23 research outputs found
Magnetization, crystal structure and anisotropic thermal expansion of single-crystal SrEr2O4
The magnetization, crystal structure, and thermal expansion of a nearly
stoichiometric SrErO single crystal have
been studied by PPMS measurements and in-house and high-resolution synchrotron
X-ray powder diffraction. No evidence was detected for any structural phase
transitions even up to 500 K. The average thermal expansions of lattice
constants and unit-cell volume are consistent with the first-order Gr\"uneisen
approximations taking into account only the phonon contributions for an
insulator, displaying an anisotropic character along the crystallographic
\emph{a}, \emph{b}, and \emph{c} axes. Our magnetization measurements indicate
that obvious magnetic frustration appears below 15 K, and
antiferromagnetic correlations may persist up to 300 K.Comment: 6 pages, 5 figure, 2 table
Incommensurate antiferromagnetic order in the manifoldly-frustrated SrTbO with transition temperature up to 4.28 K
The Nel temperature of the new frustrated family of
Sr\emph{RE}O (\emph{RE} = rare earth) compounds is yet limited to
0.9 K, which more or less hampers a complete understanding of the
relevant magnetic frustrations and spin interactions. Here we report on a new
frustrated member to the family, SrTbO with a record =
4.28(2) K, and an experimental study of the magnetic interacting and
frustrating mechanisms by polarized and unpolarized neutron scattering. The
compound SrTbO displays an incommensurate antiferromagnetic (AFM) order
with a transverse wave vector \textbf{Q} = (0.5924(1),
0.0059(1), 0) albeit with partially-ordered moments, 1.92(6) at
0.5 K, stemming from only one of the two inequivalent Tb sites mainly by virtue
of their different octahedral distortions. The localized moments are confined
to the \emph{bc} plane, 11.9(66) away from the \emph{b} axis probably
by single-ion anisotropy. We reveal that this AFM order is dominated mainly by
dipole-dipole interactions and disclose that the octahedral distortion,
nearest-neighbour (NN) ferromagnetic (FM) arrangement, different next NN FM and
AFM configurations, and in-plane anisotropic spin correlations are vital to the
magnetic structure and associated multiple frustrations. The discovery of the
thus far highest AFM transition temperature renders SrTbO a new
friendly frustrated platform in the family for exploring the nature of magnetic
interactions and frustrations.Comment: 19 pages, 8 Figures, 1 Tabl
Monovalent Ion Condensation at the Electrified Liquid/Liquid Interface
X-ray reflectivity studies demonstrate the condensation of a monovalent ion
at the electrified interface between electrolyte solutions of water and
1,2-dichloroethane. Predictions of the ion distributions by standard
Poisson-Boltzmann (Gouy-Chapman) theory are inconsistent with these data at
higher applied interfacial electric potentials. Calculations from a
Poisson-Boltzmann equation that incorporates a non-monotonic ion-specific
potential of mean force are in good agreement with the data.Comment: 4 pages, 4 figure
Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2 Si2 single crystal
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix
Ion Distributions at Electrified Liquid-Liquid Interfaces: Microscopic and Macroscopic Measurements
An important unsolved problem in the study of ion distributions is the relationship of macroscopic electrochemistry measurements to the ion distribution determined by microscopic synchrotron x-ray scattering measurements. In this work, we present recent x-ray reflectivity and interfacial tension measurements of electrified oil/water interfaces as a function of interfacial electric potential for a series of interfaces between solutions of 10 mM alkali chloride (XCl, where
X is the alkali metal ion of Li+, Na+, Rb+ and Cs+) in water and 5 mM organic supporting electrolyte BTPPATPFB in 1,2-dichloroethane. The potential is established by the use of electrodes and supporting electrolytes in the bulk phases. The impedance spectroscopy as a function of interfacial electric potential was also measured for each interface. The analysis of interfacial tension and impedance spectroscopy measurements were discussed and compared with the results from x-ray reflectivity analysis as well.
Cyclic voltammogram was measured for each interface to determine the working potential range. Interfacial tension measurements were performed using a Cahn microbalance that measures the weight of a Teflon Wilhelmy plate fully submerged in the top water phase to determine the potential of zero charge (PZC) and the capillary wave roughness of the interfaces.
The interfacial excess charge as a function of electric potential was determined from the tension measurements. Impedance spectroscopy was measured for each interface to determine the capacitance as a function of applied electric potentials.
X-ray scattering experiments were carried out at the ChemMatCARS beamline 15-ID at the
Advanced Photon Source (Argonne National Laboratory, USA). Large changes in reflectivity
occur from intermediate potentials for each sample we study. These results disagree with
predictions of the Gouy-Chapman (GC) theory. A Poisson-Boltzmann (PB) calculation that
incorporates a potential of mean force (PMF) to describe the role of liquid structure on the ion
distributions agrees well with the x-ray reflectivity data.
In addition, we calculated the excess interfacial charge from these ion distributions. These
calculated excess interfacial charges from the PB-PMF method are in good agreement with the
tension measurement results. We also calculated the capacitance as a function of applied electric
potentials for each sample from the PB-PMF calculations, and these results only showed limited
agreements with the capacitance yielded from the impedance spectroscopy measurements.
These comparisons make a direct connection between the molecular level x-ray measurements
and macroscopic electrochemistry measurements of interfacial tension and impedance spectroscopy