In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The computer code system PENELOPE (version 2008) performs Monte Carlo simulation of coupled
electron-photon transport in arbitrary materials for a wide energy range, from a few hundred eV to
about 1 GeV. Photon transport is simulated by means of the standard, detailed simulation scheme.
Electron and positron histories are generated on the basis of a mixed procedure, which combines
detailed simulation of hard events with condensed simulation of soft interactions. A geometry package
called PENGEOM permits the generation of random electron-photon showers in material systems
consisting of homogeneous bodies limited by quadric surfaces, i.e., planes, spheres, cylinders, etc. This
report is intended not only to serve as a manual of the PENELOPE code system, but also to provide the
user with the necessary information to understand the details of the Monte Carlo algorithm.

/pdf/penelope-2006-a-code-system-for-monte-carlo-simulation-of-43nx3zmw6c.pdf

PENELOPE-2006: A Code System for Monte Carlo Simulation of Electron and Photon Transport

Hartree-Fock Compton profiles for the elements

This review is concerned with the utilization of the positron-electron annihilation phenomenon in studies of the physics of condensed matter. The theory of the annihilation process is outlined, the importance of the two-photon mode of decay is established, and it is described how the observable results depend on the initial positron and electron states of the system. A brief account of the principal experimental techniques is included. Discussion of the complex nature of positron behavior in molecular substances suggests the particular value of investigations directed at the two photon pick-off mode of decay of the orthopositronium atoms that are formed in these materials. The possibility of positronium formation in ionic and metallic materials is also considered. The many important electron aspects of positron annihilation in metals are dealt with. The independent particle approach to the analysis of two photon angular distributions is discussed and illustrated. A survey of electronic structure investigations includes studies of polycrystalline and single crystal specimens. The relevance of angular correlation measurements in investigations of the Fermi surfaces of metals and alloys is discussed. More recently developed applications to the study of defected and disordered systems are dealt with. A preliminary account of the interpretation of multicomponentmore » lifetime spectra in terms of varying numbers of distinguishable positron states provides the basis for a discussion of studies of positron trapping by defects, voids. and surfaces in ionic and metallic solids, liquids and powders. (auth)« less

Positron studies of condensed matter

X-ray attenuation coefficients of elements and mixtures

When radiation is Compton-scattered the emerging beam is Doppler broadened because of the motion of the target electrons. An analysis of this broadened lineshape the Crompton profile, provides detailed information about the electron momentum distribution in the scatter. The technique is particularly sensitive to the behaviour of the slower moving outer electrons involved in bonding in condensed matter and can be used to test their quantum-mechanical description. The review begins with a brief survey of the historical development of the subject to within a decade of the present. The behaviour of quantum systems from a momentum viewpoint, is explained and the conditions under which the scattering experiment can be interpreted directly in terms of electron momentum density are discussed. The experimental techniques with gamma -rays, X-rays and electron beams are compared. Finally, recent results on insulators and conductors are surveyed and the extent to which they challenge conventional assumptions of band theory is critically reviewed.

https://iopscience.iop.org/article/10.1088/0034-4885/48/4/001/pdf

Compton scattering and electron momentum determination

A Monte Carlo technique is used to calculate the total intensity and spectral distribution of multiple scattered photons in a typical γ-ray Compton scattering experiment. The method can be used to correct experimental Compton profiles for the effect of multiple scattering. The procedure is applied to two profiles of water measured on samples of different thicknesses and the resultant corrected profiles are seen to be independent of the original sample thickness; furthermore their agreement with a recent calculation using a near Hartree-Fock wave function is significantly improved.

Effect of multiple scattering on experimental Compton profiles: a Monte Carlo calculation

The recent development of the technique of inelastic x-ray scattering to study the electron momentum distribution in the scatterer is surveyed. The simple relationship between the electron momenta and the Compton line shape in the impulse approximation is derived, and the validity of that approximation is discussed in the light of recent measurements. Current areas of research are reviewed.

Compton scattering and electron momentum distributions

The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.

Malcolm Cooper

Papers

Compton scattering and electron momentum determination

Effect of multiple scattering on experimental Compton profiles: a Monte Carlo calculation

Compton scattering and electron momentum distributions

The XMaS beamline at ESRF: instrumental developments and high-resolution diffraction studies.

Spin-dependent momentum distribution in iron studied with circularly polarized synchrotron radiation.