Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userElectronic correlations in short period (CrAs)$_n$/(GaAs)$_n$ ferromagnetic heterostructures
106
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate half-metallicity in [001] stacked (CrAs)$_n$/(GaAs)$_n$ heterostructures with $n leq 3$ by means of a combined many-body and electronic structure calculation. Interface states in the presence of strong electronic correlations are discussed for the case $n=1$. For $n=2,3$ our results indicate that the minority spin half-metallic gap is suppressed by local correlations at finite temperatures, and continuously shrinks upon increasing the heterostructure period. Although around room temperature the magnetization of the heterostructure deviates by only $2%$ from the ideal integer value, finite temperature polarization at $E_F$ is reduced by at least $25%$. Below the Fermi level the minority spin highest valence states are found to localize more on the GaAs layers while lowest conduction states have a many-body origin. Our results, therefore, suggest that in these heterostructures holes and electrons remain separated among different layers.
rate research
Read More
The effects of local electronic interactions and finite temperatures upon the transmission across the Cu$_4$CoCu$_4$ metallic heterostructure are studied in a combined density functional and dynamical mean field theory. It is shown that, as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant $d$-electrons contribution, as compared to the non-correlated case in which the transport is dominated by $s$ and $p$ electrons.
At interfaces between oxide materials, lattice and electronic reconstructions always play important roles in exotic phenomena. In this study, the density functional theory and maximally localized Wannier functions are employed to investigate the (LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ magnetic superlattices. The electron transfer from Ti$^{3+}$ to V$^{3+}$ is predicted, which violates the intuitive band alignment based on the electronic structures of LaTiO$_3$ and LaVO$_3$. Such unconventional charge transfer quenches the magnetism of LaTiO$_3$ layer mostly and leads to metal-insulator transition in the $n=1$ superlattice when the stacking orientation is altered. In addition, the compatibility among the polar structure, ferrimagnetism, and metallicity is predicted in the $n=2$ superlattice.
Magnetocaloric effect in {[Fe(pyrazole)$_4$]$_2$[Nb(CN)$_8$]$cdot$4H$_2$O}$_n$ molecular magnet is reported. It crystallizes in tetragonal I4$_1$/a space group. The compound exhibits a phase transition to a long range magnetically ordered state at $T_mathrm{c}approx$8.3 K. The magnetic entropy change $Delta S_mathrm{M}$ as well as the adiabatic temperature change $Delta T_mathrm{ad}$ due to applied field change $mu_0Delta H$=0.1, 0.2, 0.5, 1, 2, 5, 9 T as a function of temperature have been determined by the relaxation calorimetry measurements. The maximum value of $Delta S_mathrm{M}$ for $mu_0Delta H=5$ T is 4.9 J mol$^{-1}$ K$^{-1}$ (4.8 J kg$^{-1}$ K$^{-1}$) at 10.3 K. The corresponding maximum value of $Delta T_mathrm{ad}$ is 2.0 K at 8.9 K. The temperature dependence of the exponent $n$ characterizing the field dependence of $Delta S_mathrm{M}$ has been estimated. It attains the value of 0.64 at the transition temperature, which is consistent with the 3D Heisenberg universality class.
The electronic structure of bulk fcc GaAs, fcc and tetragonal CrAs, and CrAs/GaAs supercells, computed within LMTO local spin-density functional theory, is used to extract the band alignment (band offset) for the [1,0,0] GaAs/CrAs interface in dependence of the spin orientation. With the lateral lattice constant fixed to the experimental bulk GaAs value, a local energy minimum is found for a tetragonal CrAs unit cell with a slightly ($approx$ 2%) reduced longitudinal ([1,0,0]) lattice constant. Due to the identified spin-dependent band alignment, half-metallicity of CrAs no longer is a key requirement for spin-filtering. Encouraged by these findings, we study the spin-dependent tunneling current in [1,0,0] GaAs/CrAs/GaAs heterostructures within the non-equilibrium Greens function approach for an effective tight-binding Hamiltonian derived from the LMTO electronic structure. Results indicate that these heterostructures are probable candidates for efficient room-temperature all-semiconductor spin-filtering devices.
The electronic structures of substitutional rare-earth (RE) impurities in GaAs and cubic GaN are calculated. The total energy is evaluated with the self-interaction corrected local spin density approximation, by which several configurations of the open 4f shell of the rare-earth ion may be investigated. The defects are modelled by supercells of type REGa$_{n-1}$As$_n$, for n=4, 8 and 16. The preferred defect is the rare-earth substituting Ga, for which case the rare-earth valency in intrinsic material is found to be trivalent in all cases except Ce and Pr in GaN. The 3+ --> 2+ f-level is found above the theoretical conduction band edge in all cases and within the experimental gap only for Eu, Tm and Yb in GaAs and for Eu in GaN. The exchange interaction of the rare-earth impurity with the states at both the valence band maximum and the conduction band minimum is weak, one to two orders of magnitude smaller than that of Mn impurities. Hence the coupling strength is insufficient to allow for ferromagnetic ordering of dilute impurities, except at very low temperatures.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
