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Magnetism in disordered materials

Chrobak A.

Archives of Materials Science and Engineering

2012

Vol. 58, nr 2

80--109

Purpose: The paper is a review of some problems concerning micromagnetism and magnetism in disordered system.Magnetism of disordered systems is an important problem in analysis of many magnetic materials. As we understand, the term disorder is associated with the both structural (topological and/or chemical) and magnetic (interactions, anisotropy) failures. Typical materials, where phenomena are influenced by the disorder are amorphous and nanocrystalline alloys, nanostructures of magnetic objects, nanoconposites, diluted magnetic materials and intermetallic compounds of rare earth and transition metals. Moreover, in polycrystalline samples can be observed some anomalies related to the area between the grains, which inherently carries some attributes of the disorder. Thus, knowledge of the subject presented here is essential for the proper analysis of magnetics with elements of disorder. In the paper the following problems are discussed: i)magnetization processes in nanosized objects including the famous Stoner-Wohlfarth model, ii) superparamagnetism and magnetic viscosity (time dependent effects), iii) random field Ising model, random bond model and random anisotropy model. Applications of the theories for selected materials (magnetically soft and hard, thin layers, diluted magnetics, and powder systems) are also shown. Design/methodology/approach: Magnetism in disordered materials is a complex problem that, until now, has not exact solutions. There the two approaches. One of them requires some approximation of the problem in order to obtain exact analytical results. The second approach consists in numerical analysis of exact problem that leads to approximated solutions. In the both cases it is important in which stage of a model the disorder is introduced. In the paper the two approaches are widely discussed. Findings: The main conclusion of the paper is that some unusual magnetic properties can be attributed to magnetic and structural disorder. Practical implications: Application of the presented in the paper models indicate that in many magnetic materials the contribution of magnetic disorder plays an important role and should be taken onto account in order to perform correct analysis. Originality/value: The presented collection of different theoretical models including some elements of micromagnetism and magnetism in disordered system as well as applications of the theories to modern magnetric materials is an original idea. The paper is addressed to scientists and researchers that deal with magnetism and related subjects.