1,267 research outputs found
Weak magnetic anisotropy in GdRhSi studied by magnetic resonance
The antiferromagnetically (AFM) ordered state of GdRhSi which
consists of AFM-stacked ferromagnetic layers is investigated by magnetic
resonance spectroscopy. The almost isotropic Gd paramagnetic resonance
becomes anisotropic in the AFM ordered region below 107 K. The emerging
internal anisotropic exchange-fields are still small enough to allow an
investigation of their magnetization dynamics by using a standard
microwave-frequency magnetic resonance technique. We could characterize this
anisotropy in detail in the ferromagnetic layers of the excitation at 9 and 34
GHz. We derived a resonance condition for the AFM ordered phase to describe the
weak in-plane anisotropic behaviour in combination with a mean-field analysis.Comment: 7 page
GdRhSi: An exemplary tetragonal system for antiferromagnetic order with weak in-plane anisotropy
The anisotropy of magnetic properties commonly is introduced in textbooks
using the case of an antiferromagnetic system with Ising type anisotropy. This
model presents huge anisotropic magnetization and a pronounced metamagnetic
transition and is well-known and well-documented both, in experiments and
theory. In contrast, the case of an antiferromagnetic - system with weak
in-plane anisotropy is only poorly documented. We studied the anisotropic
magnetization of the compound GdRhSi and found that it is a perfect
model system for such a weak-anisotropy setting because the Gd ions in
GdRhSi have a pure spin moment of S=7/2 which orders in a simple AFM
structure with . We observed experimentally in a
continuous spin-flop transition and domain effects for field applied along the
- and the -direction, respectively. We applied a mean field model
for the free energy to describe our data and combine it with an Ising chain
model to account for domain effects. Our calculations reproduce the
experimental data very well. In addition, we performed magnetic X-ray
scattering and X-ray magnetic circular dichroism measurements, which confirm
the AFM propagation vector to be and indicate the absence of
polarization on the rhodium atoms
Anisotropic Zeeman Splitting in YbNi4P2
The electronic structure of heavy-fermion materials is highly renormalised at
low temperatures with localised moments contributing to the electronic
excitation spectrum via the Kondo effect. Thus, heavy-fermion materials are
very susceptible to Lifshitz transitions due to the small effective Fermi
energy arising on parts of the renormalised Fermi surface. Here, we study
Lifshitz transitions that have been discovered in YbNi4P2 in high magnetic
fields. We measure the angular dependence of the critical fields necessary to
induce a number of Lifshitz transitions and find it to follow a simple
Zeeman-shift model with anisotropic g-factor. This highlights the coherent
nature of the heavy quasiparticles forming a renormalised Fermi surface. We
extract information on the orientation of the Fermi surface parts giving rise
to the Lifshitz transitions and we determine the anisotropy of the effective
g-factor to be in good agreement with the crystal field
scheme of YbNi4P2.Comment: 10 pages, 5 figures, prepared for resubmission to SciPos
Time-resolved collapse and revival of the Kondo state near a quantum phase transition
One of the most successful paradigms of many-body physics is the concept of
quasiparticles: excitations in strongly interacting matter behaving like weakly
interacting particles in free space. Quasiparticles in metals are very robust
objects. Yet, when a system's ground state undergoes a qualitative change at a
quantum critical point (QCP), the quasiparticles may disintegrate and give way
to an exotic quantum-fluid state of matter. The nature of this breakdown is
intensely debated, because the emergent quantum fluid dominates the material
properties up to high temperature and might even be related to the occurence of
superconductivity in some compounds. Here we trace the dynamics of
heavy-fermion quasiparticles in CeCuAu and monitor their
evolution towards the QCP in time-resolved experiments, supported by many-body
calculations. A terahertz pulse disrupts the many-body heavy-fermion state.
Under emission of a delayed, phase-coherent terahertz reflex the heavy-fermion
state recovers, with a coherence time 100 times longer than typically
associated with correlated metals. The quasiparticle weight collapses towards
the QCP, yet its formation temperature remains constant -- phenomena believed
to be mutually exclusive. Coexistence in the same experiment calls for
revisions in our view on quantum criticality.Comment: Published version, including data on CeCu6, CeCu5.9Au0.1, and
CeCu5Au1 and extended Supplementary Information. 7 pages, 4 figures,
Supplementary Information: 5 pages, 3 figure
Cascade of magnetic field induced Lifshitz transitions in the ferromagnetic Kondo lattice material YbNi4P2
A ferromagnetic quantum critical point is thought not to exist in two and
three-dimensional metallic systems yet is realized in the Kondo lattice
compound YbNi4(P,As)2, possibly due to its one-dimensionality. It is crucial to
investigate the dimensionality of the Fermi surface of YbNi4P2 experimentally
but common probes such as ARPES and quantum oscillation measurements are
lacking. Here, we studied the magnetic field dependence of transport and
thermodynamic properties of YbNi4P2. The Kondo effect is continuously
suppressed and additionally we identify nine Lifshitz transitions between 0.4
and 18 T. We analyze the transport coefficients in detail and identify the type
of Lifshitz transitions as neck or void type to gain information on the Fermi
surface of YbNi4P2. The large number of Lifshitz transitions observed within
this small energy window is unprecedented and results from the particular flat
renormalized band structure with strong 4f-electron character shaped by the
Kondo lattice effect.Comment: 6 pages, 4 figure
Kondo-lattice ferromagnets and their peculiar order along the magnetically hard axis
We show that Ce- and Yb-based Kondo-lattice ferromagnets order mainly along
the magnetically hard direction of the ground state Kramers doublet determined
by crystalline electric field (CEF). Here we argue that this peculiar
phenomenon, that was believed to be rare, is instead the standard case.
Moreover, it seems to be independent on the Curie temperature ,
crystalline structure, size of the ordered moment and type of ground state wave
function. On the other hand, all these systems show the Kondo coherence maximum
in the temperature dependence of the resistivity just above
which indicates a Kondo temperature of a few Kelvin. An important role of
fluctuations is indicated by the non-mean-field like transition in specific
heat measurements as well as by the suppression of this effect by a strong
Ising-like anisotropy. We discuss possible theoretical scenarios
Electro-nuclear transition into a spatially modulated magnetic state in YbRhSi
The nature of the antiferromagnetic order in the heavy fermion metal
YbRhSi, its quantum criticality, and superconductivity, which appears
at low mK temperatures, remain open questions. We report measurements of the
heat capacity over the wide temperature range 180 K - 80 mK, using current
sensing noise thermometry. In zero magnetic field we observe a remarkably sharp
heat capacity anomaly at 1.5 mK, which we identify as an electro-nuclear
transition into a state with spatially modulated electronic magnetic order of
maximum amplitude 0.1. We also report results of measurements in
magnetic fields in the range 0 to 70 mT, applied perpendicular to the c-axis,
which show eventual suppression of this order. These results demonstrate a
coexistence of a large moment antiferromagnet with putative superconductivity.Comment: 11 pages, 11 figures, including the supplementary informatio
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