International University of Rabat, Morocco
By Prof. Mohamed Balli, AMEEC Team, LERMA, College of Engineering and Architecture, International University of Rabat, Morocco.
Nowadays, the scarcity of energy resources combined with ecological issues caused by fossil fuels have motivated worldwide research activities regarding the development of more efficient and ecofriendly technologies, including cooling systems. In this context, magnetic cooling (heating) which is based on the magnetocaloric effect (MCE) is a promising alternative to the standard compression-relaxation refrigerators, owing to its potential high efficiency and “green” characteristics [1, 2]. In fact, the implementation of magnetocaloric refrigeration would enable us to phase out the hazardous-fluorinated fluids that are widely used in conventional technologies while reaching more than 60 % of Carnot efficiency [2]. It is worthy to underline that in magnetic cooling systems, the higher the generated MCE is, the more powerful system may be. So, the development of magnetocaloric materials with outstanding magnetocaloric properties is crucial for the commercialization of this emerging technology. In this way, several promising magnetic refrigerants have been reported over the last two decades as serious alternatives to the expensive and the chemically instable gadolinium metal (Gd). This includes oxides and intermetallic compounds such as MnFe (P, Ge, Si), La (Fe, Co, Mn)13-xSix(H, C)y and La2/3(Ca, Sr)1\3MnO3 [1]. However, although worldwide investigations have been conducted with the aim to enhancing their magnetocaloric performance, the reported MCE particularly in terms of adiabatic temperature change (ΔTad) remained lower or comparable to that of Gd. Thus, it is necessary to boost the research on magnetocaloric materials by adopting new approaches and creating new designs.
Keeping this in mind, the nanoscience approach would open new avenues for the design of new powerful magnetocaloric materials with unusual properties [3-5]. On the other hand, the investigation of magnetic materials by using nanostructures, low volume samples and heterostructures will help understanding the coupling phenomena as well as the driving mechanisms that control the MCE. For such investigations, the AMO3-type perovskite oxides (A = Lanthanide, M = Metal) are excellent candidates because of their fascinating physical properties induced by the strong coupling between the structural and electronic ordering parameters [6, 7]. Some of them, exhibit several degrees of freedom such as magnetization, electrical polarization, atomic lattice, charge, and orbital ordering parameters. The competition as well as the cooperation between the latter would favor the appearance of instable states associated with large caloric effects. In addition, the electronic, magnetic and magnetocaloric properties in these materials are usually controlled by the super-exchange interactions involving the M-O-M bond that can be markedly modified under doping or strain effects [6, 7].
In this talk, I will mainly focus on the magnetic and magnetocaloric properties of RVO3 (R = rare earth) perovskite orthovanadates [5, 9] and La2NiMnO6-based double perovskites [4, 8] that could be used as active refrigerants in low and room-temperature magnetic cooling applications, respectively. Particularly, I will show how the thin films approach can be used to enhance the magnetocaloric performance of these compounds.
References
[1] M. Balli, S. Jandl, P. Fournier, A. Kedous-Lebouc, Appl. Phys. Rev. 4, 021305 (2017).
[2] C. Zimm, A. Jastrab, A. Sternberg, V.K. Pecharsky, K. Gschneidner Jr., M. Osborne, I. Anderson, Adv. Cryog. Eng. 43, 1759 (1998).
[3] Casey W. Miller, Dustin D. Belyea and Brian J. Kirby, J. Vac. Sci. Technol. A 32, 040802 (2014)
[4] D. Matte, M. de Lafontaine, A. Ouellet, M. Balli, and P. Fournier, Phys. Rev. Applied 9, 054042 (2018).
[5] Bouhani et al., Appl. Phys. Lett. 117, 072402 (2020).
[6] J. B. Goodenough, A. Wold, R. J. Arnott, and N. Menyuk, Phys. Rev. 124, 373 (1961).
[7] J. B. Goodenough, Magnetism and the Chemical Bond (Inter-Science, New York, 1976).
[8] M. Balli, P. Fournier, S. Jandl, and M. M. Gospodinov, J. Appl. Phys. 115, 173904 (2014).
[9] M. Balli, B. Roberge, S. Jandl, P. Fournier, T. T. M. Palstra, and A. A. Nugroho, J. Appl. Phys. 118, 073903 (2015).
Biography
Pr. Mohamed Balli is aiming to understand how to particularly make magnetic materials useful in our daily life such as clean and efficient refrigeration, gas storage, cancer treatment and much more. M. Balli received his Master degree in Mechanics of Materials from Montpellier II University (France), a second Master degree in Magnetism from Joseph Fourier University, Grenoble 1 (France) and, a PhD degree in physics of materials specializing in magnetocaloric materials, from Joseph Fourier University, prepared at Néel Institute (CNRS). Between 2008 and 2012, he was Enseignant-Chercheur at the University of Applied Sciences of Western Switzerland, before joining the University of Sherbrooke, Canada, where he worked as Senior Researcher at the Physics Department and Quantum Institute. Since January 2019, he is Associate Professor of Physics at the International University of Rabat. He is a member of the Working Party on Magnetic Refrigeration, International Institute of Refrigeration (IIR, Paris). He is also a guest editor and editorial board member of the Journal Crystals (IF:2.14). He has published on magnetic materials, multiferroics and systems more than 90 peer-reviewed articles in reputed journals (including roughly 50 papers as the first author). He particularly discovered a large thermal effect in HoMn2O5 crystals that can be obtained simply by spinning them in a constant magnetic field and accordingly proposed an innovative design for the liquefaction of helium and hydrogen. He also questioned the discovery of the so-called colossal magnetocaloric effect (MCE) in Mn1-xFexAs compounds (reported in nature) and concluded that the reported MCE values are spurious due to the inadequate use of Maxwell equation. His patent on LaFeSi-based materials is currently a subject of commercialization and industrialization by ArcelorMittal and Erasteel companies. On the other hand, his research activities on caloric devices have led in 2012 to the creation of Clean Cooling Systems (CCS), a Swiss company specializing in the development of green technologies for refrigeration applications and, magnetic field sources. His research work on magnetocalorics has received numerous awards including, Rising Star Researcher award given by the Research Fund: Nature and Technology, Canada (2014) and the “Research and Innovation Prize 2015” from Sherbrooke University. M. Balli has an H-index of 25.