الفهرس 
Experimental methodOnly 14 pages are availabe for public view
 |  | from | 166 |  |  |
| | | from | 166 | | |
Abstract
This dissertation is a result of a scientific co-operation between Physics Department. Faculty of Science, Tanta University and Physics Department of the Technical University of Denmark, in which the present work was carried out. In this thesis Mossbauer spectroscopy as the main investigation tool. has been used to study the magnetic properties of ultrafine magnetic particles, phase transformation of some selected materials, phase identification, surface effects and magnetic relaxation phenomena. The thesis consists of a number of studies. The common factor in these studies is that they all deal with the properties of ultrafine particles and systems of ultrafine particles. The studies are documented in the form of chapters. The first three chapters contain a brief introduction in which most of the concepts used in the later chapters are defined. The results are presented in chapters 4 to 10. Chapter 1: gives brief introduction to Mossbauer spectroscopy. Chapter 2: gives a short discussion of the experimental equipment, experimental techniques and the sample preparations. Chapter 3: gives a short introduction to some relaxation phenomena which are often met in Mossbauer spectroscopy studies of ultrafine particles. Chapter 4: Deals with particle interaction effects in systems of microcrystals of synthetic feroxyhite (6’- FeOOH). The superparamagnetic relaxation of ultrafine particles of synthetic feroxyhite (6’-FeOOH) have been studied . The behaviour of oleic acid coated and uncoated particles are compared. The effects of pressing of the sample are also investigated. The difference in the blocking temperatures of the three samples is explained by the different strength of the particle interaction. Measurements at 5 K in large applied magnetic fields parallel to the gamma ray direction showed that lines 2 and 5 did not vanish completely. This indicates the presence of spin-canting effects. The observed difference in the degree of canting of the three samples is explained by the difference of the interaction between the particles.