Enhanced spin accumulation and novel magnetotransport in nanoparticles

Yakushiji, Kay; Ernult, F.; Imamura, Hiroshi; Yamane, K.; Mitani, Seiji; Takanashi, Kōki; Takahashi, Saburo; Maekawa, Sadamichi; Fujimori, H.

doi:10.1038/nmat1278

Cited by 169 publications

(162 citation statements)

References 29 publications

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“…4a), we can visualize a completely different sequence of oscillations when comparing both Co foil and Co-NPs sample data. The latter being almost identical 20 to that of Co 3 O 4 . 28 The Fourier transforms (FT) of the k 3 -weighted experimental data corresponding to Co foil and CoNPs sample are depicted in Fig.…”

Section: Morphology and Structural Characterizationsupporting

confidence: 62%

“…The fabrication and manipulation of monodispersed metallic 20 and magnetic nanoparticles (NPs) has opened some of the current more promising applications in materials science or biosciences. [1][2][3] Magnetic NPs can be easily manipulated by external magnetic field gradients and thus, be used for separation of different catalytic solids, hyperthermia 25 treatments or magnetic resonance imaging.…”

Section: Introductionmentioning

confidence: 99%

“…3) would completely mask this AFM signal. 20 Other possibility is that the presence of AFM small grains with uncompensated spins and disorder generated by grain boundaries are likely at a very thin (< 1 nm) CoO layer, due to the roughness and intermixing at the interface. 36, 37 Therefore, the maximum seen in the FC and the EB effect could be 25 associated with the transition into a frozen state of the spinglass (SG) Co-oxide shell.…”

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confidence: 99%

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Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Fernández-García

Gorría

Sevilla

et al. 2011

Phys. Chem. Chem. Phys.

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Section: Morphology and Structural Characterizationsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Fernández-García

Gorría

Sevilla

et al. 2011

Phys. Chem. Chem. Phys.

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“…A sf in the microsecond regime has been reported for Co nanoclusters. 6 The long spin-flip times in small clusters is not yet fully understood; it might simply be due to the probability of finding zero impurities in a given small cluster.In this Rapid Communication we discuss aspects of electron transport in metallic SV-SETS with noncollinear magnetization directions. It turns out that an effective exchange effect between the spin accumulation and the magnetizations has to be taken into account.…”

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confidence: 99%

Noncollinear single-electron spin-valve transistors

2005

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We study interaction effects on transport through a small metallic cluster connected to two ferromagnetic leads ͑a single-electron spin-valve transistor͒ in the "orthodox model" for the Coulomb blockade. The nonlocal exchange between the spin accumulation on the island and the ferromagnetic leads is shown to affect the transport properties such as the electric current and spin-transfer torque as a function of the magnetic configuration, gate voltage, and applied magnetic field. DOI: 10.1103/PhysRevB.72.020407 PACS number͑s͒: 85.75.Ϫd, 72.25.Mk, 73.23.Hk Magnetoelectronics is a contender to fulfill the technological need for faster and smaller memory and sensing devices. The drive into the nanometer regime brings about an increasing importance of electron-electron interaction effects. Small metallic clusters ͑islands͒ that are electrically contacted to metallic leads by tunnel junctions and capacitively coupled to a gate electrode can behave as "singleelectron transistors ͑SETs͒." In the Coulomb-blockade regime, the charging energy needed to change the electron number on the island by one exceeds the thermal energy, and transport can be controlled on the level of the elementary charge. 1 In a spin-valve SET ͑SV-SET͒, the contacts to the cluster consist of ferromagnetic metals ͑F͒. We focus here on F͉N͉F structures with normal-metal ͑N͒ islands ͓see Fig. 1͑a͔͒, 2 since these "spin valves" display giant magnetoresistance and spin-current-induced magnetization reversal. 3 Other combinations such as F͉F͉F ͑Ref. 4͒, N͉N͉F ͑Ref. 5͒, or F͉F͉N ͑Refs. 6 and 7͒ are of interest as well.Several theoretical studies have been devoted to the binary magnetoresistance ͑MR͒ of SV-SETs, i.e., the difference in the electric resistance between parallel and antiparallel configurations of the magnetization directions. 8,9 Interaction effects in magnetic devices have been studied as well for spin valves with a Luttinger liquid island 10 and for single-level quantum dots 11-13 with noncollinear magnetic configurations.A necessary condition for a significant MR in F͉N͉F structures is a spin accumulation on the normal-metal island, viz. a sufficiently long spin-flip relaxation time sf . Seneor et al. 14 have measured the MR of SV-SETs with gold islands with a sf ϳ 800 ps. A sf in the microsecond regime has been reported for Co nanoclusters. 6 The long spin-flip times in small clusters is not yet fully understood; it might simply be due to the probability of finding zero impurities in a given small cluster.In this Rapid Communication we discuss aspects of electron transport in metallic SV-SETS with noncollinear magnetization directions. It turns out that an effective exchange effect between the spin accumulation and the magnetizations has to be taken into account.We take the junction resistances sufficiently larger than the quantum resistance R Q = h / e 2 so that the Coulomb blockade can be treated by lowest-order perturbation theory. We furthermore disregard the size quantization of states in the clusters, thus adopting the well-esta...

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“…So far experimental verification of spin accumulation in F-SETs has been elusive. Only very recently two experiments 14,15 have shown indirect evidence of its occurrence, albeit the interpretation of one of them 14 has been controversial 16 .…”

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confidence: 99%

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

et al. 2006

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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.

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Enhanced spin accumulation and novel magnetotransport in nanoparticles

Cited by 169 publications

References 29 publications

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Co nanoparticles inserted into a porous carbon amorphous matrix: the role of cooling field and temperature on the exchange bias effect

Noncollinear single-electron spin-valve transistors

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

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