Hi Mohammadreza Arab ,

of course, the details depend on the geometry. In the simplest case, two ferromagnetic cuboids (e. g. two parts forming the core of an electromagnet) are separated by an air gap of length d, and there is a magnetic flux Phi through the cuboids and the air gap, the force is:

F = Phi2 / (2 * my0 * d)

Hello,

Generally you talk about torque that is not really a force but a force moment (torque = moment of a force). As you know there is rotational effect not really a translational effect due to a force such as in statics.

The vector product between a given field (e.g. the external bias field, the exchange field, the dipolar field) and the static magnetization of the ferromagnet

It has the dimension of an energy density and expresses a sort of force on the magnetization that precesses around the filed.

Greetings

Hello Israa,

I agree with you about the absence of a translational effect on dipoles in homogeneous fields but don't you think that inhomogeneous fields can exert a translational force on dipoles?

Hello Joerg,

Interesting question!

The nonuniformity of a field can cause also a translation effect due to its spatial gradient. Maybe the translation effect depends on the entity of the gradient but I think that the rotational effect is always prevalent.

Greetings

Jiles, D. C., and D. L. Atherton. "Theory of the magnetisation process in ferromagnets and its application to the magnetomechanical effect." Journal of Physics D: Applied Physics 17, no. 6 (1984): 1265.

hi Joerg Fricke

what does my0 in that formula mean?

Hi Mohammadreza Arab ,

I wasn't sure how to insert Greek characters in RG answers, so my0 stands for the permeability of vacuum = 4 * pi * 10^-7 H/m.