Advanced magnetocaloric materials for adiabatic refrigeration – Matadire

We have succeeded in preparation of various samples of Yb3Ga5O12 garnet. High-quality transparent single crystals have been used for basic characterization, including specific heat, magnetization and thermal conductivity measurements as well as neutron experiments. In addition, significant efforts were devoted to growth and optimization of sintering conditions for ceramic samples to be used directly in the ADR coolers. The high-density ceramics (>95%) were obtained with the starting Yb2O3 material provided by « Rhône Poulenc » supplier. It was used to grow a 600 g ADR module. To obtain good thermal conductivity in the ADR cooler we performed detailed investigation of brazing conditions for YbGG ceramics with Ag/Cu/Ti alloys using 2D and 3D brazing techniques. The optimal properties were obtained using 3D brazing with a Cu/Ti alloy. Two patents (France and USA) devoted to brazing of YbGG ceramics were submitted [8].
We have worked out the experimental set up for growing polycrystalline and ceramic samples of GdLiF4. Growth of single crystals is hindered due to traces of humidity in the starting material GdF3 from our supplier.
The magnetocaloric properties were obtained be performing detailed magnetization measurements M(H,T) for various fields and temperatures. The magnetocaloric effect was calculated from the Maxwell relations.
For several astrophysics missions in the selection or design process (SPICA, LiteBIRD, Athena), high sensitivity detectors with the work temperatures from 50 to 100 mK are required. To address this technical challenge a 3-stage ADR with YbGG as the refrigerant material was designed. For the interface temperature 3.5 K, a 24 hrs operation was demonstrated with 25 µW cooling power at 1.2 K, 2 µW at 0.4 K, and 0.5 µW at 50 mK, Similar measurements with an interface temperature of 4.0 K yield 10 µW at 1.3 K, 2 µW at 400 mK and 0.5 µW at 50 mK. Great care has been put into temperature stability measurements including development of a new card ULTM50 produced at SBT, CEA-Grenoble.

Our choice of garnet Yb3Ga5O12 as the principal material for magnetocaloric application proved to be a great success. We demonstrated that it has better magnetocaloric performance in comparison to standard refrigerant materials for temperatures between 350 mK and 2.5 K important for applications. Ceramic samples of Yb3Ga5O12 brazed with Cu/Ti alloys for improved thermal conduction were prepared. We also detailed the magnetocaloric properties of GdLiF4 and demonstrated that its performance extends to significantly lower temperatures in comparison to previously published works. Furthermore, we obtained spectacular magnetic phase diagram of this material including its ordering temperature in zero field Tc = 210 mK and the remarkable 1/3 magnetization plateaus for fields H//c. In the framework of this project, new collaborations have been established with groups of Prof. S. Dutton, University of Cambridge, UK.
In the framework of this collaboration a combined experimental-theoretical study of a new promising magnetocaloric material Ba2GdSbO6 was performed.. Our contribution was theoretical Monte Carlo simulations. Currently, we assess a possibility of growing polycrystalline and single crystals of this new magnetocaloric material in the chemical lab of Partner 1.
Since the start of the project 9 scientific articles were published and 2 patents were produced. Two more publications are in the preparation stage and will be submitted by the end of 2023.

The body of our results have demonstrated a very strong magnetocaloric effect and, consequently, extreme usefulness of the frustrated and dipolar magnetic materials for the ADR applications. Garnet Yb3Ga5O12 has been already employed in the prototype ADR machine. LiGdF4 material, when produced in sufficient quantity will be utilized as well.
A spectacular progress in the thermal heat switche technologies led to a widespread use of a multi stage design of ADR coolers. As a result, a careful selection of the magnetocaloric refrigerant material is requested. This problem can be addressed with further research on frustrated magnets.

Scientific articles:
1.D. A. Paixao Brasiliano, J.-M. Duval, C. Marin, E. Bichaud, J.-P. Brison, M. Zhitomirsky, N. Luchier, “YbGG material for Adiabatic Demagnetization in the 100 mK–3 K range,” Cryogenics 105, 103002 (2020).
2. E. Lhotel, L. Mangin-Thro, E. Ressouche, P. Steffens, E. Bichaud, G. Knebel, J.-P. Brison, C. Marin, S. Raymond, M. E. Zhitomirsky, “Spin dynamics of the quantum dipolar magnet Yb3Ga5O12 in an external field,” Phys. Rev. B 104, 024407 (2021).
3. J.-M. Duval, A. Attard, D.A.P. Brasiliano, IOP Conf. Ser.: Materials Science and Engineering 755, 012122 (2020).
4. R. Schick, T. Ziman, M. E. Zhitomirsky, “Quantum versus thermal fluctuations in the fcc antiferromagnet: Alternative routes to order by disorder,” Phys. Rev. B 102, 220405 (2020).
5. P. Park, K. Park, J. Oh, K. H. Lee, J. C. Leiner, H. Sim, T. Kim, J. Jeong, K. C. Rule, K. Kamazawa, K. Iida, T. G. Perring, H. Woo, S.-W. Cheong, M. E. Zhitomirsky, A. L. Chernyshev, J.-G. Park, “Spin texture induced by non-magnetic doping and spin dynamics in 2D triangular lattice antiferromagnet h-Y(Mn,Al)O3, Nature Communications 12, 2306 (2021).
6. L. Bhaskaran, A. N. Ponomaryov, J. Wosnitza, N. Khan, A. A. Tsirlin, M. E. Zhitomirsky, and S. A. Zvyagin, “Antiferromagnetic resonance in the cubic iridium hexahalides (NH4)2IrCl6 and K2IrCl6,” Phys. Rev. B 104, 184404 (2021).
7. R. Schick, O. Gotze, T. Ziman, R. Zinke, J. Richter, and M. E. Zhitomirsky, “Ground state selection by magnon interactions in an fcc antiferromagnet,” Phys. Rev. B 106, 094431 (2022).
8. E. C. Koskelo, P. Mukherjee, C. Liu, A. C. S. Hamilton, H. S. Ong, M. E. Zhitomirsky, C. Castelnovo, S. E. Dutton, “Comparative study of magnetocaloric properties for Gd3+ compounds with different frustrated lattice geometries,” PRX Energy 2, 033005 (2023).
9. J.-M. Duval, A. Attard, D. A. P. Brasiliano, “Experimental results of ADR cooling tuned for operation at 50 mK or higher temperature,” IOP Conf. Ser.: Materials Science and Engineering 755, 012122 (2020).

Patents:
1. J.-M. Duval, C. Marin et al., Cooling device comprising paramagnetic garnet ceramic, US Patent US2020/0200444Al, June 25, 2020.
2. J.-M. Duval, C. Marin et al., Dispositif De Refroidissement Comprenant Une Ceramique De Grenat Paramagnetique, Institut National De La Propriété Industrielle, No. FR 3 090 830, N° d'enregistrement national 18 73565, date 26.06.2020

The "Matadire" project sets an ambitious goal to modernize and to extend limits of current Adiabatic Demagnetization Refrigeration technologies by thorough search and investigation of new advanced magnetocaloric materials. The importance of Magnetic Refrigeration below 4 Kelvins stems from its independence of scarce helium isotopes, its simplicity and low operation costs as well as its growing importance for emerging quantum technologies and space applications.
Guided by simple and transparent physical ideas based on modern developments in the field of magnetism, we suggest three prospective families of magnetocaloric materials: Yb-garnets and Yb-pyrochlores, Yb-intermetallics, and dipolar magnets. Some of them are partly known in applied research but the others, like Yb-garnet and Yb-pyrochlore, are completely new. Our preliminary results show an immediate advantage of the Yb-garnet for Magnetic refrigeration over standard refrigerant materials.
We will grow single crystals, polycrystalline samples and ceramics of the candidate materials and perform their investigation using the best experimental techniques developed for fundamental studies in condensed matter physics that are usually unavailable in applied research laboratories. Material selection, crystal growth, and the experimental investigations of the magnetocaloric effect will be accompanied and guided by extensive theoretical work based on Monte Carlo simulations of pure and disordered magnetic materials. The selected materials will be then implemented in the prototype Magnetic Refrigerators that will provide direct comparison of the efficiency of new materials with respect to standard refrigerants.
Studying within the same project three different families of materials with diverse properties: ferro- and antiferromagnets, insulators and metals, we adopt basically a “no fail approach” - we are convinced to find among them the new refrigerants that will outperform the currently used systems at least for certain temperature intervals.
To achieve our challenging goals we gathered 3 teams from different Labs sharing complementary expertise and covering all needs for the Project's success: 1) strong skills in sample growing, 2) instrumentation for measurements at low- and ultra low-temperatures, 3) theoretical expertise in magnetocaloric effect and modeling of magnetic systems and 4) major experience in constructing Adiabatic Demagnetization Refrigerators for space and ground applications. The combination of top teams from basic research and applied sciences is really unique and provides a rare opportunity to make important technological breakthrough.