We have developed an underscreened Kondo lattice model with an intra-site Kondo exchange interaction JK between the conduction band and localized 5f electrons-described by S = 1 spins in the f2 configuration-and an inter-site ferromagnetic exchange f-f interaction JH. Using a fermionic representation for the spin operators and a mean-field approximation we obtain, from T = 0 up to a critical temperature, a Kondo-ferromagnetic coexistence. This is in agreement with the experimental situation of some Uranium compounds, such as UTe or UCu0.9 Sb2, which order ferromagnetically with a Curie temperature of order 100 K and present also a Kondo behavior. The Curie and Kondo temperatures are also determined.
Bibliographical noteFunding Information:
This work was partially supported by Brazilian agencies CNPq and FAPERGS through PRONEX 04/0874.9. JRI thanks the hospitality of LPS, Orsay, France, and MPIPKS, Dresden, Germany, and NBP thanks FAPERGS for support during her stay at IF-UFRGS, Porto Alegre, Brazil.
- Kondo lattice
- Underscreened Kondo model
- Uranium compounds