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Non Life Sciences => Technology => Topic started by: flofelis on 04/04/2016 07:00:01

Title: Magnetization (M) / Magnetic Moment (m) of a NdFeB magnet~
Post by: flofelis on 04/04/2016 07:00:01

Hi All,

So, I am pretty new in the area of magnetism. Please pardon me for some questions that might be pretty fundamental and basic here.

I am trying to understand the difference between magnetic moment and magnetization. I thought I understood magnetization as the degree to which a magnet is magnetised, thus the amount of field present within it, as in the self induced magnetic field within the magnet itself. However, I am unsure as to how the magnetization affect the external of the permanent magnet... and then I thought magnetic moment would be the moment (i.e. the torque) onto the permanent magnet giving that amount of magnetization within it, so the magnetic moment and be related somewhat to the magnetization
 =S sorry, I hope I am not making this sound too confusing as I am pretty much confused myself.

 I would need to clarify my doubts in this as I need to find out the magnetization for a cylindrical NdFeB for a dynamic equation that I am working on. I understand that the NdFeB, a ferromagnetic material has a non-linear B-H relationship, thus it doesn't have a constant magnetization value. Nonetheless, is there anyway I could find out? I would like to assume that the region of operation I will work on is linear as the range of current supply is small (i.e. ~ +/-5A) but I am not sure if that makes sense.

 I look forward to any advice and suggestions =)
 Thank you!

Title: Re: Magnetization (M) / Magnetic Moment (m) of a NdFeB magnet~
Post by: evan_au on 04/04/2016 09:55:35

Quote

how the magnetization affect the external of the permanent magnet?

Many Ferromagnetic (http://en.wikipedia.org/wiki/Ferromagnetism) materials have a very strong internal magnetic field (within one tiny domain), but almost no external magnetic field, because adjacent domains are oriented in opposite directions, cancelling each other, and leaving almost no external magnetic field.

You only get a strong external field when most of the domains are aligned in their magnetic fields.
And it only stays like this if the magnetic material has a high coercivity (and it is kept well below the Curie temperature).

Quote

a cylindrical NdFeB

I am not sure what you are after, but reading between the lines...

I assume that this sample of NdFeB (http://en.wikipedia.org/wiki/Neodymium_magnet) is a permanent magnet?

Do you assume that it is at room temperature, and already has a strong external field?

• In this part of the H-M curve, increasing the field strength (H) considerably hardly changes the magnetization (M)
  
• In this case you might be using the 5A current as some form of actuator?
  
• ...And you want to find out how much the actuator current will affect the magnetic field of the permanent magnet?
  
• Or are you trying to remagnetize it in a different orientation?

Do you assume that it is at room temperature, and has no external field?

• In this part of the H-M curve, increasing the field strength (H) does changes the magnetization (M)
  but removing the external field leaves it with a considerable magnetization.

Or are you assuming that it is above the Curie temperature (around 400C), has effectively no magnetic field, and you wish to impose a field as the magnet cools?

• Above the Curie temperature, it ceases to be a ferromagnetic material
  

See: https://en.wikipedia.org/wiki/Magnetic_hysteresis