  We calculate the dependence of the nuclear magnetic moments on the quark
masses including the spin-spin interaction effects and obtain limits on the
variation of the fine structure constant $\alpha$ and $(m_q/\Lambda_{QCD})$
using recent atomic clock experiments examining hyperfine transitions in H, Rb,
Cs, Yb$^+$ and Hg$^+$ and the optical transition in H, Hg$^+$ and Yb$^+$ .
