VIBRATING-WIRE VISCOMETERS IN HIGH MAGNETIC-FIELDS

We report an investigation of the intrinsic properties of vibrating wi res made of different materials at low temperatures (approximate to 10 mK < T < 400 mK) and at high magnetic fields (B less than or equal to 11.5 T). The aim of this study was to find a material with sufficient ly low intrinsic damping even in the highest fields to allow accurate viscometry in highly diluted spin-polarized He-3-He-4 solutions. A thr ough theoretical treatment of the behavior of vibrating wires (with a high quality factor) in high magnetic fields is presented. Experimenta l data obtained for NbTi, Ta, W, Ag, manganin and PtW are analyzed wit hin the framework of this theoretical description. Measurements of the field- and temperature dependence of the shift of the resonance frequ ency and of the internal friction of the vibrating wires clearly indic ate that PtW is the most suitable amongst the materials investigated f or vibrating wire viscometry in quantum liquids in high magnetic field s.