Albert W. Overhauser

Bio: Albert W. Overhauser is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Insensitive nuclei enhanced by polarization transfer & Hyperfine structure. The author has an hindex of 5, co-authored 5 publications receiving 1508 citations.

Polarization of Nuclei in Metals

Abstract: A new method for polarizing nuclei, applicable only to metals, is proposed. It is shown that if the electron spin resonance of the conduction electrons is saturated, the nuclei will be polarized to the same degree they would be if their gyromagnetic ratio were that of the electron spin. This action results from the paramagnetic relaxation processes that occur by means of the hyperfine structure interaction between electron and nuclear spins. A shift of the electron spin resonance due to the same interaction will occur for large amounts of polarization and should provide a direct indication of the degree of polarization.

Isothermal Annealing Effects in Irradiated Copper

Abstract: Copper wires were bombarded with 12-Mev deuterons at low temperatures. The wires were then allowed to anneal isothermally at successive temperatures from -185\ifmmode^\circ\else\textdegree\fi{}C to +167\ifmmode^\circ\else\textdegree\fi{}C. Recovery of the electrical resistivity increase, produced by the bombardment, was observed at all temperatures. The annealing curves obtained for temperatures between -185\ifmmode^\circ\else\textdegree\fi{}C and -60\ifmmode^\circ\else\textdegree\fi{}C were of such a character that only a number of processes with different activation energies could account for them. One-half of the resistivity increase recovered in this range. The activation energies obtained were observed to be proportional to the absolute temperature. A value of 0.44 ev was found near -100\ifmmode^\circ\else\textdegree\fi{}C. Above -60\ifmmode^\circ\else\textdegree\fi{}C the annealing behaved as though it were a single process with a unique activation energy. This process accounted for 25 percent of the increased resistivity and had an energy of 0.68 ev. At room temperature 25 percent of the increase remained, and further anneals to temperatures as high as 167\ifmmode^\circ\else\textdegree\fi{}C produced only an additional 4 percent recovery.Detailed analysis of the data suggests that the single process occurring above -60\ifmmode^\circ\else\textdegree\fi{}C is the result of the annihilation of interstitial atoms and vacancies that are produced by the irradiation. Slight deviations of the recovery rate from that expected of such a second-order process were observed and could be explained as the effect of elastic strains introduced into the lattice by interstitial atoms. The effect of such lattice strains on the rate of vacancy migration was calculated and found to have sufficient magnitude to explain the data. The results also suggested that the low temperature recovery is due to the correlated annihilation of very close interstitial vacancy pairs, the low activation energies being due to large elastic strains in the immediate vicinity of an interstitial. A further result, which can be derived from the activation energy for self-diffusion in copper, is that the energy of formation of a vacancy is 1.39 ev.

Spintronics: Fundamentals and applications

Abstract: 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.

Challenges for semiconductor spintronics

Abstract: High-volume information-processing and communications devices are at present based on semiconductor devices, whereas information-storage devices rely on multilayers of magnetic metals and insulators. Switching within information-processing devices is performed by the controlled motion of small pools of charge, whereas in the magnetic storage devices information storage and retrieval is performed by reorienting magnetic domains (although charge motion is often used for the final stage of readout). Semiconductor spintronics offers a possible direction towards the development of hybrid devices that could perform all three of these operations, logic, communications and storage, within the same materials technology. By taking advantage of spin coherence it also may sidestep some limitations on information manipulation previously thought to be fundamental. This article focuses on advances towards these goals in the past decade, during which experimental progress has been extraordinary.

Magnetic sensors and their applications

Abstract: Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented

Nonlocal magnetization dynamics in ferromagnetic heterostructures

Abstract: Two complementary effects modify the GHz magnetization dynamics of nanoscale heterostructures of ferromagnetic and normal materials relative to those of the isolated magnetic constituents. On the one hand, a time-dependent ferromagnetic magnetization pumps a spin angular-momentum flow into adjacent materials and, on the other hand, spin angular momentum is transferred between ferromagnets by an applied bias, causing mutual torques on the magnetizations. These phenomena are manifestly nonlocal: they are governed by the entire spin-coherent region that is limited in size by spin-flip relaxation processes. This review presents recent progress in understanding the magnetization dynamics in ferromagnetic heterostructures from first principles, focusing on the role of spin pumping in layered structures. The main body of the theory is semiclassical and based on a mean-field Stoner or spin-density-functional picture, but quantum-size effects and the role of electron-electron correlations are also discussed. A growing number of experiments support the theoretical predictions. The formalism should be useful for understanding the physics and for engineering the characteristics of small devices such as magnetic random-access memory elements.