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The unique aspects of neutron scattering in biology rely largely on the extraordinary parameters of interaction of neutrons with hydrogen nuclei. The origin of isotopic and spin incoherent scattering and its possible implication for neutron diffraction from protein crystals are described. The impact of a change in the coherent scattering length of hydrogen nuclei with isotopic substitution and spin polarization is illustrated by a number of applications in structural biology, which show clearly the complementarity to x-ray diffraction. A more detailed account is given of polarized neutron scattering from dynamically polarized spin systems. Experimental evidence for the existence of selectively polarized proton spin domains and their use in structural studies is presented.

This review has two aims: (i) to present the formalism which describes the spin-polarization observables in terms of spin-state transition amplitudes in a manner that reveals the required correspondence between the theoretical and experimental definitions of the observables; then (ii) to emphasize that spin physics, the experimental and theoretical investigations of spin-polarization effects in scattering and reactions, has become a clear unifying element among the otherwise seemingly disparate fields of nuclear, particle and electron-scattering physics. Illustrative examples of research results in these fields are used to demonstrate this commonality. The important role of intrinsic spin in providing experimental investigations of parity conservation, charge symmetry and time-reversal invariance is discussed.

We report on the recently developed technique of magnetic-field-dependent small-angle neutron scattering (SANS), with attention to bulk ferromagnets exhibiting random magnetic anisotropy. In these materials, the various magnetic anisotropy fields (magnetocrystalline, magnetoelastic, and/or magnetostatic in origin) perturb the perfectly parallel spin alignment of the idealized ferromagnetic state. By varying the applied magnetic field, one can control one of the ordering terms which competes with the above-mentioned perturbing fields. Experiments which explore the ensuing reaction of the magnetization will therefore provide information not only on the field-dependent spin structure but, importantly, on the underlying magnetic interaction terms. This strategy, which underlies conventional studies of hysteresis loops in magnetometry, is here combined with magnetic SANS. While magnetometry generally records only a single scalar quantity, the integral magnetization, SANS provides access to a vastly richer data set, the Fourier spectrum of the response of the spin system as a function of the magnitude and orientation of the wave vector. The required data-analysis procedures have recently been established, and experiments on a number of magnetic materials, mostly nanocrystalline or nanocomposite metals, have been reported. Here, we summarize the theory of magnetic-field-dependent SANS along with the underlying description of random anisotropy magnets by micromagnetic theory. We review experiments which have explored the magnetic interaction parameters, the value of the exchange-stiffness constant as well as the Fourier components of the magnetic anisotropy field and of the magnetostatic stray field. A model-independent approach, based on the experimental autocorrelation function of the spin misalignment, provides access to the characteristic length of the spin misalignment. The field dependence of this quantity is in quantitative agreement with the predictions of micromagnetic theory. Experiments on nanocomposite ferromagnets reveal that the jump of the magnetization at internal phase boundaries leads to a significant magnetostatic perturbing field, with an unusual 'clover-leaf' SANS pattern as the experimental signature. Furthermore, SANS experiments have been used to monitor the orientation of magnetic domains as well as the length scale of intradomain spin misalignment.

Spintronics is a rapidly growing field focusing on phenomena and related devices essentially dependent on spin transport. Some of them are already an established part of microelectronics. We review recent theoretical and experimental advances in achieving large spin injection efficiency (polarization of current) and accumulated spin polarization. These include tunnel and giant magnetoresistance, spin-torque and spin–orbit effects on electron transport in various heterostructures. We give a microscopic description of spin tunneling through oxide and modified Schottky barriers between a ferromagnet (FM) and a semiconductor (S). It is shown that in such FM–S junctions electrons with a certain spin projection can be efficiently injected into (or extracted from) S, while electrons with the opposite spin can accumulate in S near the interface. The criterion for efficient injection is opposite to a known Rashba criterion, since the barrier should be rather transparent. In degenerate semiconductors, extraction of spin can proceed at low temperatures. We mention a few novel spin-valve ultrafast devices with small dissipated power: a magnetic sensor, a spin transistor, an amplifier, a frequency multiplier, a square-law detector and a source of polarized radiation. We also discuss effects related to spin–orbital interactions, such as the spin Hall effect (SHE) and a recently predicted positive magnetoresistance accompanying SHE. Some esoteric devices such as 'spinFET', interacting spin logic and spin-based quantum computing are discussed and problems with their realization are highlighted. We demonstrate that the so-called 'ferroelectric tunnel junctions' are unlikely to provide additional functionality because in all realistic situations the ferroelectric barrier would be split into domains by the depolarizing field.

Surveys the experimental studies and related analyses of such processes in p-type ZnTe, GaP, SiC and InSb. The observed scattering mechanisms include free heavy-hole spin flip, spin flip of holes bound to shallow acceptors spin flip of photoexcited electrons, and several exciton processes. A variety of photoexcited transitions which yield spin temperatures up to 300K in systems with lattice temperatures below 2K. Multiple spontaneous spin-flip scattering and spin-flip plus phonon scattering mechanisms are discussed.