Magnetoresistance of Fe–SrF2 single-electron devices with a current-in-plane geometry

We fabricated single-electron tunnelling devices with the current-in-plane geometry, which were made of Fe–SrF2 nanogranular films (33. vol%Fe, length: 50–5000 nm, width: 400 nm). Their electric properties such as the current-to-bias voltage curves as well as the tunnelling magnetoresistance (TMR) were investigated by the two terminal measurements. A clear Coulomb blockade (CB) regime was recognized at 8 K when the device length was less than 500 nm. At about the CB threshold voltage, the sign change of TMR ratio was observed while it was +3% (a value corresponding to the data of Fe–SrF2 films in millimeter size) at higher voltage (e.g. 1 V).