Parts | Days | Selection | Search | Downloads | Help
TT: Fachverband Tiefe Temperaturen
TT 39: Transport: Nanoelectronics II - Spintronics and Magnetotransport
TT 39.2: Talk
Friday, February 29, 2008, 10:45–11:00, EB 202
Simultaneous ferromagnetic semiconductor-metal transition in Gd-doped EuO — •Michael Arnold and Johann Kroha — Physikalisches Institut, Universität Bonn
At room temperature, europium oxide, EuO, is a paramagnetic semiconductor with a large band gap of 1.2 eV which undergoes a ferromagnetic ordering transition at a Curie temperature of TC=69 K. Upon minute electron doping, this transition turns into a simultaneous ferromagnetic semiconductor-metal transition, with nearly 100 % of the conduction electrons polarized and a huge magnetoresistance effect. This has made EuO a prototypical material for possible spintronics applications.
Here we present a general framework for describing this phase transition in Gd-doped EuO. This system is described by a Heisenberg lattice of the Eu 4f moments S=7/2, a conduction band (which in the high-temperature phase is empty), and singly occupied impurity levels in the gap, provided by the Gd 5d orbitals. The theory correctly describes detailed experimental features of the conductivity and of the magnetization, in particular the enhancement of TC by a minute Gd doping concentration. The existence of correlation-induced local moments on the impurity sites is essential for this description. We also predict that the ferromagnetic semiconductor-metal transition can be switched by applying a gate voltage to EuO films.