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@INPROCEEDINGS{Friese:1005571,
      author       = {Friese, Karen and Schmalzl, Karin and Voigt, Jörg and
                      Biniskos, Nikolaos and Raymond, Stephane and Grzechnik,
                      Andrzej and Santos, Flaviano Jose dos and Brückel, Thomas},
      title        = {{E}lucidating the {M}echanism of the {M}agnetocaloric
                      {E}ffect in {C}ompounds of the {S}eries {M}n5-x{F}ex{S}i3},
      reportid     = {FZJ-2023-01533},
      year         = {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).},
      month         = {Apr},
      date          = {2023-04-10},
      organization  = {Material Research Society Spring
                       Meeting $\&$ Exhibit 2023, San
                       Francisco (USA), 10 Apr 2023 - 14 Apr
                       2023},
      subtyp        = {Invited},
      cin          = {JCNS-FRM-II / IAS-1 / PGI-1 / JARA-FIT / JARA-HPC / JCNS-4
                      / JCNS-ILL / JCNS-2 / MLZ},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)IAS-1-20090406 / I:(DE-Juel1)PGI-1-20110106 /
                      $I:(DE-82)080009_20140620$ / $I:(DE-82)080012_20140620$ /
                      I:(DE-Juel1)JCNS-4-20201012 / I:(DE-Juel1)JCNS-ILL-20110128
                      / I:(DE-Juel1)JCNS-2-20110106 / I:(DE-588b)4597118-3},
      pnm          = {6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ)
                      (POF4-6G4) / 632 - Materials – Quantum, Complex and
                      Functional Materials (POF4-632) / 5211 - Topological Matter
                      (POF4-521)},
      pid          = {G:(DE-HGF)POF4-6G4 / G:(DE-HGF)POF4-632 /
                      G:(DE-HGF)POF4-5211},
      experiment   = {EXP:(DE-Juel1)ILL-IN12-20150421},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/1005571},
}