Paramagnetic Resonance Detection along the Polarizing Field Direction

Abstract

Strong rf power, modulated at a low frequency, was applied to a paramagnetic solid (diphenyl pycril hydrazil) in a dc field ${H}_{z}$ of up to 20 gauss. The resulting changes in ${M}_{z}$ at the modulation frequency produced a voltage in a coil oriented in the $z$ direction, to provide a measure of ${M}_{z}$. A sensitive test of the equation of motion of the spin magnetization was achieved by using 19.5-Mc/sec circularly polarized rf of up to 6 gauss in the $x\ensuremath{-}y$ plane, square wave modulated at 280 cps. The observed 280-cps signal was consistent with the Bloch equations, assuming relaxation toward the instantaneous applied magnetic field. As predicted, ${M}_{z}$ was not zero when ${H}_{z}=0$. A Bloch-Seigert effect was also observed.