Ferro Magnetism

Ferro magnetism comes from the term ‘ferrous’ meaning iron, the first type of metal discovered to exhibit attraction to magnetic fields.?Ferromagnetism?is the basic method in which a compound forms a permanent magnet or is attracted to a magnetic field.?In?a nonmagnetic compound, permanent magnetic dipoles tend to line up antiparallel in order to cancel each other out. In ferromagnetism, however, the opposite is true. Ferromagnetism arises from the spontaneous lining up of? permanent dipole?parallel to each other within a compound. These magnetic dipoles arise from the movement of pairs of electrons within their atomic orbitals.

Ferromagnetism is normally seen in materials that have partially filled outer valence shells. Ferromagnetic materials exhibit parallel alignment of moments, resulting in large net magnetization even in the absence of a magnetic field. However, this aligning of magnetic moments does not mean that a ferromagnetic compound is magnetic itself. Although in ferromagnetic compounds the permanent dipoles line up with each other, they do so in domains. Throughout the bulk of the material, the dipoles line up in sections or domains. These line up opposite to each other, meaning that the overall magnetic moment throughout the material is zero. Elements such as Fe, Ni, and Co and alloys that exhibit?Relative permeability?up to 104?are well known ferromagnetic materials.

In ferromagnetic substances within a certain temperature range, there are net atomic magnetic moments that line up in such a way that magnetization persists after the removal of the applied field. Below a certain temperature, called the?curie point?an increasing magnetism applied?to a ferromagnetic substance will cause increasing magnetization to a high value called the?saturation. This is because a ferromagnetic substance consists of small magnetized regions called domains. The total magnetic moment of a sample of the substance is the vector sum of the magnetic moments of the component domains.

?In order to induce permanent magnetism, a ferromagnetic compound must be placed within a strong magnetic field. Once in the magnetic field, the domains line up parallel to generate one strong magnetic moment. It is known for some materials that the domains remain in this position even when the?External magnetism?is removed. The ability of some materials to remember this ‘magnetic history’ is called?hysteresis. Since energy is required for the reformation and saturation of the domains, there is a hysteresis in the magnetization field curve (hysteresis loop).