Heusler alloys

Abstract

In 1903 F. Heusler reported that it was possible to make ferromagnetic alloys from non-ferromagnetic constituents copper-manganese bronze and group B elements such as aluminium and tin. Further investigations showed that the magnetic properties of these alloys are related to their chemical, L21, structure, and to the ordering of the manganese atoms on an f.c.c. sublattice. Heusler alloys are properly described as ternary intermetallic compounds and they can disorder in a variety of ways. A review is given of the effects of disorder on the intensities of superlattice lines, and of the use of x-ray and neutron diffraction to determine quantitatively the extent and types of long-range chemical and magnetic order in Heusler alloys. As Heusler alloys exhibit most of the properties of metals but have the structure of an ordered compound, it is possible that several different magnetic exchange mechanisms may be operating. A review is given of the principal theories that have been employed to explain their magnetic properties, and some of the more recent results are discussed in terms of the generalized molecular field theory.