magnetism
Magnetism is the force effect between magnetized materials(magnets). Each elementary particle of materials has a magnetic moment called spin. Magnetization of a material is the parallel alignment of the magnetic moments of the individual molecules of a material.
Normally, in ferromagnetic materials, e.g. iron, nickel, cobalt, there are districts of parallel aligned domains, the Weiss districts. Under the influence of a magnetic field, the Weiss domains arrange themselves in parallel, and the material thus becomes a magnet. Magnetism does not disappear when the external magnetic field is turned off. Magnetism is characterized by the magnetic field (H-field). The field lines run outside the magnet from the north pole to the south pole, inside the magnet from the south pole to the north pole.
The magnetic field strength, given in amperes per meter (A/m), and the magnetic flux density(Tesla) describe the strength of a magnetic field. The product of the current and the number of turns of a current-carrying coil is the magnetic flux density. The magnetic flux density is used to calculate the induced voltage( induction) and the Lorentz force. Permeability serves as a material-dependent conversion factor between the two field quantities. The strength of magnetic fields can be measured with Hall probes. The space in which a magnetic field propagates is the magnetic circuit.
Besides magnetic materials, magnetic fields are also caused by electric currents. Magnetic forces occur in a conductor through which a current flows. This electromagnetism is used in many ways in electrical engineering, e.g. in electromagnets, motors, transformers and data storage. Electromagnetic fields can also propagate in space as electromagnetic waves.
In many areas of technology - from motor vehicles to personal computers(PCs) - it is impossible to imagine life without magnetic materials. This also applies to applications in magnetic sensor and information technology. Here, for example, the discovery of the GMR effect(Giant Magneto-Resistive) has made it possible to significantly increase the storage density ofhard disks.