Radio frequency magneto-impedance effect in spin tunneling junctions

The rf magneto-impedance effect of spin tunneling junctions Co/Al-oxide/Co fabricated on glass substrate by ion-beam sputtering is investigated. To measure junction impedance, a measurement method is established. Junction impedance can be determined from the voltages of two cobalt electrodes and a standard resistor at room temperature over a frequency range of 0.1-100 MHz using a lock-in amplifier by taking input impedance into account. The real part of magneto-impedance ratio exhibits a positive value at frequencies less than the roll-off frequency and a negative value at frequencies higher than the roll-off frequency. Furthermore, the imaginary part of the magneto-impedance ratio is found to be positive across the entire frequency region measured and to approach zero at high frequencies. (C) 2004 American Institute of Physics.