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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},
}