Showing papers by "Saburo Takahashi published in 2003"
TL;DR: In this paper, the spin transport in a nonmagnetic metal connected to ferromagnetic injector and detector electrodes was studied and a general expression for the spin accumulation signal which covers from the metallic to the tunneling regime was derived.
Abstract: We study theoretically the spin transport in a nonmagnetic metal connected to ferromagnetic injector and detector electrodes. We derive a general expression for the spin accumulation signal which covers from the metallic to the tunneling regime. This enables us to discuss recent controversy on spin injection and detection experiments. Extending the result to a superconducting device, we find that the spin accumulation signal is strongly enhanced by opening of the superconducting gap since a gapped superconductor is a low carrier system for spin transport but not for charge. The enhancement is also expected in semiconductor devices.
444 citations
TL;DR: In this article, a theory of Andreev reflection in a double junction system is presented, where the injected spin polarized quasiparticles convert into Cooper pairs in the superconductor within the range of the penetration depth from the interface.
Abstract: We present a theory of Andreev reflection in a ferromagnet/superconductor/ferromagnet double junction system. In the Andreev reflection process, the injected spin polarized quasiparticles convert into Cooper pairs in the superconductor within the range of the penetration depth from the interface. When the thickness of the superconductor is smaller than or comparable to the penetration depth, the spin polarized quasiparticles pass through the superconductor and therefore the electric current depends on the relative orientation of magnetizations of the ferromagnets. The dependences of the magnetoresistance on the thickness of the superconductor, temperature, the exchange field of the ferromagnets, and the height of the interfacial barriers are analyzed. Our theory explains recent experimental results well.
50 citations
Patent•
24 Jun 2003
TL;DR: In this paper, the authors proposed a spin injection device that includes a first junction 2 having a tunnel junction using a nonmagnetic conductor 4 as a common electrode and another electrode as a ferromagnetic element 6, and a second junction 3 using the non-magnetic conductors 4 as the common conductors and another one as an absorbing element 7.
Abstract: PROBLEM TO BE SOLVED: To provide a spin injection device in which a spin injection magnetic inversion can be performed by raising a spin injection efficiency, and to provide a magnetic device using the same. SOLUTION: The spin injection device includes a first junction 2 having a tunnel junction using a non-magnetic conductor 4 as a common electrode and another electrode as a ferromagnetic element 6, and a second junction 3 using the non-magnetic conductor 4 as the common electrode and another electrode as a ferromagnetic element 7 so that the first junction 2 and the second junction 3 are disposed at a shorter interval than a spin diffusion length of the non-magnetic conductor 4. The first junction 2 is a tunnel junction for spin injection from the ferromagnetic element 6 to the non-magnetic conductor 4, and the ferromagnetic element 7 of the second junction 3 is the absorber of an injected spin current. Thus, a large signal voltage is obtained by low current. When the spin injection device is used as the magnetic device, a high sensitivity magnetic field sensor, a high sensitivity magnetic head, an MRAM (magnetic random access memory) having a large signal voltage, etc., can be provided. COPYRIGHT: (C)2005,JPO&NCIPI
45 citations
TL;DR: In this article, a theory of crossed Andreev reflection in structures consisting of a superconductor with two ferromagnetic leads is presented, and the dependence of the electric current and magnetoresistance on the distance between two magnetoric leads is understood by considering the interference between the wave functions in ferromagnets.
Abstract: A theory of crossed Andreev reflection in structures consisting of a superconductor with two ferromagnetic leads is presented. The electric current due to the crossed Andreev reflection strongly depends on the relative orientation of the magnetization of two ferromagnetic leads. It is shown that the dependence of the electric current and magnetoresistance on the distance between two ferromagnetic leads is understood by considering the interference between the wave functions in ferromagnets. The current and magnetoresistance are calculated as functions of the exchange field and height of the interfacial barriers.
35 citations
TL;DR: In this article, the authors re-examine the spin-glass phase transition of the ±J Heisenberg models with and without random anisotropy D in three dimensions (d = 3) using two complementary methods, i.e., defect energy method and Monte Carlo method.
Abstract: We re-examine the spin-glass (SG) phase transition of the ±J Heisenberg models with and without random anisotropy D in three dimensions (d = 3) using two complementary methods, i.e., (i) the defect energy method and (ii) the Monte Carlo method. We reveal that the conventional defect energy method is not convincing and propose a new method which considers the stiffness of the lattice itself. Using the method, we show that the stiffness exponent θ has a positive value (θ > 0) even when D = 0. Considering the stiffness at finite temperatures, we obtain the SG phase transition temperature of TSG ~ 0.19J for D = 0. On the other hand, a large scale MC simulation shows that, in contrast to the previous results, a scaling plot of the SG susceptibility χSG for D = 0 is obtained using almost the same transition temperature of TSG ~ 0.18J. Hence we believe that the SG phase transition occurs in the Heisenberg SG model in d = 3.
19 citations
TL;DR: In this paper, the effects of high pressure on tunnel transport and magnetoresistance have been investigated in insulating granular films and it is found that the temperature dependence of electrical resistivity is affected strongly by applying pressure.
Abstract: Effects of high pressure on tunnel transport and magnetoresistance have been investigated in ${\mathrm{Co}}_{52}{\mathrm{Al}}_{20}{\mathrm{O}}_{28}$ insulating granular films It is found that the temperature dependence of electrical resistivity $\ensuremath{\rho}(T)$ is affected strongly by applying pressure while the ${T}^{\ensuremath{-}1/2}$ dependence in $\ensuremath{\rho}(T)$ is still observed at high pressures Furthermore, tunnel magnetoresistance is enhanced by more than 2% at 31 GPa The results are discussed briefly on the basis of higher-order tunneling theory
6 citations
TL;DR: In this paper, the anomalous Hall effect induced by a spin-polarized current in superconductors was theoretically studied and it was shown that the Hall voltages due to side jump and skew scattering have different temperature dependence in the superconducting state.
Abstract: Anomalous Hall effect induced by a spin-polarized current in superconductors (SC) is theoretically studied. The spin-polarized quasiparticles flowing in SC are deflected by spin-orbit impurity scattering to create the charge accumulation in the transverse direction. Due to overall charge neutrality, a compensating change appears in the pair density of the condensate. To maintain the electrochemical potential of the condensate spatially constant, an electric field builds up in the transverse direction, yielding the Hall voltage. It is shown that the Hall voltages due to side jump and skew scattering have different temperature dependence in the superconducting state.
2 citations
TL;DR: In this paper, it was shown that the transition between consecutive charge states can occur via high-spin states, which significantly modifies the shape of Coulomb steps and gives rise to additional resonances at low temperatures.
Abstract: It is shown that nonequilibrium spin fluctuations significantly influence electronic transport in a single-electron transistor, when the spin relaxation on the island is slow. To describe spin fluctuations, the “orthodox” tunneling theory is generalized by taking into account the electron spin. It is shown that the transition between consecutive charge states can occur via high-spin states, which significantly modifies the shape of Coulomb steps and gives rise to additional resonances at low temperatures.
1 citations
TL;DR: In this article, the effect of Andreev reflection in ferromagnetic/superconductor/ferromagnet structures was studied theoretically and it was shown that the spin-polarized quasiparticle current penetrates to the superconductor in the range of penetration depth from the interfaces, and thus the current depends on the relative orientation of magnetization of the ferromagnets.
Abstract: We study theoretically the effect of Andreev reflection in ferromagnet/superconductor/ferromagnet structures. The spin-polarized quasiparticle current penetrates to the superconductor in the range of penetration depth from the interfaces, and thus the current depends on the relative orientation of magnetization of the ferromagnets. We show that the current is controlled by the Andreev reflection at the interfaces.