How to calculate saturation magnetisation in GMR effect?

[majas]

Homework Statement

Hello everyone. This is my first post.
I'm working now on my laboratory report from GMR effect. I have to calculate the antiferromagnetic coupling for my multilayers. I have only resistance versus magnetic field graphs.

Homework Equations

I want to use the equation:
$J_{AF}=-\frac{\mu_0 M_S t}{4}H_S$
It's easy to find $H_S$, $\mu_0$ and t is given, and I need $M_S$.

The Attempt at a Solution

I have found equation $$H_S=\frac{K}{M_S},$$ but there is next unknown K, which is the anisotropy constant, and I'm not sure how it is for permalloy which the multilayers were made.

Thank you for your help.

 

[majas]

I found some data for permalloy, I will use it and maybe it will work.
http://www.cwscholz.net/projects/diss/html/node58.html