The histogram shows that the values of change in entropy (ΔSmax), relative cooling power (RCP), and Curie temperature (Tc) for current samples (La0.90Zr0.10MnO3) are simultaneously enhanced and are ...comparable with the family of La-manganite materials and standard gadolinium (Gd) bulk sample. The dotted orange line shows the room temperature. The inset shows the table with serial number and the corresponding materials with their respective references. (Note: ΔSmax and RCP values are taken at ΔH = 5T).
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•La1−xZrxMnO3 (x = 0.05, 0.10 and 0.15) samples synthesized by chemical combustion.•Magnetic transition near-room-temperature with the second-order phase transition.•Short-range exchange interactions help in enhanced magnetic and magnetocaloric values.•Change in entropy |ΔSm| at 5 T is 4.04 J·kg−1·K−1 at 304 K for La0.90Zr0.10MnO3 sample.•Potential material for future magnetic refrigeration works at near room-temperature.
Near-room-temperature and enhanced magnetocaloric properties are investigated for the chemical combustion synthesized electron-doped manganite La1−xZrxMnO3 with x = 0.05, 0.10 and 0.15. The single-phase rhombohedral crystal structure is observed particularly for the La0.90Zr0.10MnO3 (Zr10) system. Importantly, all the samples exhibit the paramagnetic-to-ferromagnetic (PM-to-FM) transition close to the room-temperature with the second-order phase transition. The analysis of the magnetic data in the critical region with different theoretical models such as 3D-Heisenberg, 3D-Ising, Mean-field, and Tri-critical mean-field suggested that the Zr10 sample exhibits the typical 3D-Heisenberg ferromagnetic characteristics. This indicated that the enhanced magnetic and magnetocaloric properties are governed by short-range exchange forces. Furthermore, the obtained data is also fitted with the Kouvel-Fisher method to obtain the transition-temperature, critical exponent β and it is found that the transition temperature and β values are totally consistent to that of the 3D-Heisenberg model. Significantly, the change in entropy |ΔSm| at 5 T is calculated to be 4.04 J·kg−1·K−1 at 304 K in case of Zr10 sample indicating that it can be one of the potential material for the future magnetic refrigeration technology working at near room-temperature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mn2SnS4 belongs to the M2IIAIVQ4 (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic ...properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn2SnS4 quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at ∼37 K and another at ∼152 K. However, in Fe-substituted Mn2SnS4 samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn2SnS4) to 174 K (Mn1.82Fe0.18SnS4) is observed. The increase in the antiferromagnetic ordering temperature in Mn2−xFexSnS4 may be attributed to the increase in the covalence of Mn/Fe–S–Mn/Fe bonds (shorter) with iron substitution.
Composites with promising electrical and magnetic properties have dragged the attention of the current research interest as compared to the single-phase material due to their potential applications ...in sensor and charge storage devices. Hence, composites (1−
x
)Bi
5
Ti
3
FeO
15
−(
x
)La
0.67
Sr
0.33
MnO
3
with different compositions (
x
= 0, 0.1, 0.2, 0.3, and 0.4) are investigated via the sol–gel precursor hybrid method. The structural analysis and phase purity of the composites are examined by the Rietveld refinement of X-ray diffraction spectra. This reveals the existence of the Bragg peaks corresponding to the perovskite (BTFO) as well as the manganite (LSMO) phase. The strain at the interface of the BTFO and LSMO phases causes the change in lattice parameters and shifting of phonon modes in the Raman spectra. X-ray photoelectron spectroscopy (XPS) confirms the mixed-valence state of Mn
3+
/Mn
4+
and Fe
3+
/Fe
2+
ions, endorsing the oxygen vacancies in the prepared composites. The dielectric permittivity increases with the increase of the LSMO phase, which is ascribed to interfacial lattice strain. Using the modified Debye model, the dispersive behavior of frequency-dependent dielectric permittivity is explained. Room temperature M–H data reveal the enhancement of
M
r
(~4.74 × 10
–3
emu/g) by 13 times and
M
max
(~ 0.415 emu/g) by 6 times for 40% LSMO composite which is ascribed to the inclusion of the manganite (LSMO) phase. Theoretically, the magnetization value is also estimated from Vegard’s law and compared with the experimental result.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
To describe the clinical manifestations and outcomes of critically ill children with coronavirus disease-19 (COVID-19) in New York City.
Retrospective observational study of children 1 month to ...21 years admitted March 14 to May 2, 2020, to 9 New York City pediatric intensive care units (PICUs) with severe acute respiratory syndrome coronavirus 2 infection.
Of 70 children admitted to PICUs, median age was 15 (IQR 9, 19) years; 61.4% male; 38.6% Hispanic; 32.9% black; and 74.3% with comorbidities. Fever (72.9%) and cough (71.4%) were the common presenting symptoms. Twelve patients (17%) met severe sepsis criteria; 14 (20%) required vasopressor support; 21 (30%) developed acute respiratory distress syndrome (ARDS); 9 (12.9%) met acute kidney injury criteria; 1 (1.4%) required renal-replacement therapy, and 2 (2.8%) had cardiac arrest. For treatment, 27 (38.6%) patients received hydroxychloroquine; 13 (18.6%) remdesivir; 23 (32.9%) corticosteroids; 3 (4.3%) tocilizumab; and 1 (1.4%) anakinra; no patient was given immunoglobulin or convalescent plasma. Forty-nine (70%) patients required respiratory support: 14 (20.0%) noninvasive mechanical ventilation, 20 (28.6%) invasive mechanical ventilation (IMV), 7 (10%) prone position, 2 (2.8%) inhaled nitric oxide, and 1 (1.4%) extracorporeal membrane oxygenation. Nine (45%) of the 20 patients requiring IMV were extubated by day 14 with median IMV duration of 218 (IQR 79, 310.4) hours. Presence of ARDS was significantly associated with duration of PICU and hospital stay, and lower probability of PICU and hospital discharge at hospital day 14 (P < .05 for all).
Critically ill children with COVID-19 predominantly are adolescents, have comorbidities, and require some form of respiratory support. The presence of ARDS is significantly associated with prolonged PICU and hospital stay.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Tetragonal distorted CuMn
2
O
4
spinel has been prepared by a single-step method and its complex dielectric, impedance, and electric modulus measured with respect to frequency at different selected ...temperatures. In all the measurements, a frequency-dependent inflection point was observed above 170 K, revealing the cross-over in the grain and grain boundary effects in the electrical properties. Therefore, the activation energy was calculated to be
E
a
≈
0.27
eV
from the dielectric loss but as
E
a
≈
0.2
eV
from the impedance and electric modulus based on the Arrhenius nature of the relaxation time. Further, alternating-current (AC) conductivity measurements in the frequency range from 100 Hz to 1 MHz suggested hoping conduction due to small polarons.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Among MII2AIVQ4 (M = transition metal; A = Si, Ge, and Sn; Q = S, Se, and Te)-type compounds, most of which crystallize in an olivine or spinel structure, Mn2SnS4 is a unique compound that ...crystallizes in the orthorhombic space group Cmmm and exhibits complex magnetic properties. In this article, we report synthesis and study of the effect of Sb substitution (up to 20%) on the magnetic properties of Mn2SnS4. All the compounds were found to be in a single phase and indexed with the orthorhombic parent structure. Rietveld refinement of the room-temperature neutron diffraction data of Mn2Sn0.85Sb0.15S4 sample shows that Sb occupies the Mn site by replacing an equivalent amount of Mn. Subsequently, the replaced Mn occupies the Sn site causing disorder at both the Mn and the Sn sites, and the refined composition (Mn1.85(1)Sb0.15(1))(Sn0.85(1)Mn0.15(1))S4 is obtained. Although the purpose of incorporation of Sb(iii) was to create a mixed valence state at the Mn site, XPS study shows contrasting results. Sb exists in a mixed valence state, Sb(iii) and Sb(v), which balances the charge at the Sn(iv) site. Magnetic study of the compounds shows a very interesting trend. Pure Mn2SnS4 shows two magnetic transitions: one at 152 K that corresponds to antiferromagnetic ordering and other at 53 K corresponding to weak ferromagnetic ordering possibly due to spin canting. With antimony substitution, the temperature (152 K) of antiferromagnetic ordering remains unchanged, whereas the temperature of weak ferromagnetic ordering gradually increases with an increase in the Sb content from 53 K for the undoped compound to 88 K for 20% Sb-doped Mn2SnS4. The increase in the temperature of weak ferromagnetic ordering could be attributed to the incorporation of Sb, which induces more disorder at the Mn site, thereby making the magnetic lattice dilute with reduced frustration.
Herein we reported the crystal structure and crystal chemistry of orthorhombic perovskite type Nd2CuTiO6 in between 2 K and 290 K as observed from the in situ temperature-dependent powder neutron ...diffraction (PND) studies. It is observed that the cations in octahedral sites are statistically occupied, and the ambient temperature orthorhombic structure is retained throughout the temperature range of the study. Absence of any long-range magnetic ordering down to 2 K is confirmed by both low-temperature PND and magnetization studies. The lattice shows strong anisotropic thermal expansion with increasing temperature, viz. almost no or feeble negative expansion along the a-axis while appreciably larger expansion along the other two axes (αb = 10.6 × 10−6 K−1 and αc = 9.8 × 10−6 K−1). A systematic change in the rotation of octahedral units with temperature was observed in the studied temperature range, while the expansion of unit cells is predominantly associated with the polyhedral units around the Nd3Ions. The temperature-dependent relative change in unit cell parameters as well as coefficients of axial thermal expansion show anomalous behavior at lower temperatures, and that seems to be related to the electronic contributions to lattice expansion.
The observation of a metallic interface between band insulators La Al O3 and Sr Ti O3 has led to massive efforts to understand the origin of the phenomenon as well as to search for other systems ...hosting such two-dimensional electron gases (2-DEGs). However, the understanding of the origin of the 2-DEG is very often hindered as several possible mechanisms such as polar catastrophe, cationic intermixing, and oxygen vacancy (OV) can be operative simultaneously. The presence of a heavy element makes the K Ta O3 (KTO) based 2-DEG a potential platform to investigate spin-orbit coupling driven novel electronic and magnetic phenomena. In this work, we investigate the sole effect of OV in KTO, which makes KTO metallic. O K-edge x-ray absorption spectroscopy measurements find that OV dopes electrons in Ta t*2g antibonding states. Photoluminescence measurements reveal the existence of a highly localized deep midgap state in oxygen-deficient KTO. Our detailed ab initio calculations demonstrate that such deep midgap state arises due to the linear clustering of OVs around Ta. Our present work emphasizes that we must pay attention to the possible presence of OVs in interpreting emergent behavior of KTO-based heterostructures.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
The goal of this study was to compare two approaches for MR-based PET patient attenuation correction (AC) in whole-body FDG-PET imaging using a tri-modality PET/CT and MR setup. Sixteen clinical ...whole-body FDG patients were included in this study. Mean standard uptake values (SUVs) were measured for liver and lung volumes-of-interest for comparison. Maximum SUVs were measured in 18 FDG-avid features in 10 of the patients. The AC methods compared to gold-standard CT-based AC were segmentation of the CT (air, lung, fat, water), MR image segmentation with four tissue classes (air, lung, fat, water), and segmentation with air, lung and a continuous fat/water method. Results show that magnitude differences of the uptake values induced by CT-based image segmentation were similar but lower on average than those found using MR-derived AC methods. The average liver SUV difference as compared to using CTAC was 1.3%, 10.4%, and 5.7% for 4-class segmented CT, 4-class MRAC, and continuous fat/water MRAC methods, respectively. The average FDG-avid feature SUVmax difference was -0.5%, 1.7%, and -1.6% for 4-class segmented CT, 4-class MRAC, and continuous fat/water MRAC methods, respectively. The results demonstrated that both 4-class and continuous fat/water AC methods provided adequate quantitation in the body, and that the continuous fat/water method was within 5.7% on average for SUVmean in liver and 1.6% on average for SUVmax for FDG-avid features.
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