Magnetocalorics of frustrated Fe2P type-compounds. Two examples: MnRh1-xRuxAs with intricate fundamentals and Mn2-xFexP1-ySiy, for promising cooling applications

Prof. Daniel Fruchart Institut Néel, CNRS, Grenoble France.

By Prof. Daniel Fruchart, Institut Néel, CNRS, Grenoble France.

The increasing demand for refrigeration (industry and domestic applications) concern with up to 20 to 30% of national electric energy, depending on the considered country. The present cooling technology, based on gas compression, is eminently to question since its rather low energy efficiency and COP factor moreover using highly unfriend green-house gas in terms of global warming that are CFC and HCFC. A very interesting alternative was proposed for more than 20 years in terms of magnetic refrigeration, involving both specific magnetic materials and dedicated machines imposing magnetization/demagnetization cycles. Nowadays, magneto-caloric materials and techniques are considered for in many countries in terms of R & D efforts and issues.
The magneto-caloric effect (MCE) consists to transfer as efficiently as possible the change of magnetic enthalpy issued for the magnetization/demagnetization cycle to the atomic lattice of the atoms to develop alternatively heating/cooling of the MC body, thus developing heat/cold sources, parallel.
The several series of promising and presently studied MCE materials can be classified according to specific criteria such as low cost of the elements, processing techniques, corrosion resistance (water-based would be heat transfer fluids), chemical safety, thermal conductivity… and evidently the magneto-caloric performances. The latter aspect is directly related to the density and strength of individual moments shared by the magnetic elements forming the materials.
For the major cooling application domain which is apart room temperature, magnetism of transition elements is the most appropriated since the strength of the exchange couplings reference to rare earth even if the magnetic moments of the former are relatively weaker. Two series of metal type compounds with dense magnetic lattices have merged since exhibiting strong MCE contributions. These are the LaFe13-xSix series (NaZn13 structure type) and the Mn-rich ternary pnictides with the hexagonal Fe2P type of structure.
The presentation will focus on two representative systems of the late series: MnRh1-xRuxAs with intricate fundamentals and Mn2-xFexP1-ySiy effectively promising for application. We have characterized in details such series for many years. We have demonstrated that the Mn sublattice (with a pyramidal non-metal coordination) can develop interesting ferromagnetic ordering, but the resulting fundamental on one side and applied characteristics on the other side straightly depend on the effective polarization of the second metal element (here Fe, Ru, Rh, occupying a tetrahedral site). So the magnetic properties are found very sensitive to the metal and non-metal composition leading to very interesting magnetic phase diagrams versus temperature and pressure, involving or not magneto-elastic couplings.
Systematic structure and magnetic measurements, specific heat, characterization under pressure, Mössbauer spectroscopy data and band structure calculations will be reported illustrating the rich fundamentals as well as promising aspects for applications of those magneto-caloric pnictides.


Daniel FRUCHART, Emeritus CNRS Director, Institut Néel, Grenoble, France. Masters Fund. Maths, Phys. & Crystal., Hab Th. (76).
Research group Intermetallics & Interstitials – Energy Conversion, Institut Néel (82-09).
Co-Found McPhy Energy – Hydrides & Tanks. Found HollyFlow – Materials & Systems for Energy.
Associate Professor, OSU – USA (83)
Head French-Spanish European Lab. MANES (94-02).
European School Committee HERCULES (94-09).
Responsible for > 32 R&D industry, institution and international contracts + 9 EU contracts (CEAM I & II, Nitromag, HYSTORY, NessHy, NanoHy, InsidesPores, StorHy, ATLAS), PICS FRBR (Russia), LIA Xi’an (China)
Supervision > 41 PhD.
Published > 844 papers, mostly in peer reviewed journals. Contribute > 20 books. 14 Patents-CNRS & Industry: RE-Magnets, Na-Elimination from Surgenerator, Arc-melter, Magnetic Nano-arrays, Metal hydrides, Metal hydride tanks, SPD metallurgy. Magnetocalorics
Interests: Magnetic materials: Structure determination, Fund. & appl. magnetic materials (hard, soft, magnetocaloric). Metal-Hydrogen systems: Fund. – structure, physics & appl. properties (storage, HD & HDDR-processes), Tanks. Metallurgy: Severe Plastic Deformation, In up to 7 GPa H2, In magnetic fields (> 10 T). Thin deposits: MOCVD, PAVD. Neutron scatter. & X-ray spectro.: Powder/crystals, magnetism, QNS, SANS, EXAFS, XANES, XMCD
Awards 1-French Div. Mineral Chem. & Metall., 2-Soc. Mater. Spain 3-Bétancourt-Perronet, 4-ADEME Magnetocaloric, 5-French Phys. Soc. – Hydrogen Storage.
Chair Solid StatePhysics, LURE French Synchrotron, 99-03. Magnetic Structure, Inst. Laue-Langevin, 00-02. French Neutron Scattering Division, 98-00. French Neutron Society, 98-01. IAE Expert & IAEA Observer.
Intern. Steering Committees of 5 Conferences – Organised 8 Int. Conferences
Edit. Board of IJHE (98-12) + Ed. Special Issue (15). Scientific Board of MDPI publishers (18)

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