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

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 csuperconductor has been selected, and as a ferromagnet F , Fe metal with bcc structure has been selected for simplicity. The electronic structures of above materials 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 theη ↑andη ↓ ( = 1 - η ↑ ) defined in the present paper, which are tunneling probabilities of the majority and the minority spin electrons, it is shown that the conditionη ↑ = η ↓means the standard F/I/S tunneling junction with a nonmagnetic insulating layer, and the conditionη ↑ ≠ 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 ofη ↑, but the spin current is largely changed due to the change ofη ↑. 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.