# Influence of magnetic field, chemical pressure and hydrostatic pressure on the structural and magnetocaloric properties of the Mn–Ni–Ge system

## Abstract

The magnetic, structural and thermomagnetic properties of the MM'X material system of MnNiGe are evaluated with respect to their utilization in magnetocaloric refrigeration. The effects of separate and simultaneous substitution of Fe for Mn and Si on the Ge site are analysed in detail to highlight the benefits of the isostructural alloying method. A large range of compounds with precisely tunable structural and magnetic properties and the tuning of the phase transition by chemical pressure are compared to the effect of hydrostatic pressure on the martensitic transition.

We obtained very large isothermal entropy changes $\Delta S_{\rm iso}$ of up to $-37.8$ J ${\rm kg}^{-1}$ ${\rm K}^{-1}$ based on magnetic measurements for (Mn,Fe)NiGe in moderate fields of 2 T. The enhanced magnetocaloric properties for transitions around room temperature are demonstrated for samples with reduced Ge, a resource critical element. An adiabatic temperature change of 1.3 K in a magnetic field change of 1.93 T is observed upon direct measurement for a sample with Fe and Si substitution. However, the high volume change of 2.8% results in an embrittlement of large particles into several smaller fragments and leads to a sensitivity of the magnetocaloric properties towards sample shape and size. On the other hand, this large volume change enables to induce the phase transition with a large shift of the transition temperature by application of hydrostatic pressure (72 K ${\rm GPa}^{-1}$ ). Thus, the effect of 1.88 GPa is equivalent to a substitution of 10% Fe for Mn and can act as an additional stimulus to induce the phase transition and support the low magnetic field dependence of the phase transition temperature for multicaloric applications.

Item Type: Article 2017 Taubel, Andreas and Gottschall, Tino and Fries, Maximilian and Faske, Tom and Skokov, Konstantin P. and Gutfleisch, Oliver Influence of magnetic field, chemical pressure and hydrostatic pressure on the structural and magnetocaloric properties of the Mn–Ni–Ge system English The magnetic, structural and thermomagnetic properties of the MM'X material system of MnNiGe are evaluated with respect to their utilization in magnetocaloric refrigeration. The effects of separate and simultaneous substitution of Fe for Mn and Si on the Ge site are analysed in detail to highlight the benefits of the isostructural alloying method. A large range of compounds with precisely tunable structural and magnetic properties and the tuning of the phase transition by chemical pressure are compared to the effect of hydrostatic pressure on the martensitic transition. We obtained very large isothermal entropy changes $\Delta S_{\rm iso}$ of up to $-37.8$ J ${\rm kg}^{-1}$ ${\rm K}^{-1}$ based on magnetic measurements for (Mn,Fe)NiGe in moderate fields of 2 T. The enhanced magnetocaloric properties for transitions around room temperature are demonstrated for samples with reduced Ge, a resource critical element. An adiabatic temperature change of 1.3 K in a magnetic field change of 1.93 T is observed upon direct measurement for a sample with Fe and Si substitution. However, the high volume change of 2.8% results in an embrittlement of large particles into several smaller fragments and leads to a sensitivity of the magnetocaloric properties towards sample shape and size. On the other hand, this large volume change enables to induce the phase transition with a large shift of the transition temperature by application of hydrostatic pressure (72 K ${\rm GPa}^{-1}$ ). Thus, the effect of 1.88 GPa is equivalent to a substitution of 10% Fe for Mn and can act as an additional stimulus to induce the phase transition and support the low magnetic field dependence of the phase transition temperature for multicaloric applications. Journal of Physics D: Applied Physics 50 46 IOP Publishing Ltd 11 Department of Materials and Earth Sciences11 Department of Materials and Earth Sciences > Material Science11 Department of Materials and Earth Sciences > Material Science > Functional Materials11 Department of Materials and Earth Sciences > Material Science > Structure Research 27 Dec 2017 09:09 10.1088/1361-6463/aa8e89 https://doi.org/10.1088/1361-6463/aa8e89 Special Issue on Caloric Materials JSONT2T_XMLBibTeXHTML CitationEndNoteRDF+XMLDublin CoreMultiline CSVSimple MetadataMODSASCII CitationAtomReference ManagerEP3 XML TUfind oder in Google
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