Frequency dependence of magnetoimpedance in spin tunneling junctions

The frequency dependences of the magnetoimpedance for tunneling junctions Al/Al₂O₃/Al and that for coercive differential spin tunneling junctions Co/Al₂O₃/Co fabricated onto glass substrates by ion-beam mask sputtering are investigated and the feasibility of application is discussed. The RF impedance of the tunneling junctions can be understood by the parallel current model of the tunneling and the displacement current. The imaginary part of the impedance of the spin tunneling junction changes in an external magnetic field due to the magnetoresistance effect. The magnetoimpedance ratio is estimated to decrease at high frequencies. Spin tunneling junctions having low resistivity and a low dielectric constant are required in order to obtain high-frequency response. Detection of the imaginary part of the impedance for magnetic sensing may be desirable, because the imaginary part of the magnetoimpedance effect is estimated to be larger than the real part.