Probing Spin Accumulation in Ni/Au/Ni Single-Electron Transistors with Efficient Spin Injection and Detection Electrodes

Abstract

We have investigated spin accumulation in Ni/Au/Ni single-electron transistors assembled by atomic force microscopy. The fabrication technique is unique in that unconventional hybrid devices can be realized with unprecedented control, including real-time tunable tunnel resistances. A grid of Au discs, 30 nm in diameter and 30 nm thick, is prepared on a SiO 2 surface by conventional e-beam writing. Subsequently, 30 nm thick ferromagnetic Ni source, drain and sidegate electrodes are formed in similar process steps. The width and length of the source and drain electrodes were different to exhibit different coercive switching fields. Tunnel barriers of NiO are realized by sequential Ar and O 2 plasma treatment. Using an atomic force microscope with specially designed software, a single non-magnetic Au nanodisc is positioned into the 25 nm gap between the source and drain electrodes. The resistance of the device is monitored in real-time while the Au disc is manipulated step-by-step with Ångstrom-level precision. Transport measurements in magnetic field at 1.7 K reveal no clear spin accumulation in the device, which can be attributed to fast spin relaxation in the Au disc. From numerical simulations using the rateequation approach of orthodox Coulomb blockade theory, we can put an upper bound of a few ns on the spin-relaxation time for electrons in the Au disc. To confirm the magnetic switching characteristics and spin injection efficiency of the Ni electrodes, we fabricated a test structure consisting of a Ni/NiO/Ni magnetic tunnel junction with asymmetric dimensions of the electrodes similar to those of the SETs. Magnetoresistance measurements on the test device exhibited clear signs of magnetic reversal and a maximum TMR of 10%, from which we deduced a spinpolarization of about 22% in the Ni electrodes.

Fabrication of vertically aligned carbon nanotubes for spintronic device applications

“…12 In some recent works, the same model was also used to explain the MR in FTJ system. 45,46 According to this model the magnetoresistance is given by…”

Anisotropic magnetoresistance in nanocontacts

“…We study a single electron transistor ͑SET͒ with Ni electrodes 19,37,38 and a nonmagnetic central island ͑CI͒ with a discrete electronic spectrum. The CI is weakly coupled to the electrodes, so that the levels acquire a broadening ⌫.…”

“…In this section we consider a different scenario, motivated by recent experiments 15 and by the remarks at the end of the previous section. We study a single electron transistor (SET) with Ni electrodes 19,37,38 and a nonmagnetic central island (CI) with a discrete electronic spectrum. The CI is weakly coupled to the electrodes, so that the levels acquire a broadening Γ.…”

Fabrication of nanodamascene metallic single electron transistors with atomic layer deposition of tunnel barrier

“…9 This is of great importance since previously, only native oxides of the metal electrodes (e.g., Al, Cr, Ti, and Ni) formed the tunnel barrier in metal-based SETs. [10][11][12][13][14] Moreover, the use of ALD enables formation of low-k SiO 2 dielectric on metal substrates. Figure 1 shows the schematic of the fabrication steps in MIM nanodamascene SETs.…”