Current Trends in Magnetocaloric Materials: An FMD Symposium in Honor of Ekkes Brueck: Characterization of Structure and Magnetic Properties of Magnetocaloric Materials
Sponsored by: TMS Functional Materials Division
Program Organizers: Victorino Franco, Universidad de Sevilla; Frank Johnson, Niron Magnetics, Inc.

Monday 8:00 AM
February 24, 2020
Room: Marina Ballroom F
Location: Marriott Marquis Hotel

Session Chair: Durga Paudyal, Ames Laboratory


8:00 AM Introductory Comments

8:05 AM  Invited
Fe2P an Intriguing Binary Alloy: Ekkes Brueck1; 1TU Delft
     The Fe2P intermetallic compound, is a prototypical example of a first order ferromagnetic phase transition, known since the 1980s to exhibit a sharp, but weak, FOMT at 216 K (-57°C)[1]. In this hexagonal system, the Fe atoms occupy two inequivalent atomic positions, referred to as 3f (in a tetrahedral environment of non-metallic atoms) and 3g (in a pyramidal environment). Also for P we find two distinct lattice sites 1a and 2b. One intriguing aspect is the strong reduction (partial quenching) in the magnetic moments of the iron atoms on the 3f sites when TC is crossed from the ferromagnetic to the paramagnetic state, whereas there is only a limited decrease on the 3g site. This observation has led to a cooperative description of the FOMT, linking the loss of long-range magnetic order at TC with the loss of local moments on the 3f site[2]. Replacing Fe and or P by other elements leads to a rich variety of phenomena. [1]. In O. Beckman et al., Specific Heat of the Ferromagnet Fe2P. Physica Scripta 25 (1982) 679-681; [2]. H. Yamada and K. Terao, Phase Transitions, 2002, Vol. 75, No. 1–2, pp. 231–242.

8:35 AM  Invited
CaloriSMART – A New Tool for Rapid Experimental Evaluation of Active Magnetic Regenerator Materials: Lucas Griffth1; Agata Czernuszewicz1; Julie Slaughter1; Vitalij Pecharsky1; 1Ames Laboratory
    New magnetocaloric materials are commonly characterized only with respect to their basic magnetic properties. This makes it difficult to predict materials’ performance in a magnetocaloric heat pump because heat transfer models require other parameters that are not routinely measured and may change after processing into an active magnetic regenerator. The key features of CaloriSMART include i) small (approximately 5 ml) volume of regenerator; ii) direct comparison of regenerator performance at two different maximum magnetic field strengths; iii) broad range of operating frequencies, fluid flows, and fluid flow profiles; and iv) rapid, fully automated testing, with most materials and regenerators evaluated in as little as two days. This research is supported by the Office of Energy Efficiency and Renewable Energy of the U.S. Department of Energy (DOE) through the Advanced Manufacturing and Building Technologies Offices. Ames Laboratory is operated for the U.S. DOE by Iowa State University under Contract No. DE-AC02-07CH11358.

9:05 AM  Invited
Quantitative Identification of First-order Phase Transitions Using Magnetocaloric Studies: Jia Yan Law1; 1Sevilla University
     The usual techniques to determine the order of phase transitions depend on interpretations based on qualitative data features, thus jeopardized by misinterpretations or extensive calculations. In this talk, we show that using the field dependence of isothermal entropy change (magnetocaloric effect), the order of the phase transition can be quantitatively determined: an exponent n larger than 2 at the transition constitutes the fingerprint of first-order thermomagnetic phase transition [1]. This newly proposed alternative to identify the order of thermomagnetic phase transitions will be applied to various series of magnetic materials, including alloys, oxides and multiphase composites. This technique could outdo the accuracy of the typical methods used for identifying the order of magnetic phase transitions, especially for compositions very near to the critical point of second-order phase transition. [1] J. Y. Law, et al., Nature Communications, 9, 2680 (2018).

9:35 AM Break

9:55 AM  Invited
Synchrotron X-ray Studies on Magnetocaloric Materials: Niels Van Dijk1; 1Delft University of Technology
    In the last two decades growing research efforts have focused on the development of magnetocaloric materials. Materials that show a sizeable magnetocaloric effect near room temperature are excellently suited for magnetic cooling and energy conversion applications. For systems that show a ferromagnetic transition that is accompanied by latent heat a giant magnetocaloric effect is found. In the (Fe,Mn)2(P,X) compounds (X = As, Ge, Si) attention has focused on optimizing the magnetocaloric materials properties and on the fundamental understanding of the origin of the unusual magnetoelastic transition. Compositional tuning allows for a detailed control of the operating temperatures and performance characteristics. Synchrotron X-ray studies, combined with density functional theory calculations, provide a detailed insight in the nature of the giant magnetocaloric effect. They reveal information on subtle changes in the electronic charge redistribution, the element-specific magnetic moments and the phonon density of states across the ferromagnetic transition.

10:25 AM  Invited
Structure, Magnetisim and Spin Dynamics of Magnetocaloric Mn5-xFexSi3 Compounds: Karen Friese1; Nikolaos Biniskos1; Nour Maraytta1; Paul Hering1; Yuri Skourski2; Andrzej Grzechnik3; Stephane Raymond4; Joerg Voigt1; Thomas Brueckel1; Karin Schmalzl1; 1Research Centre Jülich GmbH; 2Helmholtz Zentrum Dresden Rossendorf; 3RWTH Aachen University; 4Universite des Alpes
     We extensively studied the structure, magnetism, magnetocaloric effect and spin dynamics in the Mn5-xFexSi3 series of compounds [1-3]. While the magnetocaloric effect is moderate for these compounds, they are composed of abundant and non-toxic elements and can be grown as large single crystals. This allowed us to perform direction-dependent magnetization measurements in static and pulsed magnetic fields and to charatcerize the crystal and magnetic structures using single crystal x-ray and neutron diffraction experiments. In addition, inelastic neutron scattering studies of the spin and lattice dynamics on these materials give insight into the microscopic mechanism of the MCE. [1] P. Hering et al; Chemistry of Materials 27 (2015), 7128 [2] N. Biniskos et al; Physical Review B 96 (2017), 104407[3] N. Maraytta et.al; J. Alloys Compds. 805 (2019), 1161