Ab initio theory of magnetic correlations in itinerant magnets

One of the challenging problems in modern magnetism is the description of the paramagnetic state because at finite temperatures the effect of spin fluctuation plays a fundamental role in altering the electronic structure. In magnetic metals, the magnetic properties are linked to the underlying spin-polarised electronic structure in a highly complex manner. In recent years, first-principles electronic structure theories based on the spin density functional (SDF) theory have been able to provide a quantitative account of many ground-state magnetic properties. In this article, the effect of spin fluctuation on the spin-polarised electronic structure and thus the magnetic properties will be discussed and its incorporation into ab initio calculations explained. If the magnetic and compositional ordering energies of magnetic metallic alloys are close, the compositional and magnetic correlations can profoundly influence each other. A theoretical formalism for treating these correlations within the framework of a first-principle electronic structure theory will be elaborated and the application to a number of magnetic alloys discussed and compared with experiments. (author)