Object in a magnetic field

Good afternoon,

I'm killian, I'm working on a model on Comsol which lets calculate the angular rate of an object in a uniform magnetic field over time. It's the same model as you migh have.
To make it simple, I assume the magnetic field is only in the z direction and that the object is spinning around the z direction. I give an initial value of the angular rate (900 rpm). I want to see how the angular rate of my object slow down over time.
The magnetic field should create a torque on the spinning object which should slow down.
I based my model on the magnetic brake that you can find on the Comsol website.
Unfortunatly, I obtain wrong result. My torque is equal to zero and my angular rate is decreasing infinitely.
Do you have an idea of a such result ? I think I have an issue with my magnetic field.
I obtained a model for a uniform magnetic field but when I use it in my model, solution doesn't converge.

Do you mind to tell me what you got from your model ?

Here is my email, it will be better to talk: mariek@my.erau.edu

Thank you for your help,

Killian