Nanoscaled ferromagnetic single-electron transistors

We report on a summary of fabricating and characterizing nanoscaled ferromagnetic single-electron transistors (F-SETs). One type of device is assembled with an atomic force microscope. A single 30 nm Au disc, forming the central island of the transistor, is manipulated with Angstrom precision into the gap between plasma oxidized Ni source and drain electrodes which are designed with different geometries to facilitate magnetic moment reversal at different magnetic fields. The tunnel resistances can be tuned in real-time during the device fabrication by re-positioning the Au disc. A second type of device with Co electrodes and a central Au island is fabricated using a high-precision alignment procedure invoked during e-beam writing. Both devices exhibit single-electron transistor characteristics at 4.2 K. From magnetotransport measurements carried out at 1.7 K, we found that it is more efficient to realize spin injection and detection in Co/Au/Co devices fabricated with the second technique. A maximum TMR of about 4% was observed in these devices.