A high field Faraday magnetometer for measurements under high pressure (abstract)

Abstract

Commercially supplied SQUID magnetometers which provide the best sensitivity (10−8 emu) are becoming more popular for routine magnetic property measurements. However, these magnetometers generally provide a very small usable sample space (9 mm) and a maximum field limited to 5.5 T. The sensitivity of SQUID magnetometers drops with increasing magnetic fields strengths and becomes comparable to or lesser than the sensitivity of Faraday magnetometers at a field of 5.5 T (5×10−5 emu). Therefore, Faraday magnetometers are a better choice, if a high sensitivity in high magnetic fields is required and/or a large sample space is needed, for example, to accommodate a pressure clamp for high pressure measurements. We have constructed a Faraday magnetometer which facilitates the measurements under high pressure conditions (up to 20 kbars in Cu–Be clamps) and in fields up to 13 T in a 24 mm warm bore (1.3–300 K) and 45 mm cold bore. To accommodate the weight of the pressure clamp, the magnetometer is equipped with a microbalance of extended weighing capacity (100 g) with a sensitivity of 10−6 g. Its superconducting magnet was specially designed to have a gradient such that the product H dH/dz remains nearly constant over a cylindrical sample volume of 20 mm×50 mm, which is the typical size of our pressure clamps. The details of pressure clamps will also be discussed.