The spatial inhomogeneity in manganites has been clearly demonstrated by inelastic neutron scattering. There is a wealth of INS data (T.Chatterji, ILL) suggesting phase segregation and short range order in manganites, but little theoretical work has been performed up to date. Our group visitor P. Majumdar has started a project with a simple (Holstein double exchange) model. This represents an advance in the methodology but it also enables a direct comparison with experimental data - much of which is obtained at the ILL.

Field induced magnetic order has been observed in spin dimer systems. Experiments at the ILL [B. Grenier et al PRL 2004] have shown interesting new phases of field-induced magnetic order in the compounds Cs3Cr2Br9 and Cs3Cr2Cl9. Theoretical issues, explored in a collaboration of T. Ziman with experimentalists of ILL/CEA, include a description of a Bose-Einstein Condensation of lines of degenerate magnons, which represent the excitations in the ordered phase.

The theory, developed mainly in our group by T. Ziman and G. Bouzerar, provides a framework for understanding recently observed exciting puzzling effects in the spintronics and ferromagnetism of dilute magnetic semiconductors. Spatial inhomogeneity in manganites has been clearly demonstrated by inelastic neutron scattering. Thin films of a material which in the bulk has neither magnetic moments nor magnetic order may become ferromagnetic well above room temperature. [G. Bouzerar and T. Ziman, on the so-called "vacancy induced ferromagnetism", PRL 2006]. This activity is also an illustration of our group approach to numerical methods. The ab-initio computation of exchange integrals (performed by our group visitor J.Kudrnovsky) provides input parameters to a theoretical model which calculates the transition temperatures in Dilute Magnetic Semiconductors [G. Bouzerar et al , EPL 2005]. The problem of calculating the transition temperature is a very ambitious theoretical task, and there are only a few known examples (like BCS superconductors, or Ising model) where the transition temperature can be accurately calculated. This gives an idea of the difficulty of these investigations, which are conducted in our group.

Theoretical description of interacting spins on isolated nano-objects, with applications to giant magnetic molecules [O. Cepas, T. Ziman, Progr. Theor. Phys, 2005], and metal-insulator transitions in manganites [O Cepas et al., PRL 2005] have been carried out. The advantage of this research stands in providing new interesting theoretical ideas on spin dynamics and instantaneous order in a finite size system. No neutron experimental results are however avaiable at ILL yet (however, there are some at Argonne National Labs, USA).