L.M.C. Perreira - Instituut voor Kern- en Stralingsfysica, KU Leuven, Belgium
Lundi 23 septembre 2013 à 11 h - Barre 22-23 - Salle 317 - 3e étage
In a dilute magnetic semiconductor (DMS), magnetic atoms are introduced in an otherwise non-magnetic semiconductor. The discovery of a DMS which is ferromagnetic above room temperature would be a crucial step towards the development of semiconductor spintronics. Despite the success of narrow-gap DMS materials such as Mn-doped GaAs and InAs, where ferromagnetism and semiconducting behavior do co-exist, producing rich spintronic phenomena, the maximum achievable Curie temperatures remain well below room temperature (< 200 K). Although higher Curie temperatures have been predicted and reported for wide-gap DMS materials such as transition-metal doped ZnO and GaN, there is yet no clear consensus that intrinsic ferromagnetism is established in such materials. The fundamental issue is the lack of a demonstrated mechanism of magnetic interaction which is sufficiently strong and long-ranged to produce high-temperature magnetic order in such dilute magnetic compounds. There is however an alternative new picture in which ferromagnetic order can emerge from single-ion phenomena, in the absence of magnetic interaction. Oxides doped with transition-metal impurities occupying sites with octahedral O-coordination (e.g. Ti-substituted Fe-doped SrTiO3, i.e. SrTi1-xFexO3) are good candidate materials to exhibit such behavior.
In this talk, I will give an overview of ongoing experimental studies on the local magneto-structural properties of Fe-doped SrTiO3 (prepared by ion implantation and thermal annealing), based on a combination of in-house techniques, such as SQUID magnetometry, Rutherford backscattering and channeling spectroscopy, atom-probe tomography and conversion electron Mossbauer spectroscopy, as well as large-scale facility methods, such as β- emission channeling (at ISOLDE-CERN, Geneva), X-ray absorption fine structure (at ESRF, Grenoble), synchrotron radiation X-ray diffraction (at ESRF, Grenoble), and polarized neutron reflectivity (at LLB, Saclay). I will discuss the atomic-scale origin of the observed room-temperature ferromagnetism, as well as prospects for controlling and exploiting the phenomenon.