A magnetic domain describes a region within a magnetic material which has uniform magnetization. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When heated above a temperature called the Curie temperature, a piece of ferromagnetic material undergoes a phase transition, and the uniform magnetization within a domain spontaneously disappears: each atom has its own direction of magnetic moment, independent from its neighbouring atoms. Magnetic domain structure is responsible for the magnetic behavior of ferromagnetic materials like iron, nickel, cobalt and their alloys, ferrites etc. The regions separating magnetic domains are called domain walls, where the magnetisation rotates coherently from the direction in one domain to that in the next domain.