Dresden 2011 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 63: Poster II (Surface Magnetism/ Magnetic Imaging/ Topological Insulators/ Spin Structures and Magnetic Phase Transitions/ Graphene/ Magnetic Thin Films/ Magnetic Semiconductors/ Magnetic Half-metals and Oxides/ Spin-dependent Transport/ Spin Excitations and Spin Torque/ Spin Injection and Spin Currents in Heterostructures/ Spintronics/ Magnetic Storage and Applications)

MA 63.49: Poster

Freitag, 18. März 2011, 11:00–14:00, P2

ZnO thin films with (Li,Ni)-codoping — Senthil Kumar¹, Matthias Althammer², Deepak Venkateshvaran², Eva Karrer-Müller², Sebastian T.B. Goennenwein², M.S. Ramachandra Rao¹, •Matthias Opel², and Rudolf Gross² — ¹Materials Science Research Centre, Indian Institute of Technology Madras, Chennai, India — ²Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany

The wide bandgap II-VI semiconductor ZnO is controversially discussed with regard to both dilute magnetic doping and stable p-type conductivity. Following a recent report [APL 96, 232504 (2010)], we investigated (Li,Ni)-codoping to establish ferromagnetism together with p-type conduction. Using laser-MBE, we deposited thin films from stoichiometric targets with compositions Zn_0.98−xLi_xNi_0.02O (x=0, 0.02, 0.05, 0.09). High-resolution x-ray diffraction reveals excellent structural quality and nearly perfect in-plane orientation. Magnetization measurements show an “S”-shaped behavior in M(H) at room temperature and a clear difference after field cooling or zero-field cooling in M(T) which is reminiscent of superparamagnetism. The saturation magnetic moment is around 0.7 µ_B per Ni and, hence, very close to the bulk value of Ni metal (0.6 µ_B). From thermopower measurements, we obtained negative Seebeck coefficients between −400 µV/K and −900 µV/K, with smaller absolute values corresponding to lower Li concentrations. In summary, we could not confirm p-type conductivity or ferromagnetism in (Li,Ni)-substituted ZnO thin films.

This work was supported by the DAAD and the DFG via SPP 1285.