Introduction

Amorphous magnets constitute a class of systems with the highest level of disorder. The key to the difference between crystalline and noncrystalline solids is that no two atomic sites are equivalent in amorphous substances, whereas all macroscopic directions may be equivalent in the bulk. This chapter presents general information and definitions about the natures of the three categories: ferromagnet, ferrimagnet and canted ferrimagnet. In an amorphous ferromagnet the spins are all oriented in the same direction but the topological arrangement of spins is not regular. The coupling of magnetic moments in amorphous magnets, as in most other magnetic materials, is due to the exchange interaction. The Hamiltonian is a very attractive one to use as a starting point for calculating the physical properties of amorphous magnets. The amorphous insulating magnets due to superexchange interactions seems to be nearly speromagnetic, which have no counter examples in the crystalline phase, such as a natural ferric hydroxide gel.