scholarly journals Lattice disorder effect on magnetic ordering of iron arsenides

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Athena S. Sefat ◽  
Xiaoping P. Wang ◽  
Yaohua Liu ◽  
Qiang Zou ◽  
Mimgming Fu ◽  
...  
Keyword(s):  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Structural Features ◽  
Lattice Parameter ◽  
Chemical Compositions ◽  
Lattice Disorder ◽  
Local Lattice ◽  
Higher Temperature ◽  
Disordered Crystal ◽  
Planar Strain

AbstractThis study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the locally disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.

The limits of strain and lattice parameter measurements by CBED

1989 ◽  
Vol 47 ◽  
pp. 518-519
Author(s):  
Hamish L. Fraser
Keyword(s):  
Electron Beam ◽  
Mirror Symmetry ◽  
Local Symmetry ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Surface Relaxation ◽  
Strained Layer ◽  
Axis Parallel ◽  
Local Lattice ◽  
Strained Layer Superlattice

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.

scholarly journals Data-driven studies of magnetic two-dimensional materials

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Trevor David Rhone ◽  
Wei Chen ◽  
Shaan Desai ◽  
Steven B. Torrisi ◽  
Daniel T. Larson ◽  
...  
Keyword(s):  
Machine Learning ◽  
Dft Calculations ◽  
Density Functional ◽  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Magnetic Behavior ◽  
Data Driven ◽  
Two Dimensional ◽  
Computationally Efficient ◽  
Data Driven Approach

Abstract We use a data-driven approach to study the magnetic and thermodynamic properties of van der Waals (vdW) layered materials. We investigate monolayers of the form $$\hbox {A}_2\hbox {B}_2\hbox {X}_6$$ A 2 B 2 X 6 , based on the known material $$\hbox {Cr}_2\hbox {Ge}_2\hbox {Te}_6$$ Cr 2 Ge 2 Te 6 , using density functional theory (DFT) calculations and machine learning methods to determine their magnetic properties, such as magnetic order and magnetic moment. We also examine formation energies and use them as a proxy for chemical stability. We show that machine learning tools, combined with DFT calculations, can provide a computationally efficient means to predict properties of such two-dimensional (2D) magnetic materials. Our data analytics approach provides insights into the microscopic origins of magnetic ordering in these systems. For instance, we find that the X site strongly affects the magnetic coupling between neighboring A sites, which drives the magnetic ordering. Our approach opens new ways for rapid discovery of chemically stable vdW materials that exhibit magnetic behavior.

scholarly journals Spontaneous Magnetization and Optical Activity in the Chiral Series {(L-proline)nV[Cr(CN)6]x} (0 < n < 3)

2020 ◽  
Vol 6 (1) ◽  
pp. 12
Author(s):  
Bárbara Rodríguez-García ◽  
Jose Ramon Galan-Mascaros
Keyword(s):  
Spectroscopic Data ◽  
Room Temperature ◽  
Spontaneous Magnetization ◽  
Magnetic Hysteresis ◽  
Magnetic Ordering ◽  
Structural Features ◽  
Natural Amino Acid ◽  
Amorphous Nature ◽  
Redox Stability ◽  
Circular Dichroic

The incorporation of the natural amino acid L-proline in the synthesis to vanadium-chromium Prussian blue derivatives results in materials exhibiting magnetic ordering including chiral magnetic centers. Although the amorphous nature of these materials makes difficult to assess the structural features of these proline-containing compounds, magnetic and spectroscopic data confirms their multifunctionality. They exhibit high-temperature magnetic ordering (Tc < 255 K) and a circular dichroic signal, representing the molecule-based chiral magnets with the highest ordering temperatures reported to date. In addition, the presence of chiral L-proline (or D-proline) has additional benefits, including higher redox stability and the appearance of magnetic hysteresis. The latter was not observed in the parent compounds, the series of room temperature molecule-based magnets V[Cr(CN)6]x.

scholarly journals Plasma-Assisted Chemical Vapor Deposition of F-Doped MnO2 Nanostructures on Single Crystal Substrates

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1335
Author(s):  
Lorenzo Bigiani ◽  
Chiara Maccato ◽  
Alberto Gasparotto ◽  
Cinzia Sada ◽  
Elza Bontempi ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Data Storage ◽  
Vapor Deposition ◽  
Oxygen Deficiency ◽  
Chemical Vapor ◽  
Magnetic Ordering ◽  
Analytical Techniques ◽  
Structural Features ◽  
Optical Absorption Spectroscopy ◽  
Magnetic Characteristics

MnO2 nanostructures were fabricated by plasma assisted-chemical vapor deposition (PA-CVD) using a fluorinated diketonate diamine manganese complex, acting as single-source precursor for both Mn and F. The syntheses were performed from Ar/O2 plasmas on MgAl2O4(100), YAlO3(010), and Y3Al5O12(100) single crystals at a growth temperature of 300 °C, in order to investigate the substrate influence on material chemico-physical properties. A detailed characterization through complementary analytical techniques highlighted the formation of highly pure and oriented F-doped systems, comprising the sole β-MnO2 polymorph and exhibiting an inherent oxygen deficiency. Optical absorption spectroscopy revealed the presence of an appreciable Vis-light harvesting, of interest in view of possible photocatalytic applications in pollutant degradation and hydrogen production. The used substrates directly affected the system structural features, as well as the resulting magnetic characteristics. In particular, magnetic force microscopy (MFM) measurements, sensitive to the out-of-plane magnetization component, highlighted the formation of spin domains and long-range magnetic ordering in the developed materials, with features dependent on the system morphology. These results open the door to future engineering of the present nanostructures as possible magnetic media for integration in data storage devices.

A comparative study of Li10.35Ge1.35P1.65S12 and Li10.5Ge1.5P1.5S12 superionic conductors

2020 ◽  
Vol 13 (06) ◽  
pp. 2050031
Author(s):  
Yue Jiang ◽  
Zhiwei Hu ◽  
Ming’en Ling ◽  
Xiaohong Zhu
Keyword(s):  
Ionic Conductivity ◽  
Room Temperature ◽  
Ionic Conductivities ◽  
Lithium Ion ◽  
Lattice Parameter ◽  
Superionic Conductors ◽  
Chemical Compositions ◽  
Temperature Conductivity ◽  
Room Temperature Conductivity ◽  
Ion Conductor

Since the lithium-ion conductor Li[Formula: see text]GeP2S[Formula: see text] (LGPS) with a super high room-temperature conductivity of 12[Formula: see text]mS/cm was first reported in 2011, sulfide-type solid electrolytes have been paid much attention. It was suggested by Kwon et al. [J. Mater. Chem. A 3, 438 (2015)] that some excess lithium ions in LGPS, namely, Li[Formula: see text]Ge[Formula: see text] P[Formula: see text]S[Formula: see text], could further improve their ionic conductivities, and the highest conductivity of 14.2[Formula: see text]mS/cm was obtained at [Formula: see text] though a larger lattice parameter that occurred at [Formula: see text]. In this study, we focus on these two different chemical compositions of LGPS with [Formula: see text] and [Formula: see text], respectively. Both samples were prepared using the same experimental process. Their lattice parameter, microstructure and room-temperature ionic conductivity were compared in detail. The results show that the main phase is the tetragonal LGPS phase but with a nearly identical amount of orthorhombic LGPS phase coexisting in both samples. Bigger lattice parameters, larger grain sizes and higher ionic conductivities are simultaneously achieved in Li[Formula: see text]Ge[Formula: see text]P[Formula: see text]S[Formula: see text] ([Formula: see text]), exhibiting an ultrahigh room-temperature ionic conductivity of 18.8[Formula: see text]mS/cm.

Local Lattice Parameter Determination of Strained Areas of Semiconductors Using CBED

2004 ◽  
Vol 10 (S02) ◽  
pp. 310-311
Author(s):  
Takayuki Akaogi ◽  
Kenji Tsuda ◽  
Masami Terauchi ◽  
Michiyoshi Tanaka
Keyword(s):  
Lattice Parameter ◽  
Parameter Determination ◽  
Local Lattice

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Chemical reaction at the interface between (Hg0.9Re0.1)Ba2CaCu2Oy thin film and SrTiO3 substrate

2001 ◽  
Vol 16 (1) ◽  
pp. 256-260 ◽  
Author(s):  
Xiao-Jing Wu ◽  
N. Inoue ◽  
T. Sugano ◽  
T. Morishita ◽  
K. Tanabe
Keyword(s):  
Chemical Reaction ◽  
Electron Microscopic Observation ◽  
Lattice Parameter ◽  
Electron Microscopic ◽  
Step Process ◽  
Srtio3 Substrate ◽  
Transmission Electron ◽  
Transmission Electron Microscopic Observation ◽  
Transmission Electron Microscopic ◽  
Higher Temperature

c-Axis-oriented (Hg0.9Re0.1)Ba2CaCu2Oy thin films were grown on the (100) plane of SrTiO3 substrates by a so-called two-step process. Transmission electron microscopic observation revealed that, in the film annealed under a higher temperature, some steplike regions appeared at the top layer of SrTiO3 substrate. High-resolution transmission electron microscopic images showed that the lattice parameters in these regions are about 4.05–4.15 Å, being longer than the lattice parameter of SrTiO3. It is supposed that a chemical reaction occurred in these regions, and a phase of (Bax,Sr1−x)(Cuy,Ti1−y)O3δs was formed by partially substituted Ba for Sr and Cu for Ti.

Tuning of Gadolinium Based Compounds for Potential Application in Self-Controlled Hyperthermia Treatment of Cancer

2010 ◽  
Vol 442 ◽  
pp. 242-249 ◽  
Author(s):  
S.N. Ahmad ◽  
S.A. Shaheen
Keyword(s):  
Magnetic Materials ◽  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Invasive Technique ◽  
Hyperthermia Treatment ◽  
Non Invasive ◽  
Ferromagnetic Bulk ◽  
Constituent Elements ◽  
Curie Temperature Tc ◽  
Potential Use

We report on the synthesis and investigation of magnetic properties of several new Gd based alloys suitable for their potential use in self-controlled hyperthermia treatment of cancer. Self-controlled hyperthermia is a non-invasive technique that employs heating of magnetic materials (ferromagnetic bulk sized thermo-seeds or magnetic nanoparticles) in a. c. fields to cure cancer cells. Magnetic materials with Curie temperature (Tc) in the range of 40-46oC are desired, as decreased magnetic coupling in paramagnetic regime (above Tc) provides a safeguard against overheating of normal cells. The need for developing such materials was dictated by the lack of existing magnetic materials with magnetic ordering temperature in the suitable range of hyperthermia applications. This study shows that these materials have high magnetization values and their Tc values can be varied linearly over a broad range by adjusting the composition of the constituent elements.

Arrangement of C atoms in the SiC–C solid solution

1999 ◽  
Vol 55 (3) ◽  
pp. 297-305 ◽  
Author(s):  
O. O. Mykhaylyk ◽  
M. P. Gadzira
Keyword(s):  
Solid Solution ◽  
Point Defects ◽  
Strain Field ◽  
Field Model ◽  
Fine Powder ◽  
Lattice Parameter ◽  
Acta Cryst ◽  
Planar Defects ◽  
X Ray ◽  
Higher Temperature

The microstructure of a silicon carbide–carbon solid-solution powder (SiC–C), obtained from a fine powder of silicon and thermal expansive graphite, is investigated by X-ray powder diffraction methods. The microstructure is characterized by Williamson–Hall analysis and the strain-field model suggested by van Berkum et al. [Acta Cryst. (1996), A52, 730–747]. SiC–C adopts a layered structure like the solid solutions formed by compounds possessing a diamond-like structure, e.g. SiC–AlN. Superstoichiometric C atoms are located as planar defects. The SiC–C solid solution is destroyed on heating in a vacuum in the temperature range of graphitization of diamond but is maintained after sintering at high pressure (4–8 GPa) and high temperature (1673 and 2073 K). However, at the higher temperature (2073 K), it is observed that planar defects formed by C atoms decompose to non-correlated point defects accompanied simultaneously by a decrease in the lattice parameter from 4.3540 (2) to 4.35234 (5) Å.

Hydrothermal synthesis and structure determination of a new calcium iron ruthenium hydrogarnet

2018 ◽  
Vol 73 (11) ◽  
pp. 803-811 ◽  
Author(s):  
Hagen Poddig ◽  
Jens Hunger ◽  
Sirko Kamusella ◽  
Hans-Henning Klauss ◽  
Thomas Doert
Keyword(s):  
Hydrothermal Synthesis ◽  
Tetrahedral Site ◽  
Magnetic Ordering ◽  
Lattice Parameter ◽  
Partial Substitution ◽  
Alkaline Conditions ◽  
Approximate Composition ◽  
Calcium Iron ◽  
Charge Balancing

AbstractA new calcium iron ruthenium hydrogarnet with the approximate composition Ca3(Ru2−xFex)(FeO4)2−y(H4O4)1+y (x=1, y≈0.35) has been obtained by hydrothermal synthesis under oxidizing alkaline conditions. The compound crystallizes in the cubic space group Ia3̅d (No. 230) with a lattice parameter of a=12.4804(4) Å (T=100 K) and Z=8. The octahedral site of the garnet structure is equally occupied by Ru and Fe, whereas the tetrahedral site is partially occupied by Fe only. A partial substitution of the oxide anions by hydroxide ions is necessary for charge balancing, corresponding to the so-called hydrogarnet defects. The presence of hydroxide groups is proven by infrared spectroscopy. 57Fe Mössbauer spectroscopic data provide evidence for two different Fe3+ coordination environments as well as a magnetic ordering of two iron substructures with the respective ordering temperature above room temperature. The crystal composition was verified by energy-dispersive X-ray spectroscopy and the thermal behavior of the calcium iron ruthenate was studied by difference thermal analysis.

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