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.

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Spintronics: Fundamentals and applications

This paper describes the use of novel two-dimensional nuclear magnetic resonance (NMR) pulse sequences to provide insight into protein dynamics. The sequences developed permit the measurement of the relaxation properties of individual nuclei in macromolecules, thereby providing a powerful experimental approach to the study of local protein mobility. For isotopically labeled macromolecules, the sequences enable measurements of heteronuclear nuclear Overhauser effects (NOE) and spin-lattice (T1) and spin-spin (T2) 15N or 13C relaxation times with a sensitivity similar to those of many homonuclear 1H experiments. Because T1 values and heteronuclear NOEs are sensitive to high-frequency motions (10(8)-10(12) s-1) while T2 values are also a function of much slower processes, it is possible to explore dynamic events occurring over a large time scale. We have applied these techniques to investigate the backbone dynamics of the protein staphylococcal nuclease (S. Nase) complexed with thymidine 3',5'-bisphosphate (pdTp) and Ca2+ and labeled uniformly with 15N. T1, T2, and NOE values were obtained for over 100 assigned backbone amide nitrogens in the protein. Values of the order parameter (S), characterizing the extent of rapid 1H-15N bond motions, have been determined. These results suggest that there is no correlation between these rapid small amplitude motions and secondary structure for S. Nase. In contrast, 15N line widths suggest a possible correlation between secondary structure and motions on the millisecond time scale. In particular, the loop region between residues 42 and 56 appears to be considerably more flexible on this slow time scale than the rest of the protein.

Backbone dynamics of proteins as studied by 15N inverse detected heteronuclear NMR spectroscopy: application to staphylococcal nuclease.

One of the most exciting developments in the areas of catalysis, organometallic chemistry, and polymer science in recent years has been the intense exploration and commercialization of new polymerization technologies based on single-site and metallocene coordination olefin polymerization catalysts.1 The vast number of specifically designed/synthesized transition metal complexes (catalyst precursors) and main-group organometallic compounds (cocatalysts) allows unprecedented control over polymer microstructure, the generation of new polymer architectures, and the development of new polymerization reactions. Commercialization of new generations of single-site and metallocene catalyst-based technologies has provided the multibillion pound per year polyolefins industry with the ability to deliver a wide range of new and innovative olefin-based polymers having improved properties.2-4 The intense industrial activity in the field and the challenges to our basic understanding that have come to light have in turn 1391 Chem. Rev. 2000, 100, 1391−1434

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Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure−Activity Relationships

Exchange anisotropy — a review

Nuclear magnetic resonance methods for quantifying microsecond-to-millisecond motions in biological macromolecules.

NMR of Chemically Exchanging Systems

A general theory of the nonsaturated NMR spectra of chemically exchanging molecules is formulated. As an example the case of a molecule with two nonequivalent protons exchanging with a molecule with one proton is worked out in detail. Connection is made with previous theories by taking limiting expressions of the general results. In the appendix it is shown how the method can be extended to include saturation and hindered rotation.

Exchange Broadening in Nuclear Magnetic Resonance

Generalized Bloch‐Type Equations for Chemical Exchange

Application of the Diffusion-Modified Bloch Equation to Electron Spin Resonance in Ordinary and Ferromagnetic Metals

The magnetic dipole energies of MnO and of the normal and inverse spinel structures are calculated. It is found that with this interaction alone MnO would have its direction of spin alignment in a (111) plane, in contrast to the experimentally found [100]. The addition of a nearest neighbor quadrupole interaction is suggested as a means of making the [100] direction preferred. The normal and the inverse spinel structures are found to have zero magnetic dipole energies.

Jerome I. Kaplan

Papers

NMR of Chemically Exchanging Systems

Exchange Broadening in Nuclear Magnetic Resonance

Generalized Bloch‐Type Equations for Chemical Exchange

Application of the Diffusion-Modified Bloch Equation to Electron Spin Resonance in Ordinary and Ferromagnetic Metals

Magnetic Dipolar Interactions in MnO and in Ferrites