The discussion focuses on calculating the magnetic dipole moment of a bar magnet without using the torque formula \(\tau = \mu \times B\). Participants suggest determining the pole strength (m1, m2) and using the formula \(\mu = md\), where \(d\) is the separation between the poles. They highlight the complexity of calculating pole strength, especially at varying temperatures and the presence of grain boundaries. A practical method mentioned involves measuring the force exerted by the magnet on a current loop and using the known magnetic field strength of 0.3426T to derive the magnetic moment.
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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.