Ab initio study of magnetic anisotropy of M-type hexaferrite thin films

Ferrites are a broad class of oxide materials with a wide range oftechnologically important applications. The M-type hexaferrites, ofwhich BaFe12O19 is taken as a prototype compound, show particular promise as very high density magnetic and magneto-optical datastorage media. There are still serious gaps in the understanding ofthe fundamental origins of, and mechanisms governing, the magneticproperties of these materials. The detailed relationships between theseproperties and the material structure over nanometre length scales arealso not fully understood. This thesis addresses both of these pressingissues. It describes first a detailed ab initio theoretical treatment ofthe origins and magnitudes of the two most important mechanismswhich give rise to magnetic anisotropy, namely dipolar interactionsand single-ion contributions. The thesis outlines the theory of thesetwo types of magnetic interactions in solid insulating oxide materials.It also describes the theory of the deposition and growth of thin films,and the implementation of both branches of this theoretical studyin a set of original computer programs developed and refined duringthis study, comprising tools for both calculation and visualization. Anovel growth model and efficient Monte Carlo techniques are used toinvestigate and quantify the dependence on growth conditions of thestructure of thin films of hexaferrite materials. The magnetic theory is also implemented in a flexible and powerful program, which isused in turn to comprehensively investigate the structural dependenceof magnetic properties in the bulk crystalline material, idealized thinfilms, and finally by the simulated grown films. The influence of filmstructure on volume and surface contributions to the anisotropy ofthin films is thereby quantified and discussed.

Level dc:type.qualificationlevel

Doctoral (Level 8)

Year dc:date.issued

2001

Author dc:creator

• Kirk, SR

Language dc:language

en

Identifier

oai:salford-repository.worktribe.com:1326445

OAI identifier oai:identifier

oai:salford-repository.worktribe.com:1326445