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. (C) 2002 American Institute of Physics.