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2015-08-29T08:31:27+08:00

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              Macroscopic magnetism is most common in ferrous materials, but everything has magnetic fields. At the atomic scale, electrons have something analogous to angular momentum called spin. In addition, the electrons are moving around the atom. Both spin and electron orbits generate a small magnetic dipole for every atom. However, electrons fill orbitals in pairs, one up and one down. When outer electron orbitals are unpaired, it is ferromagnetic. When the orbitals are full, the net dipole moment of the electrons cancels out. When an atom with unpaired electrons is placed in a magnetic field, the atom experiences a force and lines up. An object is magnetic at the macroscopic scale when the constituent atoms have their poles aligned by a magnetic field. The tiny net magnetic field of each atom being aligned in the same direction generates the magnets we are familiar with.
           There is no special magnet for non-ferrous materials. There is only one kind of magnetism. In order to be affected by a static magnetic field, an object needs to have a magnetic moment (i.e., N and S poles). When a ferromagnetic material is placed in a magnetic field, it develops these poles. We say that it is easily "polarized". Other materials can be polarized, but the response is much weaker. One can, for example, levitate a frog in a strong magnetic field.   In the presence of magnetic fields, the non-magnetic material magnetize.
        There are three types of magnetization: ferromagnetism, paramagnetism and diamagnetism. The most interesting example is ferromagnetism. Non-magnetized iron (latine ferrum) is composed of small domains - domains are little parts of material that act like small magnets, but since domains' magnetic fields are oriented in different directions, net magnetism of non-magnetized iron bar is about zero. In presence of magnetic field, these domains align themselves in the direction of outer magnetic field, therefore, non-magnetized material becomes itself a little magnet. And two magnets attract each other with opposite poles.
 


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