Composite Excitation of Josephson Phase and Spin Waves in Josephson Junctions with Ferromagnetic Insulator

Abstract

Coupling of Josephson-phase and spin-waves is theoretically studied in a superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction. Electromagnetic (EM) field inside the junction and the Josephson current coupled with spin-waves in FI are calculated by combining Maxwell and Landau–Lifshitz–Gilbert equations. In the S/FI/S junction, it is found that the current–voltage ( I – V ) characteristic shows two resonant peaks for each mode of the EM field. Voltages at the resonant peaks are obtained as a function of the normal modes of EM field, which indicates a composite excitation of the EM field and spin-waves in the S/FI/S junction. We also examine another type of junction, in which a nonmagnetic insulator (I) is located at one of interfaces between S and FI. In such a S/I/FI/S junction, three resonant peaks appear in the I – V curve, since the Josephson-phase couples to the EM field in the I layer.