Is the first-order magneto-optical effect really proportional to the magnetization?

摘要

The magnetic and magneto-optical properties of the paramagnetic Nd_3Ga_5O_(12) crystal including the magnetic susceptibility, the magnetization, and circular magnetic birefringence (Faraday rotation) in a large wavelength range under high magnetic field were analyzed within the framework of the one-ion model. H was along the [111] cubic direction in the 4.2-300 K temperature range. A good simulation of all the available experimental results is obtained considering spin-orbit coupling, the crystal field interaction, and the Zeeman effect. The high-order correction of the Zeeman effect plays a very important role. This explains why no saturation of M and of Faraday rotation (FR) happens at very low temperatures even when H is above 30 T.. The main conclusion drawn from our calculation is that the magneto-optical coefficient (Verdet constant divided by magnetic susceptibility) presents a linear variation versus the reciprocal temperature in the 70-300 K range. In other words the first-order magneto-optical effect (FR or circular magnetic birefringence) is not proportional to the magnetization.