Hi, I'm having a bit of trouble understanding the third part of q4 in the 2013 paper.
The question says that the interaction hamiltonian for a single ion is H = - g*mu(B)*J*B. It the asks to find the average magnetic moment [mu(z)] (i tried to use the arrow brackets but it disappears in the preview) and show it follows the curie law and equal ~ C/T
Basically I'm not sure how to approach this. If I take the hamiltonian as it is I can get an expression through working it out from the partition function and stuff.
But since it asks for an average magnetic moment, I thought maybe the question requires mean field theory, and the total hamiltonian should include the spin-spin interaction term? I would've thought the question would include that though.