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Title: Grain size effects in polycrystalline exchange biased systems
Author: Vallejo Fernandez, Gonzalo
ISNI:       0000 0001 3542 0062
Awarding Body: University of York
Current Institution: University of York
Date of Award: 2006
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The capability of a novel sputtering technology known as HiTUS to produce thin films with controlled grain size and distribution has been evaluated. This has been achieved for different materials chosen due to their importance in industrial applications. The grain size of the deposited films was measured from TEM images in bright field mode. All the distributions were lognormal and over five hundred particles were measured to recompose each lognormal function. For a range of materials close control of grain size between 4nm and 30nm was achieved. The grain size was controlled through the deposition rate. This has allowed the investigation of the effect of the antiferromagnetic grain size on exchange bias without the use of underlayers, additives or substrate heating. It was found that the magnitude of the loop shift strongly correlated to the distribution of grain volumes in the antiferromagnetic layer. Using detailed measurements of the grain size distribution the features of exchange bias in these systems can be explained on the basis of a grain volume model with coherent rotation. For example using measurement protocols that ensure reproducibility of data has allowed the development of a new measurement technique for the anisotropy constant of metallic antiferromagnets. This is a key result since the anisotropy is used in all theoretical models of exchange bias as a fitting parameter. The anisotropy was determined only from experimental features and only its temperature dependence had to be assumed to be of the form K(OK)(1-T/TN)3 in order to calculate the values. For IrMn K(293K) =4.14xlO6erg/cc and for FeMn K(293K) = 1.36x106erg.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available