Magnetic impurities in oxides. A novel kind of magnetism?”.

L. A. ERRICO

San Pablo, Brasil

Conferencia; Conferencia invitada dictada en el Departamento de Física, Universidad de San Pablo (USP), Brasil; 2005

Departamento de Física, Universidad de San Pablo, Brasil

Esta conferencia, dictada por invitación en el Instituto de Materiales, USP, Brasil, fue incluida aqui ya que no existe campo para informar conferencias dictadas.  Dilute magnetic impurities in semiconductors (DMS) produce novel materials that may be ferromagnetic at room temperature (RT) and are therefore appealing for spintronics. This is a rapidly developing research area because the electron spin may play a second role role, in addition to the usual charge degree of freedom. Magnetic dopants in nonmagnetic solids are assumed to couple with the electronic states of the host, but remaining magnetically active. For their practical applications, ferromagnetic semiconductors are required to have a high Curie temperature (TC). DMS’s based on II-VI compound semiconductors such as Mn-doped CdTe and ZnSe were the first to be studied. This family of DMS’s has a TC of about 1K and are therefore not useful for practical applications. DMS’s based on III-V semiconductor compounds such as Mn-doped GaAs have TC as high as 110 K but this is still far from room temperature.  Research efforts have continued in order to get higher TC´s and in the last few years RT ferromagnetism has been observed in other Mn-doped compounds such as CdGeP2, ZnGeP2, and ZnO. Recently, Co-doped anatase and rutile TiO2 thin films were reported to be ferromagnetic even above 400 K . These results have motivated intensive studies on the structural and electronic properties of these materials. However, the experimental results strongly depends on the sample preparation and the microscopic mechanism of long-range magnetic order is still an open  problem. Carrier-induced interaction between the magnetic atoms was first suggested as the reason for  ferromagnetism in III-V based DMS. Subsequent reports raised concerns about this idea, due to the possibility of ferromagnetic metal clustering under different growth conditions. Furthermore, it has been suggested that the strong interaction between Co and oxygen vacancies in Co-doped TiO2 plays a key role for the explanation of its high TC. In this talk I will present the structural and magnetic characterization of a set of pulsed laser deposited thin films with nominal composition Ti0.9R0.1O2-d (R = Mn, Fe, Co, Ni, Cu). The crystallographic structures and their magnetic properties were determined. The experimental results are compared to ab initio calculations. Our results support the hypothesis that oxygen vacancies play a key role in the origin of magnetism in doped TiO2 films, and can explain the diversity of experimental results observed experimentally in films grown under different conditions.  This work was partially supported by Conicet, Fund. Antorchas, and ANPCyT (PICT98 03-03727), Argentina,  and TWAS, Italy. L. A. Errico is member of CONICET.  This wor  This wor  This wor  This wor  This wor