Charge and Spin Currents in Ferromagnet-Insulator-Superconductor Tunneling Junctions Using Hg-1223 High-T

Charge and spin currents along the c-axis in ferromagnet-insulator-superconductor (F/I/S) tunneling junctions have been studied within the framework of the tunneling Hamiltonian model. As a superconductor S, HgBa 2 Ca 2 Cu 3 O 8+δ (Hg-1223) with δ = 0.4 copper-oxide high-T c superconductor has been selected, and as a ferromagnet F, Fe metal with bcc structure has been selected for simplicity.The electronic structures of abovematerials have been calculated on the basis of the band theory using the spin-polarized self-consistent-field data for the atomic orbital energies and the universal tight-binding parameters (UTBP) for the interactions. For the η ↑ and η ↓ (= 1 − η ↑ ) defined in the present paper, which are tunneling probabilities of the majority and the minority spin electrons, it is shown that the condition η ↑ = η ↓ means the standard F/I/S tunneling junction with a nonmagnetic insulating layer, and the condition η ↑ ̸ = η ↓ means the F/I/S tunneling junction with a magnetic insulating layer showing a detectable magnetization. We have found that the charge current and the differential conductance nearly remain the same as the change of η ↑ , but the spin current is largely changed due to the change of η ↑ . As an experimental method to detect the change of the spin current, the validity of an X-ray magnetic circular dichroism (XMCD) has been pointed out.