Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

What happens, when you are trying to magnetize some iron bar?

  1. May 23, 2007 #1
    I tried 1.000.000 on google and I didn't find nothing. So please help me. Thank you.
     
  2. jcsd
  3. May 23, 2007 #2
    Have you tried searching on "induced magnetization"? Surround the two words in quotes to make sure google searches on the phrase rather than the individual words. But do take a little care because you can't always trust what you find on the internet. Maybe one of the experts here can point you at a trustworthy source.
     
  4. May 23, 2007 #3

    ranger

    User Avatar
    Gold Member

    When the magnetic domains of the iron bar (or any material in general) come under the influence of a magnetic field; they realign. Causing the iron to have more apparent magnetic properties.

    http://hyperphysics.phy-astr.gsu.edu/hbase/solids/ferro.html#c4
     
  5. May 23, 2007 #4
    Ok, but is it possible that current will show up, right?
     
  6. May 23, 2007 #5

    ranger

    User Avatar
    Gold Member

  7. May 23, 2007 #6
  8. May 23, 2007 #7

    ranger

    User Avatar
    Gold Member

    I'm not sure I follow your logic here.

    The magnetic field is simply the area that is influenced by the magnetic force.
     
  9. May 23, 2007 #8
    Nope. It's just magetic interaction between the magnetic fields of the domains and the magnetic field of the permanent magnet.
     
  10. May 23, 2007 #9
    so you say that I can magnetize some iron bar without time-varying magnet, right?
     
  11. May 23, 2007 #10

    ranger

    User Avatar
    Gold Member

    If you read the first link I gave you. You'll see why the iron bar becomes magnetized in the first place without varying the magnetic field, if thats what you mean by "time-varying" magnet. Its all about the magnetic domains becoming realigned.
     
  12. May 23, 2007 #11
    And what makes the magnet to lose its magnetic property?
     
  13. May 23, 2007 #12

    ranger

    User Avatar
    Gold Member

    Magnets can be affected by the following:
    1) Forces that knock the domains out of alignment
    2) Temperature. The higher the temp, the faster 1) will occur. Extreme heat, exceeding the curie point, will immediately damage the magnetic. The curie point is a threshold temperature above which a magnetic material loses its magnetism.
    3) Very sharp blow may also do some damage.
    4) And since a magnetic field affects magnetic domains of materials, a strong nearby field may also do some realignment.
     
  14. May 24, 2007 #13
    and is the magnetic field inside conductor affects the electrons (makes them more excited)?
     
  15. May 24, 2007 #14

    ranger

    User Avatar
    Gold Member

    Electron motion in atoms produces the magnetic fields of permanent [ferro]magnet.
    Electrons get excited when they have kinetic energy due to thermal activity or when they are influenced by a potential difference/electric field.
     
  16. May 24, 2007 #15
    But are they are forced from their "own" magnetic field?
     
  17. Aug 21, 2009 #16
    Dear Ranger,

    I registered on this forum for the opportunity of thanking you for your links and helpful information.

    thanks and kind regards to all

    Wal
     
  18. Aug 23, 2009 #17
    Just a few comments -- hopefully helpful.

    1. As I'm sure the links state, applying a stong magnetic field to a ferrous material will magnetize the material. This is done because it forces all of the magmetic domains to align. In ferrous materials, once the external magnetic field us of suffcient strength, the domains will remailn aligned after it is gone. This is usually demonstrated with a diagram known as a hysterisis loop.

    2. To predictably demagnetize ferrous materials a variable field is used. A popular method is to apply a certain magnetic field in one direction followed by a field of half that intensity in the opposite direction. This pattern is repeated several times with each field half the intensity of the previous one. This effectively randomizes the domains. I think that in commercial demagnetizers, this is sometimes done by applying an ac field and slowly moving the demagnetizer away from the item being demagnetized.
     
  19. Aug 23, 2009 #18
    To demagnetise an iron magnet, you simply need to expose it to a magnetic field with the amount called "coercive field" in the opposite direction of the iron magnet's field. If you really want to understand this revise what's called "Hysteresis loop".

    As I can see you're not familiar with magnetism, and therefore I'm gonna oversimplify the problem for you.

    You can (of course you can't but as an oversimplification) divide materials into 2 types, paramagnetic and ferromagnetic, both are the same, but the only difference is the way they respond to magnetic field at a certain temperature.
    Materials like Aluminum are paramagnetic, but if you cool them to a certain temperature called critical temperature, they start to behave like iron (ferromagnetic).
    The difference between paramagnets and ferromagnets is that paramagnets can use the temperature's energy to minimise the magnetic field in order to minimise the energy of the system. Don't forget that all systems in the world want to minimise their energy, that's why everything falls from up to down, and that's why charges get attracted, and for the same reason magnets get attracted.
    When you apply a magnetic field to a paramagnetic material and ferromagnetic material, they both tend to align their spins in the direction of the magnetic field, with no difference at all (there is but not our consideration). The difference happens when you remove the magnetic field, where ferromagnetic material can't employ the temperature's energy to go back to the minimal magnetic field, while paramagnetic materials can.
    But this is not absolute statement, because in fact ferromagnetic materials keep trying to minimise their energy, but they take very long time, this is why they stay magnetised.

    I hope this helps, I know it's somehow complicated. If you have a question about what I've said, just ask.

    Good luck :)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?