using HF approximation for the Coulomb interaction and the virtual crystal approximation for d-level disorder. The ferromagnetic state of alloy vanishes at a critical concentration xc which depends on d-band width, strength of s-d hybridization and the Coulomb interaction. The re-entrant magnetic phase is found within a small region of x for alloy with narrow d-band. For x≲xc, the magnetic properties resemble that of spin-glass system. For x≪xc, the alloy behaves like a Pauli paramagnet. The re-entrant and spin-glass-like phases are associated with the increase in d-level population as temperature decreases. Local moment for x≃1 decreases with temperature up to Tc whereas the reverse is the situation for alloy exhibiting spin-glass-like behavior.