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@BOOK{ChogondahalliMuniraju:22244,
      author       = {Chogondahalli Muniraju, Naveen Kumar},
      title        = {{C}rystal and spin structure and their relation to physical
                      properties in some geometrical and spin spiral multiferoics},
      volume       = {44},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-22244},
      isbn         = {978-3-89336-802-0},
      series       = {Schriften des Forschungszentrums Jülich.
                      Schlüsseltechnologien / Key Technologies},
      pages        = {III, 190 S.},
      year         = {2012},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {The aim of the present work has been to synthesize and to
                      investigate crystal and spin structure in some geometrical
                      and spin spiral multiferroics. Multiferroic materials
                      exhibit two or more ferroic properties such as,
                      ferroelectricity, ferromagnetism and ferroelasticity. These
                      materials are considered as prime candidates for future
                      computer data storage and spintronics. There are several
                      classes of magnetoelectric multiferroics classified based on
                      the origin of multiferroicity. The two types of multiferroic
                      compounds investigated in the present dissertation are,
                      geometrically frustrated systems including; hexagonal
                      DyMnO$_{3}$ (hDMO) and orthorhombic HoCrO$_{3}$ (HCO) and
                      spin spiral systems including wolframite type
                      Mn$_{0.9}$Co$_{0.1}$WO$_{4}$ (MCoW) and
                      Mn$_{0.9}$Cu$_{0.1}$WO$_{4}$ (MCuW). The samples were
                      characterized by macroscopic techniques; specific heat and
                      magnetization as well as microscopic techniques; x-ray
                      diffraction and neutron scattering. Polycrystalline samples
                      of HCO were prepared by solid state reaction method and the
                      phase purity is confirmed by x-ray diffraction measurements.
                      From magnetization measurements we determined magnetic
                      ordering temperature and also an indication of
                      antiferromagnetic exchange interactions is found. In
                      isothermal magnetization measurements a hysteretic behavior
                      was observed indicating the presence of ferromagnetism. Two
                      magnetic field induced transitions is also found from
                      isothermal magnetization measurements. The thermal
                      properties of HCO can be very well described in terms of
                      lattice, hyperfine and crystal field interaction
                      contributions. From the specific heat data the contributions
                      from lattice, hyperfine and crystal field interactions was
                      determined. The hyperfine field at Ho site and the hyperfine
                      splitting energy are deduced. Using a Schottky formula for
                      multiple crystal field levels, five crystal field energies
                      were computed. Magnetic ordering of both Cr and and Ho
                      moments in HCO was determined by neutron powder diffraction
                      (NPD) measurements. The Cr magnetic moments order
                      antiferromagnetically with a small canting angle about
                      crystallographic z-direction while the ordering of Ho
                      moments is a induced type. Ho orders antiferromagnetically
                      within ab-plane with weak ferromagnetic component along
                      $\textit{b}$-direction. The thermal variation of Cr and Ho
                      ordered moments was understood based on molecular field (MF)
                      theory. The obtained molecular field constants reveals that
                      Cr–Cr interactions are stronger compared to Ho–Cr
                      interactions. The lowest crystal field splitting energy
                      obtained from MF theory is in good agreement with the value
                      obtained from specific heat and inelastic neutron scattering
                      (INS) measurements. NPD data also indicated the presence of
                      spin fluctuations which was confirmed by INS measurements.
                      From INS data the correlation length of short range ordering
                      was calculated using Selyakov-Scherrer formula. [...]},
      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)3},
      url          = {https://juser.fz-juelich.de/record/22244},
}