Spin-tuned Conductivity in Antiferromagnetic Semiconductors

During this project I will investigate the structural and magnetotransport properties of semiconductor antiferromagnetic thin films. The ultimate goal is the demonstration of the spin-controlled conductivity of a semiconductor device near room temperature. I will join the groups of Vclav Hol (Charles University in Prague) and and Tomš Jungwirth (Institute of Physics ASCR in Prague) to pursue this goal. So far spintronics applications are mostly based on metallic ferromagnets. For example hard-disk read heads based on the tunneling magnetoresistance effect are using CoFe layers in a spin-valve structure whose electrical resistance depends on the relative orientation of the magnetic moments in the CoFe layers. A fundamentally different approach is to use antiferromagnets as the active component in spintronics devices. Devices based on antiferromagnets offer several advantages since they are not sensitive to weak external fields and do not produce stray fields due to their compensated magnetic moments. Just recently the groups of the project hosts have proven a spin-valve like signal in a tunnel junction based on an metallic antiferromagnet at T=4 K (Nat. Mater. 10 (2011) 347). We would like to extend this concept and investigate the vertical transport in metal/MnTe/ferromagnet stacks with the goal to to find a resistance depending on the applied magnetic field direction near room- temperature. We chose to investigate hexagonal MnTe since it is a II-VI semiconductor formed from Mn- ions with a large magnetic moment and critical temperature of 310 K above room-temperature. The group of Gunther Springholz at the University of Linz/Austria has grown such hexagonal MnTe layers using molecular beam epitaxy and will provide them for the purpose of this project. We will perform detailed analysis of the structural properties using x-ray diffraction and reflectometry to optimize the crystalline and surface properties. In a first step we will investigate the transport properties of bare MnTe layers in dependence of magnetic field and extend our studies towards exchange coupling at the interface of Fe and MnTe and the magnetoresistance in metal/MnTe/Fe devices. In a return phase to the Institute of Semiconductor and Solid State Physics at the University Linz I would like to investigate how the above devices depend on strain induced either via growth on different substrate or in- situ by strain tuning using an piezoelectric actuator driven by electrical voltage.

No additional funding sources recorded.