Magnetoresistance study in Co–Al–Co and Al–Co–Al double tunneling junctions

Magnetoresistance (MR) in Co–Al–Co and Al–Co–Al double tunneling junctions has been studied at temperatures between 65 and 750 mK and in magnetic fields up to 3 T. The electrical resistance decreases with increasing temperature. In the low magnetic field region, the electrical resistance hysteresis behavior is attributed to a typical TMR for ferromagnetic Co and insulator Al2O3 elements. In the high magnetic field region, a sharp resistance variation roughly near 2.0 T for the Co–Al–Co system and 1.75 T for the Al–Co–Al system has been observed and is attributed to the electron tunneling effect. From the current–voltage and dI/dV characteristics, the superconductivity energy gap is roughly 0.5 meV in the Co–Al–Co system and roughly 0.3 meV in the Al–Co–Al system; and magnetic tunneling energy is roughly 0.01 meV in the Co–Al–Co system and roughly 0.06 meV in the Al–Co–Al system.