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Postby TGTT23071246» Ferromagnetism Phenomenon

Explain the phenomenon of ferromagnetism

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The fact that iron vapor and iron ions in solution exhibit only paramagnetism suggests that the ferromagnetism of soils iron is a property, not of individual atoms, but of the crystals that make up a ferromagnetic of solid iron is a property, not of individual atoms, but of the crystals that make up a ferromagnetic material. In such materials, an interaction called exchange coupling (a quantum effect) couples the magnetic moments of adjacent atoms in rigid parallel alignment. Quantum physics successfully predicts from electrons configuration that the only elements for which this coupling will occur are Fe, Co, Ni, Gd, and Dy-just those elements for which ferromagnetism is observed.

The magnetic induction B in the iron core is made up of B0, due to the current in the copper winding plus BM, due to the current in the copper winding plus BM, the magnetic induction sue to the iron, plus BM, is magnetic induction due to the iron, which is proportional to the magnetization of iron. Often BM is much greater than B0. As the external magnetizing field is increased, saturation is observed as BM reaches its maximum value, corresponding to complete alignment of atomic moments in the iron. In the domain theory of ferromagnetism, one pictures the specimen as made up of domain microcrystal regions within which there is practically prefect alignment of atomic moments. But the vectors representing the moments in various domains are not parallel at low values of B0. When an external magnetizing field is increased in size, displacing their boundaries which are near parallel orientation with the field increase in size, displacing their boundaries at the expense in size, displacing their boundaries at the expense of other domains. At first this boundary displacement is reversible, but in stronger fields irreversible displacements occur. In still strong fields rotation of the magnetic moment within domains takes place, and saturation is reached when this completed.

The initial magnetization curve is not retraced as the magnetizing current in the toroid is first increased, then decreased. The lack of retrace ability is called hysteresis and it is associated with energy needed to reorient the domains. When the magnetizing field is made zero the specimen retains some “permanent” magnetism. The area of a hysteresis loop is a measure of the energy dissipated, as heat, in taking a specimen of unit volume through a magnetic cycle.
 

By TGTT23071246 on 1/4/2016 12:29:06 AM
TGTT23071246 on 1/4/2016 12:25:35 AM
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