132 research outputs found
Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2
We have investigated the magnetic ground state of the antiferromagnetic
Kondo-lattice compounds CeMAlSi (M = Rh, Ir) using neutron powder
diffraction. Although both of these compounds show two magnetic transitions
and in the bulk properties measurements, evidence for
magnetic long-range order was only found below the lower transition .
Analysis of the diffraction profiles reveals a commensurate antiferromagnetic
structure with a propagation vector = (0, 0, 1/2). The magnetic
moment in the ordered state of CeRhAlSi and CeIrAlSi
were determined to be 1.14(2) and 1.41(3) /Ce, respectively, and are
parallel to the crystallographic -axis in agreement with magnetic
susceptibility measurements
Reduction of the ordered magnetic moment in YMnO3 with hydrostatic pressure
YMnO3 exhibits a ferroelectric transition at high temperature (~ 900 K) and
magnetic ordering at T_N ~ 70 K where the dielectric constant shows an anomaly
indicative of the magneto-dielectric effect. Here we report powder neutron
diffraction experiments in this compound that show that the magnetic moment at
saturation is reduced by application of hydrostatic pressure. Our results yield
further insight about the nature of the spin-lattice interaction in ferroic
materials
Electrodynamics of the antiferromagnetic phase in URuSi
We present data on the optical conductivity of
URu(Fe,Os)Si. While the parent material URuSi
enters the enigmatic hidden order phase below 17.5 K, an antiferromagnetic
phase is induced by the substitution of Fe or Os onto the Ru sites. We find
that both the HO and the AFM phases exhibit an identical gap structure that is
characterized by a loss of conductivity below the gap energy with spectral
weight transferred to a narrow frequency region just above the gap, the typical
optical signature of a density wave. The AFM phase is marked by strong
increases in both transition temperature and the energy of the gap associated
with the transition. In the normal phase just above the transition the optical
scattering rate varies as . We find that in both the HO and the AFM
phases, our data are consistent with elastic resonant scattering of a Fermi
liquid. This indicates that the appearance of a coherent state is a necessary
condition for either ordered phase to emerge. Our measurements favor models in
which the HO and the AFM phases are driven by the common physics of a
nesting-induced density-wave-gap
Ferromagnetic quantum critical point in UCo1-xFexGe
We have carried out a comprehensive study of the UCo1-xFexGe series across
the entire range of compositions 0 <= x <= 1, and report the results of x-ray
diffraction, magnetization, specific heat, and electrical resistivity to
uncover the T-x phase diagram. Substitution of Fe into UCoGe initially results
in an increase in the Curie temperature and a rapid destruction of the
superconductivity. Near x = 0.22, the ferromagnetic transition is suppressed to
zero temperature at an apparent ferromagnetic itinerant electron quantum
critical point, where the temperature dependence of the electrical resistivity
and specific heat in this region reveal non-Fermi liquid behavior.Comment: 7 pages, 7 figure
Noncentrosymmetric Commensurate Magnetic Ordering of Multiferroic ErMn2O5
The non-centrosymmetric magnetic structure of ErMnO has been shown to
be very similar to that of HoMnO (Vecchini {\it et al.}, 2008 Phys.
Rev. B {\bf 77} 134434). The magnetic modulation at 25 K has propagation vector
=(1/2,0,1/4) and the symmetry imposes very few constraints on the
magnetic configurations allowed. Only by combining the results of bulk
magnetisation measurements, powder and single crystal neutron diffraction and
spherical neutron polarization analysis was it possible to distinguish clearly
between different models. The susceptibility measurements show that the erbium
magnetic moments are aligned parallel to the c-axis indicating strong
single-ion anisotropy. Spherical neutron polarimetry demonstrates the presence
of two unequally populated chirality domains in ErMnO single crystals.
X-ray diffraction measurements on an ErMnO powder using synchrotron
radiation show that the buckling angles of the Mn-O-Mn bond change below the
transition to the ferroelectric phase
The magnitude of the magnetic exchange interaction in the heavy fermion antiferromagnet CeRhIn
We have used high-resolution neutron spectroscopy experiments to determine
the complete spin wave spectrum of the heavy fermion antiferromagnet
CeRhIn. The spin wave dispersion can be quantitatively reproduced with a
simple - model that also naturally explains the magnetic spin-spiral
ground state of CeRhIn and yields a dominant in-plane nearest-neighbor
magnetic exchange constant = 0.74 meV. Our results pave the way to a
quantitative understanding of the rich low-temperature phase diagram of the
prominent CeIn ( = Co, Rh, Ir) class of heavy fermion materials.Comment: 7 pages, 3 figure
Elasticity in the skyrmion phase unveils depinning at ultra-low current densities
Controlled movement of nano-scale stable magnetic objects has been proposed
as the foundation for a new generation of magnetic storage devices. Magnetic
skyrmions, vortex-like spin textures stabilized by their topology are
particularly promising candidates for this technology. Their nanometric size
and ability to be displaced in response to an electrical current density
several orders of magnitude lower than required to induce motion of magnetic
domain walls suggest their potential for high-density memory devices that can
be operated at low power. However, to achieve this, skyrmion movement needs to
be controlled, where a key question concerns the coupling of skyrmions with the
underlying atomic lattice and disorder (pinning). Here, we use Resonant
Ultrasound Spectroscopy (RUS), a probe highly sensitive to changes in the
elastic properties, to shed new light on skyrmion elasticity and depinning in
the archetypal skyrmion material MnSi. In MnSi, skyrmions form a lattice that
leads to pronounced changes in the elastic properties of the atomic lattice as
a result of magneto-crystalline coupling. Without an applied current, the shear
and compressional moduli of the underlying crystal lattice exhibit an abrupt
change in the field-temperature range where skyrmions form. For current
densities exceeding the changes of elastic properties vanish, signaling
the decoupling of skyrmion and atomic lattices. Interestingly, , which
we identify as the onset of skyrmion depinning, is about 20 times smaller than
previously measured via non-linear Hall effect. Our results suggest the
presence of a previously-undetected intermediate dynamic regime possibly
dominated by skyrmion-creep motion with important consequences for potential
applications.Comment: 7+4 pages, 4+3 figures, 0+1 tabl
Chemical pressure tuning of URuSi via isoelectronic substitution of Ru with Fe
We have used specific heat and neutron diffraction measurements on single
crystals of URuFeSi for Fe concentrations 0.7 to
establish that chemical substitution of Ru with Fe acts as "chemical pressure"
as previously proposed by Kanchanavatee et al. [Phys. Rev. B {\bf 84},
245122 (2011)] based on bulk measurements on polycrystalline samples. Notably,
neutron diffraction reveals a sharp increase of the uranium magnetic moment at
, reminiscent of the behavior at the "hidden order" (HO) to large moment
antiferromagnetic (LMAFM) phase transition observed at a pressure
0.5-0.7~GPa in URuSi. Using the unit cell volume determined from our
measurements and an isothermal compressibility GPa for URuSi, we determine the chemical pressure
in URuFeSi as a function of . The resulting
temperature -chemical pressure phase diagram for
URuFeSi is in agreement with the established temperature
-external pressure phase diagram of URuSi.Comment: 7 pages, 3 figure
Electronic Correlation and Magnetism in the Ferromagnetic Metal Fe3GeTe2
Motivated by the search for design principles of rare-earth-free strong
magnets, we present a study of electronic structure and magnetic properties of
the ferromagnetic metal Fe3GeTe2 within local density approximation (LDA) of
the density functional theory, and its combination with dynamical mean-field
theory (DMFT). For comparison to these calculations, we have measured magnetic
and thermodynamic properties as well as X-ray magnetic circular dichroism and
the photoemission spectrum of single crystal Fe3GeTe2. We find that the
experimentally determined Sommerfeld coefficient is enhanced by an order of
magnitude with respect to the LDA value. This enhancement can be partially
explained by LDA+DMFT. In addition, the inclusion of dynamical electronic
correlation effects provides the experimentally observed magnetic moments, and
the spectral density is in better agreement with photoemission data. These
results establish the importance of electronic correlations in this
ferromagnet.Comment: 6 pages, 5 eps embedded eps figures. Physical Review B, accepted
versio
Nuclear magnetic resonance studies of pseudospin fluctuations in URuSi
We report Si NMR measurements in single crystals and aligned powders
of URuSi in the hidden order and paramagnetic phases. The
spin-lattice-relaxation data reveal evidence of pseudospin fluctuations of U
moments in the paramagnetic phase. We find evidence for partial suppression of
the density of states below 30 K, and analyze the data in terms of a two
component spin-fermion model. We propose that this behavior is a realization of
a pseudogap between the hidden order transition and 30 K. This
behavior is then compared to other materials that demonstrate precursor
fluctuations in a pseudogap regime above a ground state with long-range order.Comment: 5 pages, 3 figure
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