I've derived the matrix using two different, but equivalent methods (the one described in the above link-Sakurai and by calculating the direct products of Pauli matrices) and it came out the same, yet its eigenvalues are not what I know they must be, so there must be something fundamentally...
Hi o:)
I wasn't able to insert equations here, so here's the link where my problem is described:
http://www.advancedphysics.org/forum/showthread.php?t=7696