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Abstract

This review describes in brief recent magnetic resonance imaging (MRI) methods for assessing cardiac structure in healthy and pathologic state using diffusion-weighted (DW) and diffusion tensor imaging (DTI) approaches. A background on the theory and MR pulse sequences employed in DW/DT imaging is given, along with the calculation of diffusion tensor (D), apparent diffusion coefficient (ADC) and fractional anisotropy (FA). Parametric maps derived from DW/DT images can quantify microstructure alterations due to fibrotic collagen deposition, along with associated changes in cardiac muscle anisotropy. Representative examples of ADC and FA parametric maps are shown from ex vivo high-resolution DT images of explanted healthy and scarred hearts obtained from pre-clinical investigations. Furthermore, examples of fiber tractography demonstrating DTI-based 3D (three-dimensional) reconstruction of fiber directions within the heart are illustrated using advanced open-source software. Lastly, future developments and potential translation of DW/DT methods into routine clinical evaluation for cardiac MR imaging protocols are highlighted.

Abstract

Fluorides-based perovskites are currently the typical materials being used in spintronic devices, optoelectronic and magneto-resistance colossal fields. Solar cells made of Fluoro-perovskite hold much promise for the future of solar energy. The electronic structure and magnetic properties of KFeF3, KCoF3 and KNiF3 Fluorides are studied using ab initio Calculation. We have analysed the structural phases, total and partial electronic densities and band structures within the (DFT) vs the DFT+U description. We show the Electro-Magnetic Behavior using L(S)DA+U vs L(S)DA in a comparative study of cation effect by integrating three types of crystal structures (Cubic (Pm-3m), Four-Layered Hexagonal (P6/mmc), and Orthorhombic (Pnma)). Equilibrium lattices agree very well with experimental and theoretical data. Magnetic moment of each phase is discussed. The obtained results confirmed that the three crystal structures invested here exhibit Ferromagnetic (FM) behavior. The introduction of the Hubbard’s parameter U increases lattice parameters and magnetic moment. We deduce that the second cation plays an important role in the magnetic effects. L(S)DA+U show correctly that KFeF3, KCoF3 and KNiF3 are insulators.

Abstract

In this paper, we have studied the electronic, elastic and thermoelectric properties of the half-Heusler LiCrZ (Z = C, N, Si, and P) materials in Type II phase, in this structure the atomic occupations are X (1/2,1/2,1/2), Y (0,0,0) and Z(1/4,1/4,1/4). The ferromagnetic state of Type II structure was found to be the most stable phase for all studied alloys. After calculating the elastic constants, we found out that the conditions of mechanical stability were verified only for LiCrSi and LiCrP alloys in Type II phase, at both equilibrium a0 and half metallic ahm lattice constants, which indicates that these two compounds can be synthesized experimentally. We should also mention that the half metallic behavior in Type II structure, for LiCrSi and LiCrP compounds, was obtained by straining the equilibrium lattice constants by 2% and 6%, respectively. At ahm, these two systems were identified to be true half metals due to their complete spin polarization and integer value of total magnetic moment. These last ones have reached 3μB per unit cell when Z = Si, and 4μB when Z = P. Using the mean field approximation (MFA), the Curie temperatures of Type II structure were also determined, where the values are estimated to be 456.2 K and 302.8 K, respectively. Finally, the thermoelectric performance has been explored by the classical Boltzmann theory. At low temperatures, the figure of merit has reached 0.73 and 0.93 for LiCrSi and LiCrP, respectively. The considerable ZT values and all calculated physical properties make these two systems promising candidates for thermoelectric applications.

Abstract

The search for a new material with unparalleled properties has attracted the interest of the scientific community due to rapid development of technology and it can be very inspiring to the future experiments. In this paper, electronic structure and optical properties of the new rare earth coinage-metal chalconegides YCuChO (Ch=S, Se, Te) are investigated in detail using state-of-the art density functional theory (DFT). Both the GGA-PBEsol and TB-mBJ functionals were used to describe the exchange-correlation interactions. These compounds are novel and have not been synthesized before. The optimized structural parameters, viz., lattice parameters and atomic position coordinates, are predicted. The analyses of the electronic properties indicate that the studied compounds are wide direct bandgap semiconductors. The calculated bandgaps varying from 1.69 eV (for the Te compound) to 2.5 eV (for the S compound) with the mBJ approach. Moreover, the optical properties of these compounds were comprehensively studied and discussed in terms of the dielectric function and loss function. The results provide theoretical support for the exploration of YCuChO (Ch=S, Se, Te) materials in potential optoelectronic applications.

Abstract

The structural, electronic and magnetic properties of (Cubic Pm-3m, Hexagonal-4H, orthorhombic Pnma, and orthorhombic Pbnm) phases of AFeF3 Fluorides (A = Cs, Na, and Rb) are reported theoretically using full potential linearized augmented plane waves method within the density functional theory (DFT). Using different exchange–correlation approximations including the generalized gradient approximation (PBE-GGA, WC-GGA, and PBEsol-GGA), also (GGA) with Hubbard potential (GGA + U) and The modified Becke Johnson potential (mBJ), we carried to determine various physical properties. The Calculations revealing that the estimated structural parameters are reliable with the experimentally reported data. Magnetically all these intermetallics are Ferromagnetic (FM). The ground-state energy of different magnetic phases studied showed that the magnetic moments are evaluated per atom, and overestimated by (GGA+U). Transfer charge reveals a strong covalent interaction between Fe-Fe atoms. Their electronic band structure and density of states indicate insulator behavior.

Abstract

Ab initio calculations of BiFeO3 magnetic perovskite are carried. Accurate density functional theory calculations were performed considering a U-Hubbard correction (DFT+U) to account for on-site Coulomb interactions of the 3d-Fe states. We have applied the Full-potential linearized augmented plane waves (FP-LAPW) method. Exchange-correlation effects are treated using the Local Spin Density approximation (L(S)DA+U) vs generalized gradient approximations (GGA+U). Equilibrium lattices agree very well with other theoretical and experimental data. The magnetization energy differences between Spin Up and Spin Dn states are small. Spin effect and magnetic moment obtained from subsequent (L(S)DA+U) and (GGA+U) calculations are also discussed in different magnetic configurations: The Ferromagnetic cubic phase (Pm-3m), The A-type Antiferromagnetic (P4/mmc) and The G-type Antiferromagnetic (Fm-3m). The nature of magnetism arises mainly from the Fe-site exhibiting a G-type antiferromagnetic ordering. The electronic structure shows that BiFeO3 has a metallic band gap. This multiferroic exhibit strong hybridization of the 3d-Fe and 2p-O orbitals. Therefore, the Multiferroic BiFeO3 perovskite has driven significant research interest due to their promising technological potential. It’s a good candidate for potential applications in spintronic, and to aid the development of the next generation of data storage and multi-functional technological devices.

Abstract

In this work, copper doped nickel oxide as the thin films have been elaborated by a spin coating method, the nickel chloride hexahydrate (0.8M) and copper (II) chloride dehydrate (Cu/Ni = 0, 2.15, 4.3, 8.6 and 12.9 At.%) were used to prepare the Cu doped NiO thin films. The Cu doped NiO thin films were heated at a crystallization temperature of 600 °C with 2 h. The obtained thin films by spin coater method have a film thickness in the order of 400 nm. The prepared Cu doped NiO thin films have a polycrystalline with cubic structure (200) peak was observed. The optical property shows that the prepared thin films have a transmittance of about 70 %. The Cu doped NiO thin films have minimum bandgap energy is 3.85 eV at 12.9 at.%, the thin film deposited at 8.6 at.% has the highest value of Urbach energy is 425 meV. The Cu doped NiO thin films have a high electrical conductivity of 8.6 at% it is 7 (Ω.cm)−1. The prepared Cu doped NiO thin film was suitable for gas sensing applications due to the existing phase and higher electrical conductivity.

Abstract

In the purpose of exploring new Heusler alloys with different magnetic applications, we have employed first principles calculations method within density functional theory. After checking the structural stability of X2YZ Heusler alloys (X = Fe, Co; Y =Zr, Mo and Z = Ge, Sb), we found that Cu2MnAl type structure is more favorable for most compounds except for X2MoGe and Co2MoSb, were the Hg2CuTi structure is energetically more stable. The trends in magnetic and electronic structures can be predicted by the structure types as well as the different kinds of hybridizations between the constituents. Among the two series only two compounds were identified to be true half metals with potential applications in spintronic devices. While one compound was classified as a nonmagnetic semiconductor with a small band gap. For the rest of materials, we found that the metallic behavior is dominant. These materials show possible interesting features in technical applications as well. The effect of distortion on the magnetic properties of Co2ZrGe and Fe2ZrSb showed that the half metallic character was preserved within a moderate range of volume changes, which makes it possible to grow these materials as thin films with modern techniques.