Abstract

A theoretial treatment is provided for the calculation of EPR (electron paramagnetic resonance) lineshape as affected by interactions with a cluster of paramagnetic ions in the sample. The internal fields seen by the various paramagnetic ions due to interactions with clusters of paramagnetic ions in their vicinity, as well as the resulting lineshapes, are different at high magnetic fields required in high-frequency EPR. The resulting EPR signals for the various ions are characterized by different g-shifts and lineshapes, so that the overall EPR lineshape, which is an overlap of these, becomes distorted, or even split, from that observed at lower frequencies. The observed EPR lineshapes in MnSO4.H2O powder and K3CrO8 single-crystal samples have been simulated here to show that in these samples, concentrated in paramagnetic spins, the position and lineshapes of EPR signals are significantly modified in high-field high-frequency (HFHF) EPR involving very high magnetic fields. These simulations show that it is important to take into account the effect of enhanced internal fields and modifications of HFHF EPR lineshapes to provide a more accurate interpretation of the observed EPR signals.