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## Homework Statement

Calculate magnetisation for partition function

##Z=12+4\cosh (8\beta J)## for Ising model 2x2 lattice.

## Homework Equations

[tex]F=-k_BTln Z[/tex]

[tex]M(H,T)=-\frac{\partial}{\partial H}(\frac{F}{k_BT})[/tex]

## The Attempt at a Solution

For me it looks that magnetisation is zero. By just doing the derivatives. But solution of problem is ##\frac{16+8e^{\beta J}}{Z}##. If I combine relation from relevant equation it looks like for me that solution is zero. Where I making the mistake.