| Themes > Science > Physics > Solid State Physics > Magnetic Properties of Solids > Diamagnetism and Paramagnetism > Diamagnetism and Paramagnetism |
All matter exhibits magnetic properties when placed in a magnetic field, and matter may be classified according to its interaction with this magnetic field. The more obvious manifestations of magnetic interactions between a magnetic field and matter may be seen in the workings of compass needles and iron's attraction to bar magnets. This type of interaction, characteristic of ferromagnetic materials, will be discussed later. For now, we focus on two of the more subtle types of magnetism--diamagnetism and paramagnetism. Diamagnetic is a classification used to describe materials that line up at right angles to a nonuniform magnetic field and are slightly repelled by that field. Diamagnetism occurs as a result of a magnetic field's interference with the motion of electrons orbiting the atoms or molecules of an element or compound. When matter is placed in a magnetic field, the magnetic force acts upon the moving electrons in the matter, causing the electrons to be deflected in ways that speed up some electrons and slow down others. This movement of the electrons interferes with the motion of the magnetic field, so the atoms internally oppose the field. This causes the material to be slightly repelled by the magnetic field. Diamagnetism is characteristic of elements and compounds that possess complete sets of valence electrons--meaning that all their electrons are paired. Electrons orbit an atom while spinning on their own axis. If a spinning electron is orbiting singly, this charge movement generates a magnetic field. However, two paired electrons have opposite spins--meaning that the magnetic field generated by each electron is canceled out by the magnetic field of the other electron. So when all of an atom's electrons are paired, the opposite spins of the electrons cancel each other out and cause the element to have no magnetic field. When this element is then placed in a magnetic field, it is repelled. All materials demonstrate a degree of diamagnetism. In some substances, however, other magnetic properties may mask its diamagnetic properties. Paramagnets, another classification of matter, are one example of one magnetic property masking the diamagnetic property. Paramagnetism generally occurs in elements or compounds possessing unpaired electrons. Many compounds containing iron, palladium, platinum, and the rare earth elements have single electrons that generate a small magnetic field. In these cases, the atom acts as a small permanent magnet. If a substance containing such atoms is placed in a magnetic field, the field of the atom aligns with the field of the applied magnetic field and causes the atom to be slightly attracted to that magnetic field. This attraction to an applied magnetic field is known as paramagnetism. |
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