This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.

http://science.sciencemag.org/content/sci/294/5546/1488.full.pdf

Spintronics: a spin-based electronics vision for the future.

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

/pdf/spintronics-fundamentals-and-applications-2dx38n6phu.pdf

Spintronics: Fundamentals and applications

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Electronic analog of the electro‐optic modulator

Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

/pdf/prospects-of-colloidal-nanocrystals-for-electronic-and-3dxpyhl3r7.pdf

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Tunneling between ferromagnetic films

Ferromagnetic-insulator-ferromagnetic tunneling has been measured in CoFe $/$A${\mathrm{l}}_{2}$${\mathrm{O}}_{3}$ $/$Co or NiFe junctions. At 295, 77, and 4.2 K the fractional change in junction resistance with magnetic field, $\ensuremath{\Delta}R/R$, is 11.8%, 20%, and 24%, respectively. The value at 4.2 K is consistent with Julliere's model based on the spin polarization of the conduction electrons of the magnetic films. $\ensuremath{\Delta}R/R$ changes little with a small voltage bias, whereas it decreases significantly at higher bias $(g0.1\mathrm{V})$, in qualitative agreement with Slonczewski's model. These junctions have potential use as low-power field sensors and memory elements.

Large magnetoresistance at room temperature in ferromagnetic thin film tunnel junctions.

The spin polarization of electrons tunneling from films of Fe, Co, Ni, and Gd to superconducting Al films is determined from conductance measurements. The phenomenological theory of superconducting-normal-metal tunneling is modified to describe superconducting-ferro-magnetic tunneling in a magnetic field. The experimental technique and the method of analysis of the conductance curves to obtain the electron polarization are both described. The observed polarization is positive (majority spin direction predominating) for all the metals; the values obtained were Fe, +44%; Co, +34%; Ni, +11%; and Gd, +4.3%.

SPIN POLARIZATION OF ELECTRONS TUNNELING FROM FILMS OF Fe, Co, Ni, AND Gd.

Tunneling measurements on junctions between very thin superconducting aluminum films and ferromagnetic nickel films in a high magnetic field show that the tunneling current is spin dependent. The effective tunneling density of states in Ni determined by this means implies a polarization of the magnetic moments of the Ni current carriers parallel to the applied field. The technique offers a new method for investigating spin-dependent states in magnetic materials.

Spin-Dependent Tunneling into Ferromagnetic Nickel

An electron-spin polarization $P$ of as much as 80% has been observed in the tunnel current in Au/EuS/Al tunnel junctions. $P$ can be explained by the different heights of the tunnel barriers for the two spin directions. The Zeeman splitting of the Al quasiparticle density of states is greatly enhanced by the exchange interaction at the EuS/Al interface. Spin polarization was even seen in zero applied field. The value of $P$ calculated from the tunneling theory using known barrier heights in EuS is consistent with the measured values.

Electron-spin polarization in tunnel junctions in zero applied field with ferromagnetic EuS barriers.

We have observed electron-spin polarization in the tunnel current in metal-EuS-metal junctions. The value of polarization can be as high as 85%. This polarization is attributed to the exchange splitting of the EuS conduction band as a result of the ferromagnetic transition occurring in EuS at about 15 K. This conduction-band splitting lowers the tunnel barrier height for spin-up electrons and raises it for spin-down electrons, giving rise to spin polarization in the tunnel current. Tunnel barrier lowering is also manifested in the observed decrease of junction resistance with temperature below 15 K. The exchange interaction between quasiparticles in Al and the magnetic ${\mathrm{Eu}}^{2+}$ ions in EuS greatly enhances the Zeeman splitting of the superconducting quasiparticle density of states; in fact, some junctions show Zeeman splitting corresponding to an internal field of ${\mathit{B}}_{\mathit{i}}^{\mathrm{*}}$=3 T before any external magnetic field is applied.

R. Meservey

Papers

Large magnetoresistance at room temperature in ferromagnetic thin film tunnel junctions.

SPIN POLARIZATION OF ELECTRONS TUNNELING FROM FILMS OF Fe, Co, Ni, AND Gd.

Spin-Dependent Tunneling into Ferromagnetic Nickel

Electron-spin polarization in tunnel junctions in zero applied field with ferromagnetic EuS barriers.

Spin-filter effect of ferromagnetic europium sulfide tunnel barriers.