We examine the phase and the period of the radiation-induced
oscillatory-magnetoresistance in GaAs/AlGaAs devices utilizing in-situ magnetic
field calibration by Electron Spin Resonance of DiPhenyl-Picryl-Hydrazal. The
results confirm a f-independent 1/4 cycle phase shift with respect to the hf=jℏωc condition for j≥1, and they also suggest a small
(≈ 2%) reduction in the effective mass ratio, m∗/m, with respect
to the standard value for GaAs/AlGaAs devices.Comment: 4 pages, 4 color figure