First quantitative investigations of electric and magnetic phenomena were done by Charles-Augustin de Coulomb (1736-1806). Their unified description is the work of James Clerk Maxwell (1831-1879). Maxwell's equations describe electric and magnetic fields on a macroscopic length scale. However, on an atomic length scale quantum theory has to be used for the proper microscopic description of the physical properties of matter.
The investigation of magnetization processes in fine ferromagnetic particles is on a somewhat intermediate level. On the one hand the size of the particles is in the order of nanometres or micrometres. Thus, the effects of magnetic domain formation have to be included in the physical model and Maxwell's equations will not be sufficient for a realistic description.
On the other hand effects which originate from the atomic structure of solids have to be considered. Magnetocrystalline anisotropy for example is caused by the crystal lattice, the periodical positions of atoms which compose the solid. Moreover the exchange interaction between the spin momentum of electrons is a typical quantum mechanical effect.
In purely quantum mechanical models, the size of the particles exceeds the size of systems which can be handled with today's computing power. Therefore, the only way is to `neglect' quantum mechanics, ignore the atomic nature of matter, and use classical physics in a continuous medium.
Such a classical theory started with a paper by Landau and Lifshitz in 1935 on the structure of the domain wall between two antiparallel magnetic domains. William Fuller Brown contributed several works and gave this theory the name micromagnetics. He wanted to emphasize the fact, that this theory should describe the details of the walls which separate magnetic domains as opposed to domain theory which considers the domains, but neglects the walls in between. Still, the microscopic details of the atomic structure are ignored and the material is considered from a macroscopic point of view by taking it to be continuous.