In a hypothetical EPR experiment, a free La atom would first be subjected to an external magnetic field. Due to the Zeeman effect, this would lift the degeneracy of the energy levels in the atom. The strength of the effect will depend on the g-factor and on the strength of the applied magnetic field.
Then, the system will be irradiated by microwave radiation. The photons will be absorbed, but only transitions where |Δmj|=1 will be allowed in EPR, due to selection rules. Each of these transitions correspond to a rotation of the total magnetic moment. A 180° flip is possible in an increasing number of steps depending on the J of the level.