Lorentz violation, gravitomagnetism, and intrinsic spin

A largely unconstrained set of relativity-violating effects is studied via the gravitomagnetic effect on intrinsic spins. The results of existing comagnetometer experiments are used to place constraints on two new combinations of these effects at the 10% level. We show that planned improvements in these experiments will make them competitive with the best existing sensitivities to this elusive class of relativity-violating effects. Prospects for measuring the conventional General-Relativistic gravitomagnetic effect are also considered.