Showing papers by "Saburo Takahashi published in 2001"
TL;DR: In this article, the Coulomb blockade with a clear threshold voltage (Vth) was observed at 4.2 K and the tunnel magnetoresistance (TMR) was enhanced by fabricating nanobridges.
Abstract: We have fabricated granular nanobridge structures consisting of electrodes separated by a nanometer-sized gap in which a thin insulating CoAlO granular film is filled, and measured the current–bias voltage characteristics in a magnetic field to investigate the spin-dependent transport. The Coulomb blockade with a clear threshold voltage (Vth) is observed at 4.2 K. Tunnel magnetoresistance (TMR) is enhanced by fabricating nanobridges. TMR shows a maximum exceeding about 30% at the voltage slightly above Vth. This enhancement is explained by the orthodox theory of single electron tunneling in ferromagnetic multiple tunnel junctions.
78 citations
TL;DR: The Andreev reflection of the ferromagnetic contact is more suppressed than that of the superconducting contact as mentioned in this paper, and the conductance-voltage curve has a bump at zero bias voltage if there is no interfacial scattering.
Abstract: The conductance quantization and Andreev reflection of narrow ferromagnet/superconductor point contacts are theoretically studied. We show that the conductance quantization and the Andreev reflection depend on whether the contact region is superconducting or ferromagnetic as well as on the strength of the exchange field in the ferromagnet. The Andreev reflection of the ferromagnetic contact is more suppressed than that of the superconducting contact. We also show that the conductance-voltage curve has a bump at zero bias voltage if there is no interfacial scattering. On the contrary, the conductance-voltage curve shows a dip if the system has an interfacial scattering.
20 citations
TL;DR: In this paper, the electron transport through a magnetic point contact was studied with special attention to the effect of an atomic scale domain wall, where the magnetization of left and light electrodes are antiparallel.
Abstract: The electron transport through a magnetic point contact is studied with special attention to the effect of an atomic scale domain wall. When the magnetizations of left and light electrodes are antiparallel, the atomic scale domain wall is created inside the contact. We show that the spin precession of conduction electron is forbidden in such an atomic scale domain wall and the sequence of quantized conductances differs from that of the single domain point contact. We also show that the magnetoresistance is strongly enhanced for the narrow point contact and oscillates with the conductance.
7 citations
TL;DR: In this article, the spin-polarized current flowing through a Josephson junction (JJ) in a spin injection device was theoretically studied, and it was shown that not only the Josephson current but also the spin current flow across JJ at zero bias voltage, thereby generating Joule heating by the spin currents.
Abstract: We theoretically study the spin-polarized current flowing through a Josephson junction (JJ) in a spin injection device. When the spin-polarized current is injected from a ferromagnet in a superconductor (SC), the charge current is carried by the superconducting condensate (Cooper pairs), while the spin-up and spin-down currents flow in equal magnitude but in the opposite direction in a SC, because of no quasiparticle charge current in the SC. This indicates that not only the Josephson current but also the spin current flow across JJ at zero bias voltage, thereby generating Joule heating by the spin current. The result provides a new method for detecting the spin current by measuring Joule heating at JJ.
7 citations
TL;DR: In this paper, the spin polarization induced by spin-polarized tunneling competes with the superconductivity in ferromagnetic manganite/high-T c superconductor tunnel junctions.
Abstract: We present non-equilibrium phenomena in ferromagnet/superconductor/ferromagnet tunnel junctions. In the junctions, spin polarization induced by the spin-polarized tunneling competes with the superconductivity. As a result, a variety of non-linear superconducting and magnetoresistive phenomena are expected. The superconducting critical current observed experimentally in ferromagnetic manganite/high- T c superconductor tunnel junctions is analyzed. We also discuss the spin current backflow accompanied by the Josephson current caused by the spin injection.
3 citations