Polarization Analysis Of Neutron Scattering From Magnetic Alloys

Magnetic Small-Angle Neutron Scattering provides the first extensive treatment of magnetic small-angle neutron scattering (SANS). The theoretical background required to compute magnetic SANS cross sections and correlation functions related to long-wavelength magnetization structures is laidout. The concepts are scrutinized based on the discussion of experimental neutron data. Regarding prior background knowledge, some familiarity with the basic magnetic interactions and phenomena as well as scattering theory is desired.Besides exposing the different origins of magnetic SANS, and furnishing the basics of the magnetic SANS technique in early chapters, a large part of the book is devoted to a comprehensive treatment of the continuum theory of micromagnetics, as it is relevant for the study of the elastic magneticSANS cross section. Analytical expressions for the magnetization Fourier components allow to highlight the essential features of magnetic SANS and to analyze experimental data both in reciprocal, as well as in real space. Later chapters provide an overview on the magnetic SANS of nanoparticles andso-called complex systems (e.g., ferrofluids, magnetic steels, spin glasses and amorphous magnets). It is this subfield where major progress is expected to be made in the coming years, mainly via the increased usage of numerical micromagnetic simulations (Chapter 7), which is a very promisingapproach for the understanding of the magnetic SANS from systems exhibiting nanoscale spin inhomogeneity.

This book provides the experimental condensed-matter researcher with a description of the variety of material characteristics which can now be investigated with polarized neutrons. Included are two extensive chapters on basic theory and currently available instrumentation, and a presentation and discussion of scientific results obtained from a wide range of experiments: diffraction, critical reflection, elastic and inelastic polarization analysis, and neutron spin precession methods like spin-echo spectroscopy.

Neutron Scattering from Magnetic Materials is a comprehensive account of the present state of the art in the use of the neutron scattering for the study of magnetic materials. The chapters have been written by well-known researchers who are at the forefront of this field and have contributed directly to the development of the techniques described. Neutron scattering probes magnetic phenomena directly. The generalized magnetic susceptibility, which can be expressed as a function of wave vector and energy, contains all the information there is to know about the statics and dynamics of a magnetic system and this quantity is directly related to the neutron scattering cross section. Polarized neutron scattering techniques raise the sophistication of measurements to even greater levels and gives additional information in many cases. The present book is largely devoted to the application of polarized neutron scattering to the study of magnetic materials. It will be of particular interest to graduate students and researchers who plan to investigate magnetic materials using neutron scattering. · Written by a group of scientist who have contributed directly in developing the techniques described.· A complete treatment of the polarized neutron scattering not available in literature.· Gives practical hits to solve magnetic structure and determine exchange interactions in magnetic solids.· Application of neutron scattering to the study of the novel electronic materials.

Neutron polarization analysis experiments, and unpolarized neutron scattering experiments, were made on annealed single crystal Cu-Mn samples of 5, 10, 15, and 25 at. % Mn. Peaks in the magnetic diffuse scattering are found at the (1, 1/2 +- delta, 0)-type positions in reciprocal space, where delta = 0.34, 0.29, 0.25 and 0.19 for the 5, 10, 15 and 25% Mn samples respectively. This magnetic scattering is symmetry-related to the diffuse nuclear scattering centered at the (1, 1/2, 0)-type positions arising from atomic short range order. The intensity of this diffuse magnetic scattering in all of the alloys decreases smoothly with temperature, approaching zero in the range 300 to 350°K. The spin-spin correlation range, as judged from the width of the magnetic diffuse peaks, also decreases smoothly with temperature. Neither the width nor the intensity of this magnetic scattering gives any hint of a freezing transition at lower temperatures.

Advances in neutron technology made during the past decade have permitted neutron inelastic scattering experiments to be performed with full polarization analysis. The power of this technique for the identification of components of dynamic spin fluctuations in magnetic systems is illustrated in this presentation by two experiments on the one-dimensional, X-Y antiferromagnet TMMC. In one experiment, spin fluctuations due to .pi.-solitons were measured for the first time and information was obtained on soliton-soliton collision processes. In the other, a theory which apparently described finite-energy magnetic excitations measured with unpolarized neutrons was shown to be deficient. Both of these experiments were carried out at the Institut Laue-Langevin in Grenoble, France. 13 refs., 8 figs.