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
Data storage using individual molecules
17.12.2018 | Universität Basel
Formed to Meet Customers’ Needs – New Laser Beams for Glass Processing
17.12.2018 | Fraunhofer-Institut für Lasertechnik ILT
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.
Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
17.12.2018 | Physics and Astronomy
17.12.2018 | Architecture and Construction
17.12.2018 | Life Sciences