Published measurements of Faraday rotation in a variety of materials in pulsed magnetic fields show a time-dependent or hysteresis effect in which the angle of rotation lags the magnetic field as a function of time. We show that this effect is an artifact introduced by using a passive resistance-capacitance circuit to integrate the induced electromotive force (EMF) from a pickup coil to obtain the magnetic field. By numerically integrating the sampled-induced EMF signal, the effect vanishes. However, we propose an experimental situation where such a time lag should appear, allowing measurement of the spin-lattice relaxation time of the ion responsible for the Faraday rotation.
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