ABSTRACT
Low temperatures are required to slow down paramagnetic relaxation in order to get sharp EPR spectra. However, when a paramagnet can relax back to the ground state only slowly, then it is easy to saturate the system with microwaves, and this will lead to deformed spectra. In this chapter we consider the two key experimental parameters: power (intensity of the microwaves) and temperature (of the sample) in combination with the key system parameter: the spin. For a given system of spin S at a temperature T there is a single optimal value of P, which must be determined experimentally. The combined set of P, T, and S determines the complexity and the costs of EPR spectroscopy.
