Electron-Paramagnetic-Resonance Spectrum at Low Temperatures

Abstract

The EPR spectrum at low temperatures is investigated for weakly exchange-coupled spins in the uniaxial crystalline field with the aid of Kubo-Tomita’s method. A method is presented to decompose the unperturbed evolution in the time-correlation function into Fourier components and express the function in terms of static spin-correlation functions. The line shape for S=1 is obtained explicitly using some approximations and the effects of the exchange interaction to the peak position and half-valued width of each main line are investigated at low temperatures. The results are compared numerically with previous results. It is shown that the contribution of the second-order shift to the line shift is significant for each line and variation of the peak position of the strong line with temperature is sensitivity influenced by the magnitude of the exchange constant and the resonance frequency applied. The effect of a satellite line of the strong line to the spectrum of the weak line is also discussed.