Regensburg 2019 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 63: Poster Session: Cryogenic Particle Detectors and Cryotechnique
TT 63.10: Poster
Thursday, April 4, 2019, 15:00–18:30, Poster D
Specific Heat of Dilute Alloys of Holmium in Noble Metals at Low Temperatures — •Matthew Herbst, Clemens Velte, Andreas Reifenberger, Federica Mantegazzini, Andreas Fleischmann, Loredana Gastaldo, Andreas Reiser, Sebastian Kempf, and Christian Enss — Kirchhoff-Institute for Physics, Heidelberg University, D-69120 Heidelberg
We investigate dilute alloys of holmium in gold and silver in order to determine the impact of their specific heat on the performance of the microcalorimeters in the neutrino mass experiment ECHo. In particular, we focus on alloys with atomic concentrations of xHo=10−2 – 10−4 at temperatures between 10 mK and 800 mK. Due to the large total angular momentum J=8 and nuclear spin I=7/2 of holmium, the specific heat of Ag:Ho and Au:Ho depends on the detailed interplay of various interactions. This makes it unfeasible to accurately determine the specific heat of these materials numerically. Instead, we acquire the desired information through experiment, using three different experimental set-ups. The results from measurements on five holmium alloys show that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at T≈250 mK, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. We find no significant difference between Ag:Ho and Au:Ho, and conclude that alloys with xHo≈1% are suitable for the ECHo project at T≤30 mK.