Thin Film NiCr-, TiCr- and CuNi-Based Cermets for Low-Temperature Ultra-Low Magnetoresistance Thermometers

Many thermal measurements in high magnetic fields—including heat capacity, thermal conductivity, thermopower, magnetocaloric and thermal Hall effect measurements—require thermometers that are sensitive over a wide temperature range, are low mass, have a rapid thermal response and have a minimal, easily correctable magnetoresistance. We recently reported the development of a new granular-metal oxide ceramic composite (cermet) for this purpose formed by co-sputtering of the metallic alloy nichrome (Ni 0.8 Cr 0.2 ) and the insulator silicon dioxide (SiO 2 ). In this earlier work, we found that co-sputtering of NiCr alloy and SiO 2 in a reactive oxygen and inert argon gas mixture can produce resistive thin-film thermometers sensitive enough to be used in calorimetry and related measurements from room temperature down to below 100 mK in magnetic fields up to at least 35 T. In this work, we present results for thin cermet films grown with Cu 0.55 Ni 0.45 and Ti 0.05 Cr 0.95 . Growth of CuNi-based thin-film cermets generally requires more oxygen in the working gas compared to NiCr and TiCr and yields thermometers that are much less sensitive than comparable NiCr-based thermometers. TiCr-based cermet thin-film thermometers have somewhat higher resistivity for similar sensitivities compared to NiCr-based cermet thin-film thermometers.