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MA: Fachverband Magnetismus

MA 29: Micro- and Nanostructured Magnetic Materials

MA 29.4: Vortrag

Mittwoch, 13. März 2013, 15:45–16:00, H23

Nanopatterning of linear GMR spin valves by FIB milling — •Benjamin Riedmüller, Felix Huber, and Ulrich Herr — Universität Ulm, Institut für Mikro- und Nanomaterialien

In this work we present a detailed investigation of a focused-ion-beam (FIB) nanopatterning process for linear spin valves consisting of Si/SiO₂[300]/Ta[5]/NiFe[6]/Co[1]/Cu[4]/Co[4]/FeMn[20]/Ta[5] (numbers are thickness in nm) to widths down to 150 nm. Our results show that without any further protective layer the spin valves show a drastic decrease in magneto-resistive (MR) properties after the FIB cutting even for widths >1 µm. This is accompanied by a decrease of interlayer exchange coupling (J_ex) at the AFM/FM interface. These results can be explained by a Ga bombardment near the cutting edges with stray irradiation of the ion beam which limits the process and does not allow a successive nanopatterning of the MR devices. The observed decrease in MR functionality can be correlated with a lateral ion irradiation that shows a similar decrease of the GMR-ratio and an increase in spin valve resistance for doses higher than 1·10¹³/cm². For protecting the spin valves from the unwanted ion damage a 50 nm SiO₂ cover layer is deposited by ion beam evaporation on the spin valves. After FIB cutting a smaller decrease of the MR ratio and AFM/FM coupling can be seen which proves the protective function of the SiO₂ layer and therefore allows sensor dimensions < 200 nm. The nanostructuring is accompanied by a drastic change in the magnetic reversal and switching behaviour of the magnetic layers which can be understood as a consequence of the small widths of the sensor elements.