Magnetocaloric materials heat up when they enter a magnetic field, and cool down again when they leave it. This phenomenon called magnetocaloric effect is known to scientists by more than 100 years and can be exploited to produce quiet, energy efficient, and environmentally friendly heating and cooling devices. But the high cost of materials has however severely hampered its wider application in mass market products.
But now Nikolaos Biniskos from Forschungszentrum Jülich and the French Alternative Energies and Atomic Energy Commission (CEA Grenoble) along with his colleagues have studied a material in which the related inverse magnetocaloric effect occurs at low temperatures: The manganese and silicon alloy cools down when it enters a magnetic field and warms up again after leaving it. Using neutron scattering, the researchers showed that the fluctuation of the electron spins in the material play a role in the formation of the inverse magnetocaloric effect. They are triggered by a magnetic field; entropy increases because of this and gives rise to a cooling effect.
Neutron scattering is especially well suited to determining this kind of spin dynamic. In order to carry out the measurements, instruments at the French institute Laboratoire Léon Brillouin and the European research centre Institut Laue-Langevin were used, where the Jülich Centre for Neutron Science operates a neutron spectrometer. Due to the fact that very good monocrystals are available where spin fluctuations are clearly demonstrable, the Mn5Si3 alloy under investigation proved ideally suitable as a model system for similar materials.
N. Biniskos et al.; Spin fluctuations drive the inverse magnetocaloric effect in Mn5Si3; Phys. Rev. Lett. 120, 257205 – Published 22 June 2018, DOI: 10.1103/PhysRevLett.120.257205