New quantum material significantly improves adiabatic demagnetization cooling
To reach temperatures closely above absolute zero at −273.16 °C the demagnetization of magnetic materials under adiabatic, i.e., thermally insulated, conditions is utilized. Up to now, diluted magnetic salts have been used for this purpose. Researchers from Augsburg, Göttingen, Kyoto and Iowa State University report in „Science Advances“ on the discovery of a new metallic compound with super-heavy electrons, whose cooling efficiency significantly beats that of currently used paramagnetic salts.
Fundamental research often requires very low temperatures, e.g. to investigate novel quantum effects in matter or to operate highly sensitive particle detectors. Usually the very rare 3-He isotope is utilized for cooling. It exhibits the lowest boiling point of matter but its price is extraordinary high. Over the last decade it increased more than tenfold.
Established: adiabatic demagnetization of paramagnetic salts
The adiabatic demagnetization method is a well-priced and uncomplicated alternative for using 3-He gas. It utilizes magnetic salts whose moments interact so weakly without magnetic field, that they are randomly oriented and order themselves only at very low temperatures. In a moderately large magnetic field the moments are aligned already at enhanced temperature. The entropy is a measure of the degree of disorder or misalignment of the moments. For cooling, the moments are therefore first aligned in a field, to reduce their entropy. Subsequently, the magnetic field is decreased to zero under adiabatic conditions that is without heat exchange to the environment. Because entropy remains constant during this processes, the material can only keep its low entropy if it cools down to very low temperatures.
Significant improvement of efficiency
Commercial adiabatic demagnetization uses paramagnetic salts. However, their thermal conductivity is so bad, that a network of metal wires has to be introduced to them, which significantly reduces the efficiency of the cooling substance per volume. Consequently, the physicists from Augsburg University together with collaborators from Göttingen University, Kyoto University and the Iowa State University intended to develop an alternative cooling substance with improved thermal conductivity. The new synthesized compound (Yb1-xScx)Co2Zn20 has the potential to significantly improve adiabatic demagnetization cooling.
Upon cooling a metal with magnetic moments, typically either ordering of the moments occurs or the moments are getting invalid due to their screening by the conduction electrons. In both cases the entropy is strongly reduced already at elevated temperatures preventing adiabatic demagnetization cooling to very low temperatures. “Aim of our research has been to avoid both effects simultaneously. If successful, it would enable effective cooling by a magnetic metal”, says Prof. Dr. Philipp Gegenwart, leader of the project at Augsburg University.
Formation of super-heavy electrons at low temperatures
The newly discovered (Yb1-xScx)Co2Zn20 fulfills all requirements for the desired properties. As shown in the attached sketch of its structure (inset), the magnetic Yb moments are surrounded by cages from Zn atoms. This structural arrangement is crucial. On the one hand, it hinders the screening of the Yb moments by the Co conduction electrons, on the other hand it also impedes the formation of long-range order. Consequently, the weak interaction of Yb moments and their environment leads to the formation of super-heavy electrons at low temperatures. A small dilution of the Yb atoms by non-magnetic Sc tunes the onset of magnetic order to exact zero temperature. Such a “quantum critical point” in principle allows for cooling down to absolute zero.
Even below 0.03 K
The data published in „Science Advances“ indicate that the new compound, developed by Gegenwart and his international team, cools very strongly during adiabatic demagnetization – even below the lowest measureable temperature 0.03 K of the used setup. Cooling efficiency and thermal conductivity of the new material are significantly better compared to that of magnetic salts evidencing its suitability for improving current low-temperature cooling devices.
Y. Tokiwa, B. Piening, H. S. Jeevan, S.L. Bud’ko. P. C. Canfield, P. Gegenwart, Super-heavy electron material as metallic refrigerant for adiabatic demagnetization cooling. Sci. Adv. 2, e1600835 (2016).
Prof. Dr. Philipp Gegenwart
Lehrstuhl für Experimentalphysik VI/EKM
Institut für Physik / Zentrum für Elektronische Korrelationen und Magnetismus
Klaus P. Prem | idw - Informationsdienst Wissenschaft
SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute
New survey hints at exotic origin for the Cold Spot
26.04.2017 | Royal Astronomical Society
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
26.04.2017 | Materials Sciences
26.04.2017 | Agricultural and Forestry Science
26.04.2017 | Physics and Astronomy