Some materials exhibit a magnetization which is proportional to the applied magnetic field in which the material is placed. These materials are said to be paramagnetic and follow Curie's law:

M = CB/T

Where M is the magneticization, C is Curie's Constant, B is the applied magnetic field, and T is the temperature.

Atoms' electrons have a property called spin which creates an intrinsic magnetic moment. In addition the orbit of electrons can be viewed as tiny electric current loops. In most materials the total magnetic moment caused by the orbit term and the spin term cancel but in paramagnetic materials, the cancelation is incomplete.

As Curie's law indicates, in an external magnetic field these little atomic magnets will line up with the field. Curie's law is incomplete because it fails to predict what will happen when most of the little magnets are lined up (after everything is lined up, increasing the external field will not increase the total magnetization) so Curie's Constant really should be expressed as a function of how much of the material is already lined up.

Paramagnetic materials in magnetic fields will act like magnets but when the field is removed, thermal motion will mess up the magnetic alignment. In general paramagnetic effects are small (magnetic susceptibility of the order of 10-3 to 10-5).

Ferromagnetic materials above the Curie temperature become paramagnetic.

The following is a list of some paramagnetic elements and their magnetic susceptabilties:

  • Uranium: 0.0004
  • Platinum: 0.00026
  • Aluminum: 0.000022
  • Sodium: 0.0000072
  • Oxygen: 0.0000019
  • I put the values in decimal form so one can see just how small they are. For comparision, iron, a ferromagnetic material, has a magnetic susceptablility of about 1000!

    Paramagnetic materials are so weakly magnetic that the effects are negligible except in very large fields of several teslas. The effect, once it becomes noticeable, is a very slight attraction in the direction of the field. A material that is very slightly repelled by a magnetic field is diamagnetic.

    Par`a*mag*net"ic (?), a. [Pref. para- + magnetic.]

    Magnetic, as opposed to diamagnetic.



    A paramagnetic substance.


    -- Par`a*mag*net"ic*al*ly (#), adv.


    © Webster 1913.

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