With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba(1-x)K(x)Fe(2)As(2). In agreement with the predicted transition from a single-Q to a double-Q AF structure, we found that a distinct spin density wave develops in the t-AF phase. The pair breaking peak of this spin density wave acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity. We also observed additional phonon modes in the t-AF phase which likely arise from a Brillouin-zone folding that is induced by the double-Q magnetic structure with two Fe sublattices exhibiting different magnitudes of the magnetic moment.
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http://dx.doi.org/10.1103/PhysRevLett.115.027003 | DOI Listing |
Materials (Basel)
July 2022
Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan.
We investigated the superconductivity of (TMTTF)TaF (TMTTF: tetramethyl-tetrathiafulvalene) by conducting resistivity measurements under high pressure up to 8 GPa. A cubic anvil cell (CAC) pressure generator, which can produce hydrostatic high-pressure, was used for this study. Since the generalized temperature-pressure (-) diagram of (TMTF) ( = Se, S, : monovalent anion) based on (TMTTF)PF ( = 70 K and spin-Peierls: SP, = 15 K) was proposed by Jérome, exploring superconductivity states using high-pressure measurement beyond 4 GPa has been required to confirm the universality of the electron-correlation variation under pressure in (TMTTF) (TMTTF)TaF, which has the largest octahedral-symmetry counter anion TaF in the (TMTTF) series, possesses the highest charge-ordering (CO) transition temperature ( = 175 K) in (TMTTF) and demonstrates an anti-ferromagnetic transition ( = 9 K) at ambient pressure.
View Article and Find Full Text PDFJ Magn Reson Imaging
November 2022
Unité de Médecine Interne (UF 04): CRMR MATHEC, Maladies Auto-Immunes et Thérapie Cellulaire, Centre de Référence des Maladies Auto-Immunes Systémiques Rares d'Ile-de-France, FAI2R, Hôpital Saint-Louis, Assistance Publique des Hôpitaux de Paris, Paris, France.
Background: Heart involvement is frequent although often clinically silent in systemic sclerosis (SSc) patients. Early identification of cardiac involvement can be improved by noninvasive methods such as MRI, in addition to transthoracic echocardiography (TTE).
Purpose: To assess the ability of phase-contrast (PC)-MRI to detect subclinical left (LV) and right (RV) ventricular diastolic dysfunction in SSc patients.
Sensors (Basel)
April 2020
School of Electronics and Communication Engineering, Sun Yat-sen University, Guangzhou 510275, China.
This paper considers the coherent integration problem for moving target detection using frequency agile (FA) radar, involving range cell migration (RCM) and the nonuniform phase fluctuations among different pulses caused by range-agile frequency (R-AF) coupling and velocity-time-agile frequency (V-T-AF) coupling. After the analysis of the term corresponding to the phase fluctuation caused by V-T-AF coupling, the term can be regarded as related to an equivalent non-uniform slow time, and nonuniform fast Fourier transform (NUFFT) could be the solution. So a fast coherent integration method combining Radon Fourier transform (RFT) and NUFFT based on low-rank approximation, i.
View Article and Find Full Text PDFPhilos Trans A Math Phys Eng Sci
May 2020
Institute of Continuous Media Mechanics, UB RAS, Academician Korolev Street 1, Perm 614068, Russia.
The problem of magnetic transitions between the low-temperature (macrospin ordered) phases in two-dimensional XY arrays is addressed. The system is modelled as a plane structure of identical single-domain particles arranged in a square lattice and coupled by the magnetic dipole-dipole interaction; all the particles possess a strong easy-plane magnetic anisotropy. The basic state of the system in the considered temperature range is an antiferromagnetic (AF) stripe structure, where the macrospins (particle magnetic moments) are still involved in thermofluctuational motion: the superparamagnetic blocking temperature is lower than that () of the AF transition.
View Article and Find Full Text PDFPhys Rev Lett
July 2015
University of Fribourg, Department of Physics and Fribourg Center for Nanomaterials, Chemin du Musée 3, CH-1700 Fribourg, Switzerland.
With infrared spectroscopy we investigated the spin-reorientation transition from an orthorhombic antiferromagnetic (o-AF) to a tetragonal AF (t-AF) phase and the reentrance of the o-AF phase in the superconducting state of underdoped Ba(1-x)K(x)Fe(2)As(2). In agreement with the predicted transition from a single-Q to a double-Q AF structure, we found that a distinct spin density wave develops in the t-AF phase. The pair breaking peak of this spin density wave acquires much more low-energy spectral weight than the one in the o-AF state which indicates that it competes more strongly with superconductivity.
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