磁性材料简介磁性材料的种类以及其形成机制.ppt

Diamagnetism Paramagnetism Ferromagnetism Antiferromagnetism Others Diamagnetism ? PARAMAGNETISM Paramagnetic materials exhibit magnetisation according to Curies Law: where M is the resulting magnetisation; B is the magnetic flux density of the applied field, measured in tesla; T is absolute temperature, measured in kelvins and C is a material-specific Curie constant. Metal Ferromagnetism  Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. Historically, the term ferromagnet was used for any material that could exhibit spontaneous magnetization: a net magnetic moment in the absence of an external magnetic field. This general definition is still in common use. Antiferromagnetism In materials that exhibit antiferromagnetism, the spins of magnetic electrons align in a regular pattern with neighboring spins pointing in opposite directions. This is the opposite of ferromagnetism. Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Neel temperature. Above the Neel temperature, the material is typically paramagnetic. Antiferromagnets can also couple to ferromagnetic materials through a mechanism known as exchange anisotropy, in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligning magnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of the antiferromagnet. This provides the ability to pin the orientation of a ferromagnetic film, which provides one of the main uses in so-called spin valves, which are the basis of magnetic sensors including modern hard drive read heads. ? FERROMAGNETIC ORDER ? FERROMAGNETIC DOMAINS ? SINGLE DOMAIN PARTICLES ? FERROMAGNETIC DOMAINS The directions of magnetization of different domains need not be parallel. An arrange