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@PHDTHESIS{Gottschlich:22832,
      author       = {Gottschlich, Michael},
      title        = {{S}tructure, magnetism and excitations in some {M}n-based
                      magnetocaloric effect compounds},
      volume       = {62},
      school       = {RWTH Aachen},
      type         = {Dr. (FH)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-22832},
      isbn         = {978-3-89336-874-7},
      series       = {Schriften des Forschungszentrums Jülich.
                      Schlüsseltechnologien / Key Technologies},
      pages        = {175 S.},
      year         = {2012},
      note         = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
                      2012},
      abstract     = {The magnetocaloric effect causes the cooling or heating of
                      a material due to the influence of an applied magnetic
                      field. This mechanism provides an alternative technique for
                      cooling, when using cheap and environment friendly
                      materials. Heating and cooling takes place without moving
                      any mechanical parts. Therefore, this effect attracts the
                      attention of many scientific studies. The magneto caloric
                      effect is characterized by the entropy change.
                      Polycrystalline samples of the compositions
                      Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=0,1,2,3,4 and a single
                      crystal of the composition Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=4
                      were prepared in order to analyze the magnetocaloric effect
                      in those materials. All samples were characterized with
                      magnetization measurements. Ferroand antiferromagnetic
                      behaviour could be detected. Diffraction patterns were taken
                      on the timeof- flight powder diffractometer POWGEN at the
                      Spallation Neutron Source (SNS), Oak Ridge National
                      Laboratory to analyze the magnetic structures of the
                      compounds. Inelastic neutron data were collected on the
                      single crystal Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=4 on the
                      thermal neutron triple axis spectrometer 2T1 at Laboratoire
                      Léon Brillouin to investigate the dynamic properties. The
                      refined data taken on samples Mn$_{5−x}$Fe$_{x}$Si$_{3}$
                      x=0,1,2,3,4 on POWGEN at room temperature confirm the
                      hexagonal structure. This has already been reported in
                      literature. Anomalies could be identified in several
                      crystallographic parameters as funtion of the Fe-content of
                      the samples Diffraction patterns taken on sample
                      Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=0 between the phase
                      transitions at 70K and 90K could be refined with an
                      orthorhombic unit cell including antiferromagnetism. Below
                      the phase transition at 62K the best refinements could be
                      performed using a monoclinic unit cell. Also, the structure
                      seems to exhibit weak ferromagnetism, which can be
                      annihilated with an applied magnetic field. This mechanism
                      is proposed to cause the negative magnetocaloric effect in
                      this compound. The analysis of diffraction patterns taken in
                      the ferromagnetic phase of Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=4
                      indicate different behaviours of the magnetic atoms
                      occupying the two crystallographic positions (the third is
                      occupied by Si). This property is proposed to influence
                      significantly the entropy in this material. Phonon branches
                      in the dispersion relation of Mn$_{5−x}$Fe$_{x}$Si$_{3}$
                      x=4 are anisotropic, which is due to the hexagonal
                      structure. In order to investigate the effect of Fe and Mn
                      on the change of the entropy the composition
                      Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=4 was doped with Co (for Mn
                      and Fe). The analysis of the diffraction patterns which were
                      taken on POWGEN identified at least one impurity phase in
                      every sample. Different behaviours of the magnetic moments
                      of the atoms in these compounds could also be verified,
                      which is similar to the composition
                      Mn$_{5−x}$Fe$_{x}$Si$_{3}$ x=4.},
      cin          = {PGI-4 / JCNS-2 / JARA-FIT},
      cid          = {I:(DE-Juel1)PGI-4-20110106 / I:(DE-Juel1)JCNS-2-20110106 /
                      $I:(DE-82)080009_20140620$},
      pnm          = {Grundlagen für zukünftige Informationstechnologien},
      pid          = {G:(DE-Juel1)FUEK412},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/22832},
}