Thermal characterisation of a tungsten magnetoresistive heat switch

A magnetoresistive heat switch has been developed to improve the performance of our flight-worthy cryogen-free ADR. We have characterised the switch’s thermal conductivity in the temperature range 0.3-4 K under an applied magnetic field of 1.8 T for two tungsten samples of different purity. The results are discussed relating to the key aspects of semi-classical magnetoresistance theory. We show that crystal purity has a strong effect on switch performance and magnetoresistive effect. Our findings are verified by comparison to results obtained by other authors. The measured switching ratio for our best sample is 1.75 × 10⁴ at 1.5 K and 1.51 × 10⁴ at 4.26 K. The lattice conductivity remains dominated by the electronic conductivity in the investigated range of temperatures under an applied magnetic field of 1.8 T. In order for the lattice conductivity to dominate a purity of >99.999% would be required.