International University of Rabat, Morocco
By Prof. Mohamed Balli, International University of Rabat, Morocco.
Over the last decades, the growing concerns about environment and energy efficiency issues have motivated worldwide research works that aim to drastically reduce the energy consumption, improve the efficiency of existing technologies and eliminate hazardous gases emission while insuring better energy security. In this context, a large-scale utilization of hydrogen as a fuel and energy carrier will result in major economic and ecological gains. However, the search for simple, cheaper, and efficient techniques to safely store hydrogen is crucial prior to the broad use of this promising source of energy. Currently, the hydrogen is usually stored via a liquefaction process by decreasing its temperature and/or by subjecting it to high pressures. Unfortunately, the production of liquid-hydrogen requires high energy consumption in addition to safety risks arising from high pressures and storage cryogenic temperature that is about -250 °C. In this context, a magnetic cooling technique which is based on the magnetocaloric effect (MCE) would be a serious alternative since the liquefaction process is achieved by simply magnetizing and demagnetizing some magnetic materials during an active magnetic refrigeration (AMR) thermodynamic cycle [1]. Additionally, this promising technology enables us to fully suppress the hazardous fluorinated refrigerants which are widely used in standard systems while presenting higher thermodynamic efficiency. Recently, an innovative hydrogen liquefier based on the AMR technique has been unveiled by a Japanese team [2, 3]. In the developed device, the liquefaction process is carried out by employing the magnetocaloric garnet Dy2.4Gd0.6Al5O12 as refrigerant, decreasing accordingly the hydrogen temperature down to 20 K. Unfortunately, this sort of materials exhibits a large specific heat which negatively impacts their adiabatic temperature change that reaches only 1 to 2 K in the magnetic field variation of 1 T [2, 3]. Hence, the search for advanced magnetocaloric materials with giant (outstanding) MCE in the cryogenic temperature range below 50 K is a key parameter for the development of hydrogen magnetic liquefiers. In this way, RMnO3 and RMn2O5 (R = rare earth) multiferroics [4-6] are among the most interesting materials for application in magnetic refrigeration at low temperatures. In fact, the presence of several exchange interactions involving Mn and R ions results in a wide variety of electrical and magnetic transitions associated with giant MCEs below 50 K that is usually obtained by varying external magnetic fields. More importantly, the strong interaction between R
In this presentation, I will first introduce magnetocaloric materials and magnetic refrigeration. The driving mechanisms behind the magnetism and the magnetocaloric effect in RMnO3 and RMn2O5 will be explained. Recent developments in relation to their magnetocaloric properties including anisotropic MCEs will be reviewed. Their implementation as active materials in cryo-magnetocaloric liquefiers will be discussed.
References
[1] M. Balli, S. Jandl, P. Fournier, A. Kedous-Lebouc, Appl. Phys. Rev. 4, 021305 (2017).
[2] K. Matsumoto, T. Kondo, S. Yoshioka, K. Kamiya and T. Numazawa, J. Phys.: Conference Series, 150, 012028 (2009).
[3] T. Numazawa, K. Kamiya, T. Utaki, K. Matsumoto, Cryogenics. 62, 185 (2014).
[4] M. Balli, B. Roberge, P. Fournier and S. Jandl, Crystals 7, 44 (2017).
[5] M. Balli, S. Jandl, P. Fournier, M. M. Gospodinov, Appl. Phys. Lett. 104, 232402 (2014).
[6] M. Balli, S. Jandl, P. Fournier, M. M. Gospodinov, Appl. Phys. Lett. 108, 102401 (2016).
Biography
Pr. Dr. 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.