Fabrication of planar-type Ni/vacuum/Ni tunnel junctions based on ferromagnetic nanogaps using field-emission-induced electromigration

摘要

Planar-type Ni/vacuum/Ni tunnel junctions based on ferromagnetic nanogaps were fabricated by field-emission-induced electromigration in an approach that we call "activation." In the activation method, we were simply and easily able to control the tunnel resistance of the nanogaps from 1.6 MΩ to 169 kΩ by adjusting only the magnitude of the field emission current. The resistance of the junction formed by the activation was varied by applying external magnetic fields, and the magnetoresistance (MR) ratio was approximately 12.2% at 16 K with a bias voltage of 0.72 mV. Furthermore, after the bias voltage was increased from 0.72 to 7.3 mV, the MR ratio decreased from 12.2% to 6.2%. When the applied bias voltage was fixed at 1.6 mV, the MR ratio was decreased from 11.6% to 1.2% by increasing the measurement temperature from 16 to 270 K. These results imply that it is possible to easily fabricate planar-type Ni/vacuum/Ni ferromagnetic tunnel junctions via activation.