Thermal conductivity of Manganin below 1 K

We carried out thermal conductivity measurements of Manganin wire having a composition of Cu 84%, Ni 4%, Mn 12% (sample 1) in the 0.1/1 K temperature range, and of Manganin wire having a composition of Cu 86%, Ni 2%, Mn 12% (sample 2) in the 0.05/0.25 K range. The measurements were performed in a low-power dilution refrigerator. For sample 1, the fit on the data gives a dependence on T: k = (0.79 ± 0.01)T1.22±0.02 mW/cmK; for sample 2, the fit leads to k = (0.95 ± 0.04)T1.19±0.02 mW/cmK. The difference in thermal conductivity in the overlapping temperature range depends on the different ratio of the Cu/Ni content of the samples. A similar sensitivity to a small difference in the composition has also been found for other Cu alloys