Current Trends in Magnetocaloric Materials: An FMD Symposium in Honor of Ekkes Brueck: Strain Enhanced Magnetocaloric, Barocaloric Materials, and Thermomagnetic Generators
Sponsored by: TMS Functional Materials Division
Program Organizers: Victorino Franco, Universidad de Sevilla; Frank Johnson, Niron Magnetics, Inc.
Tuesday 8:30 AM
February 25, 2020
Room: Marina Ballroom F
Location: Marriott Marquis Hotel
Session Chair: Victorino Franco, Universidad de Sevilla
8:30 AM Invited
Tuning Magnetocaloric Materials with Stress: Xavier Moya1; Enric Stern-Taulats1; 1University of Cambridge
Mechanical stress can modify the magnitude of a magnetocaloric effect, the operating temperature, and the hysteretic losses. Mechanical stress can also create new phase transitions, permitting large magnetocaloric effects to be explored in an expanded range of materials, and even be used to drive mechanocaloric effects in magnetocaloric materials. Here I will present recent advances on magnetocaloric materials tuned with and driven by stress.
9:00 AM Invited
Under Pressure: Probing Magneto-structural Coupling in MCE Materials: Luana Caron1; Sanjay Singh2; Ekkes Brueck3; Claudia Felser4; 1Bielefeld University; 2Indian Institute of Technology (Banaras Hindu University), Varanasi; 3TUDelft; 4Max Planck Institute for Chemical Physics of Solids
Applications of the magnetocaloric effect, specially heat pumps, rely on large reversible adiabatic temperature and entropy changes observed around first order phase transitions. At the core of the large effect is the strong magneto-structural coupling responsible for first order phase transitions where both the magnetic and crystal lattices contribute significantly to the MCE. Thus, understanding the magneto-structural coupling in magnetocaloric materials is paramount for the development of novel, better materials for applications. In this work the effect of hydrostatic pressure on the magneto-structural coupling in MnCoGe, (Fe,Mn)2(P,Si) and Ni2Mn1.4In0.6 magnetocaloric materials is explored. The effect of hydrostatic pressure on the magneto-structural coupling sheds light on the origin of irreversibilities due thermal hysteresis in these materials, pointing a way to improve their properties and therefore make them more efficient for applications.
9:30 AM Invited
Giant Barocaloric Effect at the Spin Crossover Transition of a Molecular Crystal: Steven Vallone1; Anthony Tantillo1; António dos Santos2; Jamie Molaison2; Rafal Kulmaczewski3; Antonin Chapoy4; Pezhman Ahmadi4; Malcolm Halcrow3; Karl Sandeman1; 1The City University of New York; 2Oak Ridge National Laboratory; 3University of Leeds; 4Heriot-Watt University
Spin crossover occurs in compounds where the crystal field splitting of d-orbitals associated with a magnetic moment is of the order of kBT. As a result, a change of state from low spin (LS) to high spin (HS) can occur at the so-called spin crossover temperature, TSCO. Crucially for caloric applications, the change of state from LS to HS can be either continuous or first order, and it can occur at temperatures up to and beyond room temperature. This makes SCO transitions of interest for caloric cooling applications. Since SCO compounds are paramagnets or diamagnets, the largest caloric effects will be barocaloric rather than magnetocaloric.In this presentation, we provide the first direct experimental demonstration of a giant, low pressure barocaloric effect (BCE) and outline future research directions for the development and optimization of the BCE associated with spin crossover.
10:00 AM Break
10:20 AM Invited
Energy Harvesting Using Thermomagnetic Generators with Magnetocaloric Materials: Anja Waske1; Dzekan2; Bruno Neumann2; Dietmar Berger2; Kai Sellschopp3; Alexander Stork2; Kornelius Nielsch2; Sebastian Fähler2; 1Bundesanstalt für Materialforschung; 2IFW Dresden; 3Technische Universität Hamburg
To date, there are only very few technologies available for the conversion of low temperature waste heat to electricity. More than a century ago, thermomagnetic generators were proposed, which are based on a change of magnetization with temperature, switching a magnetic flux, which according to Faraday’s law induces a voltage. In this talk, we first describe the principle of thermomagnetic generators. Then we focus on the impact of topology of the magnetic circuit within thermomagnetic generators. We demonstrate that the key operational parameters strongly depend on the genus, i.e. the number of holes within the magnetic circuit. A pretzel-like topology of the magnetic circuit with genus =3 improves the performance of thermomagnetic generators by orders of magnitude. We will show that this technique is on its way to becoming competitive with thermoelectrics for energy harvesting near room temperature.
10:50 AM Invited
Materials for Thermomagnetic Harvesting of Low Temperature Waste Heat: Daniel Dzekan1; Anja Waske2; Kornelius Nielsch1; Sebastian Fähler1; 1Leibniz IFW Dresden; 2Bundesanstalt für Materialforschung und –prüfung (BAM)
Thermomagnetic materials are a new type of magnetic energy materials, which enable the conversion of low temperature waste heat to electricity by three routes: Thermomagnetic motors, generators and microsystems. Taking our recent work on thermomagnetic generators [1] as a starting point, in this talk we analyse the material requirements for a more energy and economic efficient conversion. We will describe the influence of magnetisation change and heat capacity on thermodynamic efficiency, as well as the consequences of thermal conductivity on power density. Our analysis will allow selecting the best thermomagnetic materials in Ashby plots and illustrate the substantial different properties compared to magnetocaloric materials. Supported by DFG, project FA 453/14)[1] A. Waske, D. Dzekan, K. Sellschopp, D. Berger, A. Stork, K. Nielsch, S. Fähler, Energy harvesting near room temperature using a thermomagnetic generator with a pretzel-like magnetic flux topology, Nature Energy 4 (2019) 68, https://rdcu.be/be4fv
11:20 AM Invited
Rare-earth-free Permanent Magnets: The Past and Future: J. Ping Liu1; 1University of Texas at Arlington
Permanent magnets are essential components in everyday technology and applied in many devices including energy conversion and transportation devices. Since the discovery of rare-earth-based permanent magnets in the 1960s, we have seen great improvement in magnets performance and incredible growth in the production. However, permanent magnets have not been developed in a diversified way. Over past decades, rare-earth-free permanent magnets have played an important role in applications and recent research has shown further potential for development of novel rare-earth-free magnets. In this presentation we will reviews the past and recent advances in rare-earth-free permanent magnets based on 3d transition metals and their alloys with large coercivity. Nanostructured permanent magnetic materials, including exchange-coupled nanocomposite permanent magnets and ferromagnetic nanowires, which are considered as the new types of high-strength permanent magnets, are also discussed.
11:50 AM Concluding Comments