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@PHDTHESIS{Feng:858704,
      author       = {Feng, Erxi},
      title        = {{M}agnetic {O}rder and {E}xcitation in {F}rustrated
                      {P}yrochlore 5d - {T}ransition {M}etal {O}xides},
      volume       = {187},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2018-07549},
      isbn         = {978-3-95806-365-5},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Schlüsseltechnologien / Key Technologies},
      pages        = {IV, 182 S.},
      year         = {2018},
      note         = {RWTH Aachen, Diss., 2018},
      abstract     = {Motivated by the recent experimental realizations of novel
                      magnetic phases and emergent quasiparticles, such as
                      magnetic monopoles and Majorana fermions, in frustrated and
                      topological quantum magnets, this thesis focuses on the
                      studies of the magnetic ground state of a complete series of
                      pyrochlore 5d transition metal oxides, including the
                      Ln$_{2}$Ir$_{2}$O$_{7}$ (Ln =rare-earth elements) family and
                      Nd$_{2}$Hf$_{2}$O$_{7}$, via in-house specific heat and
                      magnetization measurements as well as advanced neutron
                      scattering techniques. This has allowed us to establish a
                      global phase diagram of the magnetic ground state of
                      Ln$_{2}$Ir$_{2}$O$_{7}$. Except for Pr$_{2}$Ir$_{2}$O$_{7}$,
                      other pyrochlore iridates exhibit a transition at finite
                      temperature from a paramagnetic metal to an
                      antiferromagnetic semimetal with the “all-in-all-out”
                      magnetic order of the Ir$^{4+}$ sublattice. The magnetic
                      ground-state of Ln$^{3+}$ is strongly dependent on the
                      Ln$^{3+}$ single-ion anisotropy and the molecular magnetic
                      field generated by the surrounding Ir$^{4+}$ sublattice. For
                      the Ln$^{3+}$ ions with an easy-axis anisotropy along the
                      local [1 1 1] axis, which is parallel to the molecular
                      field, an “all-in-all-out” long-range magnetic order is
                      universally observed on the Ln$^{3+}$ sublattice. On the
                      contrary, for the Ln$^{3+}$ ions with an easy plane
                      anisotropy, a dynamic spin liquid phase persists down to the
                      sub-Kelvin temperature range. Furthermore, aided by the
                      magnetic structure refinements, sum-rule analysis of the
                      total magnetic moments, quantitative analyses of
                      low-temperature magnetic entropy and simulations of
                      inelastic neutron scattering spectra, a deeper understanding
                      on the exotic magnetic order and emergent quantum
                      excitations in the ground state of two representative 5d
                      pyrochlore compounds, the metallic spin-ice
                      Pr$_{2}$Ir$_{2}$O$_{7}$ and insulating quantum spin-ice
                      candidate Nd$_{2}$Hf$_{2}$O$_{7}$, have been obtained.
                      Pr$_{2}$Ir$_{2}$O$_{7}$ undergoes a magnetic transition from
                      paramagnetic state to the “2-in-2-out” long-range order
                      of Pr$^{3+}$ below 0.76 K, signalized by a slightly
                      dispersive gapped magnetic excitation.
                      Nd$_{2}$Hf$_{2}$O$_{7}$ shows an “all-in-all-out”
                      longrange order of Nd$^{3+}$ below 0.53 K. Its magnetic
                      excitation consists of a flat band modecentered at 0.1 meV
                      and a dispersive mode up to 0.23 meV in the ordered state.
                      The XYZ model based on the “dipole-octupole”
                      ground-state doublet is introduced to explain these
                      observations. The Occurrence of exotic quantum fragmentation
                      of magnetic moments in Nd$_{2}$Hf$_{2}$O$_{7}$ can thus be
                      confirmed.},
      cin          = {JCNS-FRM-II / JCNS-2},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106},
      pnm          = {524 - Controlling Collective States (POF3-524) / 6212 -
                      Quantum Condensed Matter: Magnetism, Superconductivity
                      (POF3-621) / 6G15 - FRM II / MLZ (POF3-6G15) / 6G4 - Jülich
                      Centre for Neutron Research (JCNS) (POF3-623)},
      pid          = {G:(DE-HGF)POF3-524 / G:(DE-HGF)POF3-6212 /
                      G:(DE-HGF)POF3-6G15 / G:(DE-HGF)POF3-6G4},
      experiment   = {EXP:(DE-MLZ)DNS-20140101 / EXP:(DE-MLZ)SPODI-20140101 /
                      EXP:(DE-MLZ)TOF-TOF-20140101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/858704},
}