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High‐Performance Thermomagnetic Generators Based on Heusler Alloy Films
Author(s) -
Gueltig Marcel,
Wendler Frank,
Ossmer Hinnerk,
Ohtsuka Makoto,
Miki Hiroyuki,
Takagi Toshiyuki,
Kohl Manfred
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201601879
Subject(s) - thermomagnetic convection , materials science , alloy , condensed matter physics , ferrimagnetism , ferromagnetism , power density , thermoelectric effect , magnetization , thermoelectric materials , thermodynamics , metallurgy , magnetic field , power (physics) , composite material , thermal conductivity , physics , quantum mechanics
Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm −3 , experimental results have been in the range of µW cm −3 . Challenges are related to the development of materials with bulk‐like single‐crystal properties as well as geometries with large surface‐to‐volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin‐film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm −3 that compares favorably with the best thermoelectric generators. Due to the large temperature‐dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.