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 divided by 1K te mperature range, and of Manganin wire having a composition of Cu 86%, Ni 2% , Mn 12% (sample 2) in the 0.05 divided by 0.25K 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)T 1.19+/-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 simi lar sensitivity to a small difference in the composition has also been foun d for other Cu alloys.