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

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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, HgBa2Ca2Cu3O8+δ (Hg-1223) with δ=0.4 copper-oxide high-Tc superconductor 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 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.