Observation of Electron Paramagnetic Resonances at Multiples of the "Classical" Resonance Magnetic Field

Observation of electron paramagnetic resonance signals at multiples (up to 7) of the conventional magnetic resonance field are reported in the case of the system GaP: Cr⁺ at low temperatures. These signals are shown to be due to multiphoton transitions. The physical reason for the observation of these resonances is a long relaxation time consistent with the physical nature of this paramagnetic center.