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@INPROCEEDINGS{Shahed:906820,
      author       = {Shahed, Hend and Sharma, N. and Angst, M. and Voigt, J. and
                      Persson, J. and Törnroos, K. W. and Chernyshov, D. and
                      Englert, U. and Gildenast, H. and Grzechnik, A. and Friese,
                      K.},
      title        = {{E}lucidation of {B}arocaloric {E}ffect in {S}pin
                      {C}rossover {C}ompounds},
      reportid     = {FZJ-2022-01714},
      year         = {2022},
      abstract     = {The search for new efficient materials and refrigeration
                      mechanisms is a key challenge toreplace the conventional
                      vapor compression technology. An attractive alternative
                      technologyuses the caloric refrigeration cycle, which is
                      based on the adiabatic temperature and isothermalentropy
                      change upon tuning an external parameter such as pressure,
                      electric field or magneticfield. Recently, spin crossover
                      (SCO) compounds have been recognized as promising
                      candidates,which exhibit large barocaloric effects: Large
                      isothermal entropy changes have been reportedfor some of
                      these SCO compounds at fairly low hydrostatic pressures (<
                      1.2 GPa) [1]. In SCOcomplexes the central metal ion switches
                      between a low spin (LS) state at low temperature /high
                      pressure and a high spin (HS) state at high temperature /
                      low pressure. The LS to HStransition involves an increase of
                      the spin entropy, but a larger part of the entropy
                      changeoriginates from changes in the intramolecular
                      vibrations [2].In this work, we report on magnetization
                      measurements and single crystal synchrotronradiation
                      diffraction on SCO complexes consisting of Fe+2 as a central
                      ion bound to six nitrogenatoms. Our focus is
                      Fe(PM-Bia)2(NCS)2, PM-Bia =
                      (N-(2′-pyridylmethylene)-4-amino-biphenyl),which
                      crystallizes in two polymorphs depending on thesynthesis
                      route. Polymorph P1 crystallizes orthorhombic(Pccn) and
                      undergoes an abrupt spin transition around 170 K.Polymorph
                      P2 crystallizes monoclinic (P21/c) and undergoes agradual
                      spin transition around 200 K [3].From the structural data,
                      we extracted the temperaturedependence of the Fe-N distances
                      (Figure 1), which can thenbe used to determine the high spin
                      fraction. From the fitting ofthe temperature dependence of
                      the high spin fraction, weobtained the change in entropy
                      (ΔS), the change in enthalpy(ΔH), and the cooperativity
                      (Г). The values obtained for ΔS andΔH on the basis of the
                      structural data are substantiallydifferent from the values
                      of the entropy as deduced from heatcapacity measurements
                      [4]. The width of the transition region,differs strongly
                      between the two polymorphs. This indicatesthe importance of
                      intermolecular interactions for the spintransitions in both
                      polymorphs.},
      month         = {Mar},
      date          = {2022-03-14},
      organization  = {30th annual meeting of the German
                       Crystallographic Society (DGK), Ludwig
                       Maximilians Universität München +
                       online (Germany + online), 14 Mar 2022
                       - 17 Mar 2022},
      cin          = {JCNS-2 / PGI-4 / JARA-FIT},
      cid          = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {632 - Materials – Quantum, Complex and Functional
                      Materials (POF4-632) / 6G4 - Jülich Centre for Neutron
                      Research (JCNS) (FZJ) (POF4-6G4)},
      pid          = {G:(DE-HGF)POF4-632 / G:(DE-HGF)POF4-6G4},
      typ          = {PUB:(DE-HGF)1},
      url          = {https://juser.fz-juelich.de/record/906820},
}