I How Does a Vibrating Sample Magnetometer Calculate Magnetic Moment?

[no_einstein]

TL;DR

How do you find the change in flux with respect to position

In descriptions of a VSM, the induced voltage in a coil is shown to be emf = -dPhi/dt = - (dPhi/dz)(dz/dt). From here, everyone seem to jump to a solution of emf = 2*Pi*A*f*m*sin(2*Pi*f*t).
That makes some sense: in this case, you can define z = A*cos(2*Pi*f*t) so (dz/dt) = 2*Pi*A*f*sin(2*Pi*f*t). I'm confused why (dPhi/dz) turns out to be equal to or proportional to m (the magnetic moment). Is it an approximation that assumes a small amplitude of oscillation and so a linear dependence of the magnetic flux on z? I am having trouble picturing this. Can someone help?

 

[vanhees71]

What is a "VSM"? Is it a rotating coil in a magnetic field?

 

[berkeman]

What is a "VSM"? Is it a rotating coil in a magnetic field?

I guess it's his Vibrating Sample Magnetometer -- a quick search of Google Images turns up this:

https://en.wikipedia.org/wiki/Vibrating-sample_magnetometer