Can you give a basic explanation of what is crystal field anisotropy ?
What is the reason to arise ?
In spin ice it forces the dipoles to point in the local 111 direction.
For partially filled rare earth atoms hund rule requires S and L max. This leaves (2s +1)(2l+1) degeneracy which is partially lifted from the LS coupling. When inserted in anisotropic field inside crystal the expectation value , or mean value of L is 0 = 0 and the L is quenched leaving only S so is forced to point in some local direction, but this is if the field removes the deneracy ?
Is it this or it is much more complicated ?