Voltage driven coexistence of superconductivity and ferromagnetism in ferromagnet/d-wave superconductor/ferromagnet double tunnel junctions

The Blonder-Tinkham-Klapwijk approach is applied to study the sequential tunneling in a ferromagnet (FM)/d-wave superconductor (SC)/FM double tunnel junctions. For antiparallel magnetizations of the two FMs, a ferromagnetic superconducting state with both finite energy gap and finite magnetization appears in the middle SC layer provided that the bias voltage is smaller than a threshold value of the order of the superconducting energy gap. In such a coexistence state, part of the conduction electrons form the Cooper pairs, and the others lead to a finite magnetization.