Exchange effects on electron transport through single-electron spin-valve transistors

Abstract

We study electron transport through single-electron spin-valve transistors in the presence of nonlocal exchange between the ferromagnetic leads and the central normal-metal island. The Coulomb interaction is described with the "orthodox model" for Coulomb blockade and we allow for noncollinear lead magnetization directions. Two distinct exchange mechanisms that have been discussed in the literature are shown to be of comparable strength and are taken into account on equal footing. We present results for the linear conductance as a function of gate voltage and magnetic configuration, and discuss the response of the system to applied magnetic fields.

Modeling electron-spin accumulation in a metallic nanoparticle

“…In sequential electron tunneling via the nanoparticle, spin-polarized current is a consequence of spin accumulation, a difference in the chemical potentials of the spin-up and spin-down electrons in the nanoparticle, caused by the tunnel electric current and the spin-polarized densities of states. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Spin accumulation is found only in the antiparallel magnetization configuration, because only in that case the ratios of the tunnel-in and tunnel-out resistances of the spin-up and the spin-down electrons are different. A necessary condition for spin accumulation is that the electron spin be conserved during the sequential transport process.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Consequently our explanation of the saturation was qualitative. The goal of this paper is to obtain a model of spin-polarized electron transport through a metallic nanoparticle to explain our observations.…”

“…The tunneling regime in our devices is different from that used in the theoretical studies, because the tunnel resistances in our junctions are highly asymmetric and the spin-relaxation rate has strong energy dependence. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Other experimental work on arrays and single nanoparticles did not find any saturation of the spin-polarized current with bias voltage. 5,[27][28][29][30][31] These experiments do not measure TMR in the regime of well-resolved energy levels; we believe that this is a critical measurement to separate the contributions to TMR from the chemical potential shifts.…”

Saturation of spin-polarized current in nanometer scale aluminum grains

“…[8,9,10,11,12] In addition, there is a major effort to study nanospintronics using carbon-nanotubes; see Ref. [13] and references therein.…”

Current fluctuations in noncollinear single-electron spin-valve transistors

“…Furthermore, the system exhibits an interaction-induced exchange field that exists between the central region and the leads. 45,46,61 This fictitious field is evoked by virtual tunneling processes between the interacting central region and the polarized leads and results in a precession of the accumulated island spin. The existence of such an exchange field in mesoscopic conductors was firstly theoretically described 80 and experimentally confirmed [81][82][83] in the context of quantum dots coupled to ferromagnetic reservoirs.…”