Faraday rotation and magnetic properties of neodynium trifluoride under high magnetic field

Abstract

Faraday rotation (Fr) and magnetization (M) measurements were performed in the trifluoride of neodymium NdF3 in high continuous magnetic field (17 T below 77 K and 30 T above this temperature). The temperature range extends from 15 to 300 K (Fr) and from 1.6 to 300 K (M), respectively; the external field was applied along the (c) direction of the hexagonal structure at 633 nm wavelength. M was found to be linear versus H above 40 K; the magnetic susceptibility (χ) follows a Curie–Weiss law. At low temperature, only the lowest doublet is populated and the saturation of M is observed. Below 30 K, Fr presents a nonlinear field dependence in H higher than 7 T but remains linear in the 30–300 K range. The Verdet constant (V) was then deduced. All the data confirm a complex and unusual temperature variation of the ratio V/χ which cannot be attributed to a strong superexchange coupling between the spins of the Nd3+ ions as previously proposed; they underline a paramagnetic behavior which is influenced by crystal field effects.