27 research outputs found
Spin dynamics of FeGaGe studied by Electron Spin Resonance
The intermetallic semiconductor FeGa acquires itinerant ferromagnetism
upon electron doping by a partial replacement of Ga with Ge. We studied the
electron spin resonance (ESR) of high-quality single crystals of
FeGaGe for from 0 up to 0.162 where ferromagnetic order is
observed. For we observed a well-defined ESR signal, indicating the
presence of pre-formed magnetic moments in the semiconducting phase. Upon Ge
doping the occurrence of itinerant magnetism clearly affects the ESR properties
below ~K whereas at higher temperatures an ESR signal as seen in
FeGa prevails independent on the Ge-content. The present results show
that the ESR of FeGaGe is an appropriate and direct tool to
investigate the evolution of 3d-based itinerant magnetism.Comment: 12 pages, 7 figure
Optical signature of Weyl electronic structures in tantalum pnictides Ta ( P, As)
To investigate the electronic structure of Weyl semimetals Ta (P,
As), optical conductivity [] spectra are measured over a wide
range of photon energies and temperatures, and these measured values are
compared with band calculations. Two significant structures can be observed: a
bending structure at 85 meV in TaAs, and peaks at
50 meV (TaP) and 30 meV (TaAs). The bending structure
can be explained by the interband transition between saddle points connecting a
set of Weyl points. The temperature dependence of the peak intensity can
be fitted by assuming the interband transition between saddle points connecting
a set of Weyl points. Owing to the different temperature dependence of
the Drude weight in both materials, it is found that the Weyl points of TaAs
are located near the Fermi level, whereas those of TaP are further away.Comment: 8 pages, 6 figure
Electron Spin Resonance on the spin-1/2 triangular magnet NaYbS2
The delafossite structure of NaYbS2 contains a planar spin-1/2 triangular
lattice of Yb3+ ions and features a possible realisation of a quantum
spin-liquid state. We investigated the Yb3+ spin dynamics by Electron Spin
Resonance (ESR) in single-crystalline samples of NaYbS2. Very clear spectra
with a well-resolved and large anisotropy could be observed down to the lowest
accessible temperature of 2.7 K. In contrast to the ESR properties of other
known spin-liquid candidate systems, the resonance seen in NaYbS2 is accessible
at low fields (< 1T) and is narrow enough for accurate characterisation of the
relaxation rate as well as the g factor of the Yb3+ spins.Comment: 8 page
Electron spin resonance study on the 4f honeycomb quantum magnet YbCl3
The local magnetic properties of Yb in the layered honeycomb material
YbCl were investigated by electron spin resonance on single crystals. For
in-plane and out-of-plane field orientations the -factor shows a clear
anisotropy ( and ), whereas the low temperature
exchange coupling and the spin relaxation display a rather isotropic character.
At elevated temperatures the contribution of the first excited crystal field
level (~meV) dominates the spin relaxation.Comment: 10 pages, 5 figure
Frustrated couplings between alternating spin-1/2 chains in AgVOAsO4
We report on the crystal structure and magnetic behavior of the spin-1/2
compound AgVOAsO4. Magnetic susceptibility, high-field magnetization, and
electron spin resonance measurements identify AgVOAsO4 as a gapped quantum
magnet with a spin gap Delta ~ 13 K and a saturation field H_s ~ 48.5 T.
Extensive band structure calculations establish the microscopic magnetic model
of spin chains with alternating exchange couplings J ~ 40 K and J' ~ 26 K.
However, the precise evaluation of the spin gap emphasizes the role of
interchain couplings which are frustrated due to the peculiar crystal structure
of the compound. The unusual spin model and the low energy scale of the
exchange couplings make AgVOAsO4 a promising candidate for an experimental
investigation of Bose-Einstein condensation and other exotic ground states in
high magnetic fields.Comment: 10 pages + supplementary information and cif files, 7 figures, 6
table
Microwave spectroscopy on heavy-fermion systems: probing the dynamics of charges and magnetic moments
Investigating solids with light gives direct access to charge dynamics,
electronic and magnetic excitations. For heavy fermions, one has to adjust the
frequency of the probing light to the small characteristic energy scales,
leading to spectroscopy with microwaves. We review general concepts of the
frequency-dependent conductivity of heavy fermions, including the slow Drude
relaxation and the transition to a superconducting state, which we also
demonstrate with experimental data taken on UPd2Al3. We discuss the optical
response of a Fermi liquid and how it might be observed in heavy fermions.
Microwave studies with focus on quantum criticality in heavy fermions concern
the charge response, but also the magnetic moments can be addressed via
electron spin resonance (ESR). We discuss the case of YbRh2Si2, the open
questions concerning ESR of heavy fermions, and how these might be addressed in
the future. This includes an overview of the presently available experimental
techniques for microwave studies on heavy fermions, with a focus on broadband
studies using the Corbino approach and on planar superconducting resonators.Comment: 11 pages, 6 figures, proceedings of QCnP 201
Hidden magnetic order in CuNCN
We report a comprehensive experimental and theoretical study of the
quasi-one-dimensional quantum magnet CuNCN. Based on magnetization measurements
above room temperature as well as muon spin rotation and electron spin
resonance measurements, we unequivocally establish the localized Cu+2-based
magnetism and the magnetic transition around 70 K, both controversially
discussed in the previous literature. Thermodynamic data conform to the
uniform-spin-chain model with a nearest-neighbor intrachain coupling of about
2300 K, in remarkable agreement with the microscopic magnetic model based on
density functional theory band-structure calculations. Using exact
diagonalization and the coupled-cluster method, we derive a collinear
antiferromagnetic order with a strongly reduced ordered moment of about 0.4
mu_B, indicating strong quantum fluctuations inherent to this
quasi-one-dimensional spin system. We re-analyze the available
neutron-scattering data, and conclude that they are not sufficient to resolve
or disprove the magnetic order in CuNCN. By contrast, spectroscopic techniques
indeed show signatures of long-range magnetic order below 70 K, yet with a
rather broad distribution of internal field probed by implanted muons. We
contemplate the possible structural origin of this effect and emphasize
peculiar features of the microstructure studied with synchrotron powder x-ray
diffraction.Comment: 17 pages, 17 figures, 1 tabl
Spectroscopic study of the magnetic ground state of NbFe
We have investigated single crystals and polycrystals from the series
NbFe, by electron spin resonance,
muon spin relaxation and M\"ossbauer spectroscopy. Our data establish that at
lowest temperatures all samples exhibit bulk magnetic order. Slight Fe-excess
induces low-moment ferromagnetism, consistent with bulk magnetometry (), Nb--rich and stoichiometric NbFe display spin
density wave order with small magnetic moment amplitudes of the order . This provides microscopic evidence for a
modulated magnetic state on the border of ferromagnetism in NbFe.Comment: 7 pages, 9 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