Magnetoelastic Properties and Microstructure of Rare Earth/iron Compounds.

Available from UMI in association with The British Library. Requires signed TDF. The relationship between the magnetoelastic coefficients, microstructure, phase distribution and domain patterns has been studied for the pseudo binary material, Terfenol. Different techniques such as sintering, arc-melting and induction melting have been investigated to determine which of these methods produced the best material with the most consistent properties. Experimental rods have been characterised by making measurements of static and dynamic magnetoelastic coefficients and evaluating the coupling coefficient, k. The development of apparatus and measurement techniques is discussed and calculations of the magnetoelastic coefficients are explained and the experimental errors are analysed. Polished sections of this potentially very useful transducer material have been studied using various techniques and measurements made of grain size and phase distribution. Material present within the microstructure was identified using X-ray diffractometry and Scanning Electron Microscope techniques and the numerous phases were catalogued. In general it was found that the magnetoelastic performance of even the best material produced by arc melt and induction melt methods was only moderate when compared with material which had been prepared by more sophisticated techniques in the United States. However it was possible to identify those microstructural features which most influenced the performance and it was established that those samples which did exhibit high magnetostriction coefficients were characterised by having relatively large grains which were free of second phase material and other inclusions. The effects of annealing were investigated and it was found that any improvements which occurred were invariably acompanied by an increase in grain size and a redistribution of second phase material. Studies were made of the domain patterns in Terfenol using the Bitter colloid techique to try and obtain information about the nature of the magnetic domains and the changes which occur in the domain patterns as the bias field is increased through the region of optimum coupling.