Search results for "Materials Science | Hot Paper"
showing 10 items of 1457 documents
Epitaxy of thin films of the Heusler compound Co2Cr0.6Fe0.4Al
2006
Epitaxial thin films of the highly spin polarized Heusler compound Co2Cr0.6Fe0.4Al are deposited by dc magnetron sputtering. It is shown by XRD and TEM investigations how the use of an Fe buffer layer on MgO(100) substrates supports the growth of highly ordered Co2Cr0.6Fe0.4Al at low deposition temperatures. The as grown samples show a relatively large ordered magnetic moment of mu = 3.0mu_B/f.u. providing evidence for a low level of disorder.
Intrinsic and extrinsic anomalous transport properties of Heusler ferromagnets Fe$_2$CoAl and Fe$_2$NiAl from first principles
2023
Recently, Heusler ferromagnets have been found to exhibit unconventional anomalous electric, thermal, and thermoelectric transport properties. In this study, we employed first-principles density functional theory calculations to systematically investigate both intrinsic and extrinsic contributions to the anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and anomalous thermal Hall effect (ATHE) in two Heusler ferromagnets: Fe$_2$CoAl and Fe$_2$NiAl. Our analysis reveals that the extrinsic mechanism originating from disorder dominates the AHE and ATHE in Fe$_2$CoAl , primarily due to the steep band dispersions across the Fermi energy and corresponding high longitudinal electronic co…
Prediction of giant mechanocaloric effects in fluorite-structured superionic materials
2016
Mechanocaloric materials experience a change in temperature when a mechanical stress is adiabatically applied on them. Thus far, only ferroelectrics and superelastic metallic alloys have been considered as potential mechanocaloric compounds to be exploited in solid-state cooling applications. Here we show that giant mechanocaloric effects occur in hitherto overlooked fast ion conductors (FIC), a class of multicomponent materials in which above a critical temperature, Ts, a constituent ionic species undergoes a sudden increase in mobility. Using first-principles and molecular dynamics simulations, we found that the superionic transition in fluorite-structured FIC, which is characterised by a…
Giant magnetoresistance and extraordinary magnetoresistance in inhomogeneous semiconducting DyNiBi
2007
The semiconducting half-Heulser compound DyNiBi shows a negative giant magnetoresistance (GMR) below 200 K. Except for a weak deviation, this magnetoresistance scales roughly with the square of the magnetization in the paramagnetic state, and is related to the metal-insulator transition. At low temperature, a positive magnetoresistance is found, which can be suppressed by high fields. The magnitude of the positive magnetoresistance changes slightly with the amount of impurity phase.
Alternative Buffer-Layers for the Growth of SrBi2Ta2O9 on Silicon
2000
In this work we investigate the influence of the use of YSZ and CeO2/YSZ as insulators for Metal- Ferroelectric-Insulator-Semiconductor (MFIS) structures made with SrBi2Ta2O9 (SBT). We show that by using YSZ only the a-axis oriented Pyrochlore phase could be obtained. On the other hand the use of a CeO2/YSZ double-buffer layer gave a c-axis oriented SBT with no amorphous SiO2 inter- diffusion layer. The characteristics of MFIS diodes were greatly improved by the use of the double buffer. Using the same deposition conditions the memory window could be increased from 0.3 V to 0.9 V. From the piezoelectric response, nano-meter scale ferroelectric domains could be clearly identified in SBT thin…
Reliable magnetic domain wall propagation in cross structures for advanced multi-turn sensor devices
2017
We develop and analyze an advanced concept for domain wall based sensing of rotations. Moving domain walls in n closed loops with n-1 intersecting convolutions by rotating fields, we can sense n rotations. By combining loops with coprime numbers of rotations, we create a sensor system allowing for the total counting of millions of turns of a rotating applied magnetic field. We analyze the operation of the sensor and identify the intersecting cross structures as the critical component for reliable operation. In particular depending on the orientation of the applied field angle with the magnetization in the branches of the cross, a domain wall is found to propagate in an unwanted direction yi…
Structural, vibrational, and electronic properties of TlReO4 studied using a first principles approach
2019
Present work provides extensive DFT study of TlReO4 using pseudopotential approach for understanding the structural and vibrational properties and full-potential linearized augmented plane wave method for electronic band structure and associated optical properties. Calculated bulk modulus value 29.77 GPa using LDA functional is found to be close to experimental value 26 GPa. The order of elastic constant along the principal axis clearly indicates the crucial role of Re and O3 atoms in the structural and mechanical properties of this material. Analysis of Born effective charge (BEC) along with gamma point phonon frequencies through density functional perturbation approach (DFPT) have also sh…
Macroscopic description of the two-dimensional LaAlO$_3$/SrTiO$_3$ interface
2015
We propose a simple analytical model to explain possible appearance of the metallic conductivity in the two-dimensional (2D) LaAlO$_3$/SrTiO$_3$ interface. Our model considers the interface within a macroscopic approach which is usual to semiconductor heterojunctions and is based on drift-diffusion equations. The solution of these equations allows to obtain the positions of band edges as a function of distances from the interface. We show that for the 2D metallic conductivity to appear at the interface, the constituting substances should have the same type (either electronic or hole) of conductivity; in the opposite case the possible transition to metallic phase has a three-dimensional char…
Ab initio calculations of the atomic and electronic structures for ABO3 perovskite (001) surfaces
2004
We present the results of first-principles calculations on two possible terminations of the (001) surfaces of SrTiO3 (STO), BaTiO3 (BTO), and PbTiO3 (PTO) perovskite crystals. Atomic structure and the electronic configurations were calculated for different 2D slabs, both stoichiometric and non-stoichiometric, using hybrid (B3PW) exchange-correlation technique and reoptimized basis sets of atomic (Gaussian) orbitals. Results are compared with previous calculations and available experimental data. The electronic density distribution near the surface and covalency effects are discussed in details for all three perovskites.
Challenges in Truncating the Hierarchy of Time-Dependent Reduced Density Matrices Equations: Open Problems
2012
In this work, we analyze the Born, Bogoliubov, Green, Kirkwood and Yvon (BBGKY) hierarchy of equations for describing the full time-evolution of a many-body fermionic system in terms of its reduced density matrices (at all orders). We provide an exhaustive study of the challenges and open problems linked to the truncation of such hierarchy of equations to make them practically applicable. We restrict our analysis to the coupled evolution of the one- and two-body reduced density matrices, where higher order correlation effects are embodied into the approximation used to close the equations. We prove that within this approach, the number of electrons and total energy are conserved, regardless…