Hysteresis

   When a [1]ferromagnetic material is magnetized in one direction, it will not
   relax back to zero magnetization when the imposed magnetizing field is removed.
   It must be driven back to zero by a field in the opposite direction. If an
   alternating magnetic field is applied to the material, its magnetization will
   trace out a loop called a [2]hysteresis loop. The lack of retraceability of the
   magnetization curve is the property called hysteresis and it is related to the
   existence of [3]magnetic domains in the material. Once the magnetic domains are
   reoriented, it takes some energy to turn them back again. This property of
   ferrromagnetic materials is useful as a magnetic "memory". Some compositions of
   ferromagnetic materials will retain an imposed magnetization indefinitely and are
   useful as "permanent magnets". The magnetic memory aspects of iron and chromium
   oxides make them useful in audio [4]tape recording and for the magnetic storage
   of data on computer disks.
   [5]Index

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                                    Hysteresis Loop

                                     [hyloop.png]

   It is customary to plot the [10]magnetization M of the sample as a function of
   the [11]magnetic field strength H, since H is a measure of the externally applied
   field which drives the magnetization .

                           [12]Further discussion of concept

                         [13]Hysteresis in magnetic recording

                          [14]Variations in hysteresis curves

                             [15]Coercivity and remanence

   [16]Index
   Reference
   [17]Young
   Sec 29-8

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                           Hysteresis in Magnetic Recording

   Because of [22]hysteresis, an input signal at the level indicated by the dashed
   line could give a magnetization anywhere between C and D, depending upon the
   immediate previous history of the tape (i.e., the signal which preceded it). This
   clearly unacceptable situation is remedied by the [23]bias signal which cycles
   the oxide grains around their hysteresis loops so quickly that the magnetization
   averages to zero when no signal is applied. The result of the bias signal is like
   a magnetic eddy which settles down to zero if there is no signal superimposed
   upon it. If there is a signal, it offsets the bias signal so that it leaves a
   remnant magnetization proportional to the signal offset.

                                      [hyrec.png]

                                [24]Magnetic Recording

   [25]Index

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                            Variations in Hysteresis Curves

   There is considerable variation in the [30]hysteresis of different magnetic
   materials.

                                   [hystcurves.png]

   The curve on the left above represents materials which are sometimes called
   magnetically "hard". This includes various steel alloys and special alloys such
   as Alnico. If magnetized near saturation, such materials may retain a
   [31]magnetic field as high as B = 1 Tesla, corresponding to an internal
   [32]magnetization M = B/µ[0] of about 800,000 A/m.

   The curve on the right represents magnetically "soft" materials such as soft iron
   which are used for [33]transformer and [34]motor cores. They minimize the energy
   loss and heating associated with periodically reversing the magnetic field in AC
   electrical applications.
   [35]Index
   Reference
   [36]Young
   Sec 29-8
   [37]Hysteresis wiki

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References

   1. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/ferro.html#c1
   2. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c2
   3. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/ferro.html#c4
   4. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape.html#c1
   5. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
   6. http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
   7. http://hyperphysics.phy-astr.gsu.edu/hbase/solcon.html
   8. http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon
   9. Javascript:history.go(-1)
  10. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/magpr.html#c1
  11. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfield.html#c1
  12. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c1
  13. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c3
  14. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c4
  15. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/magperm.html#c1
  16. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
  17. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1
  18. http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
  19. http://hyperphysics.phy-astr.gsu.edu/hbase/solcon.html
  20. http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon
  21. Javascript:history.go(-1)
  22. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c1
  23. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape.html#c3
  24. http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape.html#c1
  25. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
  26. http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
  27. http://hyperphysics.phy-astr.gsu.edu/hbase/solcon.html
  28. http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon
  29. Javascript:history.go(-1)
  30. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/hyst.html#c1
  31. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html#c1
  32. http://hyperphysics.phy-astr.gsu.edu/hbase/Solids/magpr.html#c1
  33. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html#c1
  34. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indmot.html#c3
  35. http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
  36. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/eleref.html#c1
  37. https://en.wikipedia.org/wiki/Hysteresis
  38. http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html
  39. http://hyperphysics.phy-astr.gsu.edu/hbase/solcon.html
  40. http://hyperphysics.phy-astr.gsu.edu/hbase/emcon.html#emcon
  41. Javascript:history.go(-1)