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| Hauptseite > Publikationsdatenbank > Elucidating the Mechanism of the Magnetocaloric Effect in Compounds of the Series Mn5-xFexSi3 |
| Hauptseite > Publikationsdatenbank > Elucidating the Mechanism of the Magnetocaloric Effect in Compounds of the Series Mn5-xFexSi3 |
| Conference Presentation (Invited) | FZJ-2023-01533 |
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2023
Abstract: Domestic and industrial refrigeration applications contribute a substantial part to mankind's energy consumption. New technologies based on solid state caloric effects promise considerable efficiency gains as compared to today’s vapor compression technology. In caloric materials, applied fields (e.g. magnetic, electric, pressure, strain) lead to changes in entropy and in the adiabatic temperature. The observed caloric effects form the basis of the caloric refrigeration cycles. Within our research we aim at a better understanding of the relation between the structure and the dynamics of the materials to guide a sustainable material design.We focused our research on the magnetocaloric effect in the family of compounds Mn5-xFexSi3. Within the series the magnetocaloric behavior changes from an inverse MCE below 100 K for the end member Mn5Si3 (x=0) to a moderately high direct MCE close to room temperature for MnFe4Si3 (x=4) [1,2]. We performed macroscopic magnetization measurements in static and pulsed fields which provide a basis to quantify and explain phenomenologically the MCE and to elucidate its anisotropy [3,4]. Crystal structures were investigated using powder and single crystal x-ray and neutron diffraction studies under varying temperatures and pressures [5].Neutron diffraction experiments were of particular importance here as - on one hand - they allow to unambiguously characterize the preferred ordering of Mn and Fe on the two symmetry independent sites available for the paramagnetic ions and thus help elucidating the site dependence of the magnetocaloric effect [6]. On the other hand, they are mandatory for the determination of the magnetic structures in the system [2,6].The underlying spin dynamics of the system was studied by a combination of inelastic neutron scattering and density functional theory calculations [7,8]. The parent compound Mn5Si3 (x=0), undergoes two first order phase transitions to a collinear AFM2 phase (60K<T<100K) and a non-collinear AFM1 phase (T<60K) with the transition from AFM1-AFM2 being related to an inverse MCE. The spin excitation spectrum of the AFM1 phase consists only of propagating spin waves, in contrast to the AFM2 phase where propagative spin waves coexist with diffuse spin fluctuations [9].For the ferromagnetic compound MnFe4Si3 (x=4), which exhibits a direct MCE, we observed a strong anisotropy between in- and out-of-plane magnetic exchange interactions in the magnon spectrum which is also reflected in the q-dependent line-widths in the paramagnetic state. The obtained correlation lengths of this system indicate a short-range order and the in- and out-of-plane spin-fluctuations around Tc are found to be isotropic [10].Furthermore, we performed inelastic neutron scattering investigations under external magnetic field on Mn5Si3 (x=0) and MnFe4Si3 (x=4). We could show that the inverse MCE which is observed in Mn5Si3 is related to field-induced spin fluctuations [9], while on the contrary the direct MCE observed in MnFe4Si3 is associated to the usual suppression of fluctuations by magnetic field [10].[1] D. Songlin et.al., J. Alloys Compd. 334, 249–252 (2002).[2] P. Hering, et al.,Chem. Mater. 27, 7128 (2015)[3] N. Maraytta et.al., J. Alloys Compd. 805, 1161–1167 (2019).[4] N. Maraytta et. Al., J. Appl. Phys. 128, 103903 (2020).[5] A. Eich et.al., Mater. Res. Express 6, 096118 (2019)[6] M. Ait Haddouch et. al., J. Appl. Crystallogr. 55, 1164 (2022)[7] F. J. dos Santos et. al., Phys. Rev. B 103, 024407 (2021).[8] N. Biniskos et. al., Phys. Rev. B 105 104404 (2022).[9] N. Biniskos et. al., Phys. Rev. Letters 120, 257205 (2018).[10] N. Biniskos et. al., Phys. Rev. B 96 104407 (2017).
Keyword(s): Energy (1st) ; Magnetic Materials (1st) ; Condensed Matter Physics (2nd) ; Magnetism (2nd)
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