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The question is slightly deceiving however still simple for those academics therefore, here I present my question:

If I take a para-magnetic material and put it very close to a homogeneous magnetic field, the para magnetic material will start to accelerate towards the magnetic body thus it has kinetic energy (but I ensure it does not hit the magnet and stop it with my fingers) so does the magnetic field or body loose it magnetism or will the same magnetism stay? Because in Wikipedia, it says:

Energy is needed to generate a magnetic field both to work against the electric field that a changing magnetic field creates and to change the magnetization of any material within the magnetic field

However I'm sure that para-magnetic materials are not magnetized, so where is this energy coming from? Or is my understanding wrong if so can someone link me to a good website which uses mathematics and theory to show how para magnetic material works?

Thanks!

Ali
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2 Answers2

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A paramagnetic material is something that has a magnetic field even without the presence of an external field, but the external net effect is roughly zero. The internal atoms or molecules of the substance have magnetic diopoles meaning the substance itself is made up of billions of tiny magnets. The thing with paramagnetic materials is these dipoles are not lined up so their fields are oriented randomly making their overall field cancel out.

When an external field is applied, these internal dipoles suddenly align with the external field and create a net magnetic moment in the direction of the applied field. Whether you let the materials touch or hold them apart it doesn't change the energy of the magnetism which is built into the structure of the substance.

Note the illustration of the magnetic moments of the atoms or molecules in the structure of this paramagnetic material:

dipoles

Before the field is applied they are pointing randomly so there is no natural net magnetic field. Then the external field is added and they rotate to line up. When it is removed the field returns to zero (in a pure para-magnetic material). In some materials the atoms or molecules will self-align and remain magnetic after the field is removed resulting in ferromagnetism (permanent magnets) or antiferromagnetism.

If you want to dig even deeper the concept of the magnetic dipole is related to the more fundamental quantum mechanics of electron spin and angular momentum (EDM or electron dipole moment).

user6972
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  • From Wikipedia: Paramagnetic materials ... These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. This contradicts your first sentence. Wikipedia is saying that paramagnetic material has magnetic properties only in a magnetic field. – LDC3 Jul 20 '14 at 17:30
  • Thanks You, so no energy is lost but then what is the kinetic energy and where does it go due to the material trying to attract towards the magnet? –  Jul 20 '14 at 18:03
  • @LDC3 Read what I wrote more carefully. – user6972 Jul 20 '14 at 19:05
  • @RohanVijjhalwar when the material moves towards the magnet the field interaction (magnetic moment) is reduced slightly by the relative motion -- like an object falling in a gravity field. So you're taking kinetic energy out of the field (potential energy) until the material is held stationary again and the relative motion has stopped restoring the field's potential energy. – user6972 Jul 20 '14 at 19:09
  • @user6972 Ok, your statement (in it's entirety) is correct, but since I had trouble with it, you should change it. – LDC3 Jul 20 '14 at 19:14
  • @LDC3 There are materials that are considered paramagnetic that have been exposed to external fields turning them slightly magnetic when the field is removed. I think that sentence is accurate and is only confusing if you only read the first part of the wikipedia article. You'll note further down they contradict themselves when discussing paramagnetic effects like ferromagnetism, and curie temperatures. – user6972 Jul 20 '14 at 19:21
  • @user6972 Your first sentence indicates that paramagnetic material has a magnetic field (which it shouldn't) and then you say it's net effect is zero. I don't think you would have a magnetic field from a paramagnetic material without an external magnetic source. I understand that the magnetic domains are randomly oriented so that there is no magnetic field. This is why your first sentence should be changed. It should not say that paramagnetic material has a magnetic field, but that the paramagnetic material has randomly oriented magnetic domains. – LDC3 Jul 20 '14 at 20:05
  • @user6972 Quick Question, What if the object is turned into light using $E=mc^2$ then this light would escape without giving the magnetic potential energy then would the magnetic field's potential energy be decreased over time? –  Jul 21 '14 at 01:03
  • @RohanVijjhalwar the potential energy is always there in the atoms or molecules in the form of the electron spin and angular momentum. If you annihilate the electron you're converting all its mass related energy and there is no electron left to have a magnetic moment. – user6972 Jul 21 '14 at 01:48
  • @user6972 That in mind now, would the permentant magnet loose its magnetism as a result of my action of turning the object (paramagnetic material) into light ? Also very much thanks for teaching something new! –  Jul 21 '14 at 10:11
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    @RohanVijjhalwar Since it is no longer matter, there is nothing left to be magnetic. – user6972 Jul 25 '14 at 04:22
  • @user6972 But we are not converting the magnet into light, we are converting the PARAMAGNETIC material NOT the magnet. so does the MAGNET loose any of its energy. But im sure the MAGNET would loose no magnetism tho but just clarifying with you. But thanks Im learning something new. –  Jul 25 '14 at 13:41
  • @RohanVijjhalwar mater is matter whether in a magnetic state or paramagnetic state or non-magnetic state. Your string of questions don't really make sense and differ from your original question. Can you think about the specific situation and ask this again as a new question with perhaps some researched background to explain what you are asking about? – user6972 Jul 25 '14 at 16:47
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In a homogeneous field, the paramagnetic material does not move - why should it? An acceleration towards permanent magnets just happens as their field is not homogeneous. You (partially) align the magnets in the paramagnetic material with the magnetic field and bring them closer together, this releases energy. If you want to separate the objects again, you have to put in energy. However I'm sure that para-magnetic materials are not magnetized They get magnetized by your permanent magnet.

Murtuza Vadharia
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