How to calculate the magnetic dipole moment?

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Discussion Overview

The discussion revolves around the calculation of the magnetic dipole moment of a bar magnet or any type of magnet, exploring various methods and considerations without relying on a specific formula.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests determining the pole strength of the magnet and using the relationship μ = md, where d is the separation between the poles, but expresses uncertainty about calculating pole strength in A.m.
  • Another participant proposes that calculating the magnetic dipole moment from first principles is complex, especially at different temperatures, mentioning the need for a mean field approximation and the impact of grain boundaries on the calculation.
  • A different approach is suggested, where one could measure the force exerted by the magnet on a current loop of known magnetic moment to determine the magnetic field B and subsequently calculate the necessary pole strengths.
  • Participants discuss the measurement of the magnetic field, noting a specific value of 0.3426T, but there is confusion regarding the location of this measurement, referred to as point "r."

Areas of Agreement / Disagreement

Participants express differing views on how to approach the calculation of the magnetic dipole moment, with no consensus on a single method or solution. Uncertainties about the definitions and measurements involved are evident.

Contextual Notes

There are limitations regarding the assumptions made about temperature effects, the presence of grain boundaries, and the definitions of pole strength and magnetic moment, which remain unresolved.

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How to calculate the magnetic dipole moment??

Does anyone out there know how I can calculate the magnetic dipole moment of a simple bar magnet?
Or any kind of magnet?

Without using this formula: \tau = μ x B
 
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I think that I need to figure out the pole strength (m1, m2) of the magnet and them figure out the moment.

I think, the magnetic dipole moment is μ = md
d= separation between the two poles?

I'm not sure though...
IN FACT, how can anyone calculate the pole strength in A.m?
 
Do you mean calculate from first principles? I don't think that's easy. At zero temperature, if there are no grain boundaries, you could probably add up all the dipole moments from all the atoms. If it's ferromagnetic, I think they line up.

At higher temperature, you need to calculate the occupancy of aligned versus non-aligned spins. I guess it takes a Boltzmann distribution for each atom, but they are coupled so you need some kind of mean field approximation or something.

But if there are grain boundaries, that kinda screws up everything.
 
Khashishi said:
Do you mean calculate from first principles? I don't think that's easy. At zero temperature, if there are no grain boundaries, you could probably add up all the dipole moments from all the atoms. If it's ferromagnetic, I think they line up.

At higher temperature, you need to calculate the occupancy of aligned versus non-aligned spins. I guess it takes a Boltzmann distribution for each atom, but they are coupled so you need some kind of mean field approximation or something.

But if there are grain boundaries, that kinda screws up everything.

Well would anyone calculate the magnetic moment and the magnetic pole strength?
μ = ?
m1= ?

What way can I figure out the magnetic moment/magnetic pole strength.
 
You can measure the force the magnet exerts on current loop of known magnetic moment, use the formula for magnetic force to determine the magnetic field B the magnet produces, and then calculate what poles are needed to produce such field.
 
The magnetic field B is already given.
I only need to calculate the moment.
 
In what way is the magnetic field given?
 
The magnetic field is measured by an instrument.
Its at 0.3426T
 
At which point?
 
  • #10
At point r.
 
  • #11
Can you post a drawing? I do not know where "r" is.
 

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