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Paramagnetism




Paramagnetism & Paramagnetic effect

  • Materials having non zero permanent magnetic moment may either be paramagnetic or ferromagnetic but in this section we will only discuss paramagnetic effects
  • Para magnetism occurs in material where the magnetic field produced by orbital and spin motion of the electron do not cancel each other completely
  • Materials showing paramagnetic effects in the presence of external magnetic field have permanent magnetic moment of the atoms
  • In the absence of external field paramagnetic material have magnetic moments but they are oriented randomly.
  • These moments (both due to spin and orbital motion of electron) experience an orienting effect in the presence of externally applied magnetic field
  • Due to this orienting effect material gets magnetized parallel to the external applied field resulting in positive paramagnetic susceptibility
  • This alignment of atomic magnetic moments in paramagnetic substance is opposed by the thermal motion of the atoms ,so alignment increases with the decrease in temperature and increase in strength of applied magnetic field
  • Thus there is a sharp dependence of paramagnetic susceptibility on temperature
  • For paramagnetic substance magnetic susceptibility is of the order of 10-5 to 10-3 and it is temperature dependent
  • When a paramagnetic bar is placed in the magnetic field , the magnetic flux density in it is greater than the magnetic flux density $B_0$ in the vacuum. Thus the relative permeability of the paramagnetic substances is slightly greater then 1.
  • The magnetic flux density due to magnetization is small but positive.
  • Paramagnetic substances are used in the measurement of low temperature.

Properties of Paramagnetism

  • A paramagnetic bar , suspended between the poles of a magnet shows opposite poles to those of the magnet in its end.
  • Paramagnetic substances have a tendency to move from weaker to the stronger parts in a non-uniform magnetic field.
  • Paramagnetic substances obeys Curie's law




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