580 research outputs found
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
H - T phase diagram of YbCo2Si2 with H // [100]
We report on the first high-resolution dc-magnetisation () measurements on
a single crystal of \ycs. was measured down to 0.05 K and in fields up to
12 T, with the magnetic field parallel to the crystallographic direction
[100]. Two antiferromagnetic (AFM) phase transitions have been detected in a
field T at K and K, in form of a
sharp cusp and a sudden drop in , respectively. These signatures
suggest that the phase transitions are order at and
order at . The upper transition is suppressed by a critical field
T. The field-dependent magnetisation shows two hysteretic
metamagnetic-like steps at the lowest temperature, followed by a sharp kink,
which separates the AFM region from the paramagnetic one. The magnetic
phase diagram of \ycs has been deduced from the isothermal and isofield curves.
Four AFM regions were identified which are separated by and
order phase-transition lines.Comment: 5 Pages, 3 figure
Magnetic order and spin dynamics across a ferromagnetic quantum critical point: SR investigations of YbNi(PAs)
In the quasi-1D heavy-fermion system YbNi(PAs) the
presence of a ferromagnetic (FM) quantum critical point (QCP) at with unconventional quantum critical exponents in the thermodynamic
properties has been recently reported. Here, we present muon-spin relaxation
(SR) experiments on polycrystals of this series to study the magnetic
order and the low energy 4-electronic spin dynamics across the FM QCP. The
zero field SR measurements on pure YbNi(P proved static long
range magnetic order and suggested a strongly reduced ordered Yb moment of
about 0.04. With increasing As substitution the ordered moment is
reduced by half at and to less than 0.005 at . The
dynamic behavior in the SR response show that magnetism remains
homogeneous upon As substitution, without evidence for disorder effect. In the
paramagnetic state across the FM QCP the dynamic muon-spin relaxation rate
follows 1/ with . The critical fluctuations are very slow and are even becoming slower
when approaching the QCP.Comment: 6 pages, 4 figure
Quantum Griffiths phase in CePd(1-x)Rh(x) with x ~ 0.8
The magnetic field dependence of the magnetisation () and the temperature
dependence of the ac susceptibility () of CePd(1-x)Rh(x) single
crystals with are analysed within the frame of the
quantum Griffiths phase scenario, which predicts and
with . All vs and
vs data follow the predicted power-law behaviour. The parameter
, extracted from , is very sensitive to the Rh content
and varies systematically with from -0.1 to 0.4. The value of ,
derived from measurements on a \cpr single crystal, seems to be rather
constant, , in a broad range of temperatures between 0.05
and 2 K and fields up to about 10 T. All observed signatures and the
values are thus compatible with the quantum Griffiths scenario.Comment: 4 pages, 3 figure
Avoided ferromagnetic quantum critical point: Unusual short-range ordered state in CeFePO
Cerium 4f electronic spin dynamics in single crystals of the heavy-fermion
system CeFePO is studied by means of ac-susceptibility, specific heat and
muon-spin relaxation (SR). Short-range static magnetism occurs below the
freezing temperature Tg ~ 0.7 K, which prevents the system from accessing the
putative ferromagnetic quantum critical point. In the SR, the
sample-averaged muon asymmetry function is dominated by strongly inhomogeneous
spin fluctuations below 10 K and exhibits a characteristic time-field scaling
relation expected from glassy spin dynamics, strongly evidencing cooperative
and critical spin fluctuations. The overall behavior can be ascribed neither to
canonical spin glasses nor other disorder-driven mechanisms.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letters, Link:
http://prl.aps.org/accepted/6207bYdaGef1483c419928305372ce2d4419eb96
Huge First-Order Metamagnetic Transition in the Paramagnetic Heavy-Fermion System CeTiGe
We report on the observation of large, step-like anomalies in the
magnetization (\,/Ce), in the magnetostriction
(), and in the magnetoresistance in
polycrystals of the paramagnetic heavy-fermion system CeTiGe at a critical
magnetic field 12.5\,T at low temperatures. The size of
these anomalies is much larger than those reported for the prototypical
heavy-fermion metamagnet CeRuSi. Furthermore, hysteresis between
increasing and decreasing field data indicate a real thermodynamic, first-order
type of phase transition, in contrast to the crossover reported for
CeRuSi. Analysis of the resistivity data shows a pronounced decrease of
the electronic quasiparticle mass across . These results establish CeTiGe
as a new metamagnetic Kondo-lattice system, with an exceptionally large,
metamagnetic transition of first-order type at a moderate field.Comment: 5 pages, 4 figure
Magnetic phase diagram of YbCo2Si2 derived from magnetization measurements
We report on high-resolution dc-magnetization (M) measurements on a
high-quality single crystal of YbCo2Si2. M was measured down to 0.05K and in
fields up to 4T, with the magnetic field oriented along the crystallographic
directions [100], [110] and [001] of the tetragonal structure
Evolution of magnetism in Yb(Rh_(1-x)Co_x)2Si2
We present a study of the evolution of magnetism from the quantum critical
system YbRh2Si2 to the stable trivalent Yb system YbCo2Si2. Single crystals of
Yb(Rh_(1-x)Co_x)2Si2 were grown for 0 < x < 1 and studied by means of magnetic
susceptibility, electrical resistivity, and specific heat measurements, as well
as photoemission spectroscopy. The results evidence a complex magnetic phase
diagram, with a non-monotonic evolution of T_N and two successive transitions
for some compositions resulting in two tricritical points. The strong
similarity with the phase diagram of YbRh2Si2 under pressure indicates that Co
substitution basically corresponds to the application of positive chemical
pressure. Analysis of the data proves a strong reduction of the Kondo
temperature T_K with increasing Co content, T_K becoming smaller than T_N for x
~ 0.5, implying a strong localization of the 4f electrons. Furthermore,
low-temperature susceptibility data confirm a competition between ferromagnetic
and antiferromagnetic exchange. The series Yb(Rh_(1-x)Co_x)2Si2 provides an
excellent experimental opportunity to gain a deeper understanding of the
magnetism at the quantum critical point in the vicinity of YbRh2Si2 where the
antiferromagnetic phase disappears (T_N=>0).Comment: 11 pages, 9 figure
Evidence for a Kondo destroying quantum critical point in YbRh2Si2
The heavy-fermion metal YbRhSi is a weak antiferromagnet below
K. Application of a low magnetic field T () is sufficient to continuously suppress the antiferromagnetic (AF) order.
Below K, the Sommerfeld coefficient of the electronic specific
heat exhibits a logarithmic divergence. At K, (), while the electrical resistivity
(: residual resistivity). Upon
extrapolating finite- data of transport and thermodynamic quantities to , one observes (i) a vanishing of the "Fermi surface crossover" scale
, (ii) an abrupt jump of the initial Hall coefficient and
(iii) a violation of the Wiedemann Franz law at , the field-induced
quantum critical point (QCP). These observations are interpreted as evidence of
a critical destruction of the heavy quasiparticles, i.e., propagating Kondo
singlets, at the QCP of this material.Comment: 20 pages, 8 figures, SCES 201
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