Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userElectronic and magnetic properties of the (001) surface of hole-doped manganites
108
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The electronic and magnetic properties of ferromagnetic doped manganites are investigated by means of model tight-binding and textit{ab initio} self-interaction corrected local spin density approximation calculations. It is found that the surface alone by breaking the cubic symmetry induces a difference in the occupation of the two $e_{g}$ orbitals at the surface. With textit{ab initio} calculations we found surface localisation of one orbital and hence a change in the Mn valency from four in the bulk to three at the sub-surface. Different surface or disordered interface induced localisation of the orbitals are considered too with respect to the nature and the strength of the magnetic exchange coupling between the surface/interface and the bulk-like region.
rate research
Read More
The complicated electronic, magnetic, and colossal magnetoresistant (CMR) properties of Sr and Ca doped lanthanum manganites can be understood by spin-polarized first-principles calculations. The electronic properties can be attributed to a detailed balancing between Sr and Ca induced metal-like O 2p and majority-spin (majority-spin) Mn eg delocalized states and the insulator-like minority-spin (minority-spin) Mn t2g band near the Fermi level (EF). The magnetic properties can be attributed to a detailed balancing between O mediated antiferromagnetic superexchange and delocalized majority-spin Mn eg-state mediated ferromagnetic spin-spin couplings. While CMR can be attributed to the lining up of magnetic domains trigged by the applied magnetic field, which suppresses the trapping ability of the empty Mn t2g states that resists the motion of conducting Mn majority-spin eg electrons.
We have succeeded in preparing high-quality Gd-doped single-crystalline EuO films. Using Eu-distillation-assisted molecular beam epitaxy and a systematic variation in the Gd and oxygen deposition rates, we have been able to observe sustained layer-by-layer epitaxial growth on yttria-stabilized cubic zirconia (001). The presence of Gd helps to stabilize the layer-by-layer growth mode. We used soft x-ray absorption spectroscopy at the Eu and Gd M4,5 edges to confirm the absence of Eu3+ contaminants and to determine the actual Gd concentration. The distillation process ensures the absence of oxygen vacancies in the films. From magnetization measurements we found the Curie temperature to increase smoothly as a function of doping from 70 K up to a maximum of 125 K. A threshold behavior was not observed for concentrations as low as 0.2%.
Despite its potential in the fields of optoelectronics and topological insulators, experimental electronic band structure studies of Bi-doped GaAs are scarce. The reason is the complexity of growth which tends to leave bulk and in particular surface properties in an undefined state. Here we present an in depth investigation of structural and electronic properties of GaAsBi epilayers grown by molecular beam epitaxy with high (001) crystalline order and well-defined surface structures evident from low-energy electron diffraction. X-ray and ultraviolet photoemission spectrocopy as well as angle-resolved photoemission data at variable photon energies allows to disentangle a Bi-rich surface layer with $(1times3)$ symmetry from the effects of Bi atoms incorporated in the GaAs bulk matrix. The influence of Bi concentrations up to $approx 1$% integrated in the GaAs bulk are visible in angle-resolved photoemission spectra after mild ion bombardment and subsequent annealing steps. Interpretation of our results is obtained via density functional theory simulations of bulk and $beta 2(2times 4)$ reconstructed slab geometries with and without Bi. Bi-induced energy shifts in the dispersion of GaAs heavy and light hole bulk bands are evident both in experiment and theory, which are relevant for modulations in the optical band gap and thus optoelectronic applications.
Although La(2)Cu(1-x)Li(x)O(4) [Li-LCO] differs from La(2-x)Sr(x)CuO(4) [Sr-LCO] in many ways (e.g., the absence of metallic transport, high-Tc superconductivity, and incommensurate antiferromagnetic correlations), it has been known that certain magnetic properties are remarkably similar. The present work establishes the detailed bulk magnetic phase diagram of Li-LCO (0 <= x <= 0.07), which is found to be nearly identical to that of lightly-doped Sr-LCO, and therefore extends the universality of the phase diagram to hole-doped but nonsuperconducting cuprates.
We have studied NpPdSn by means of the heat capacity, electrical resistivity, Seebeck and Hall effect, $^{237}$Np M{o}ssbauer spectroscopy, and neutron diffraction measurements in the temperature range 2-300 K and under magnetic fields up to 14 T. NpPdSn orders antiferromagnetically below the Neel temperature $T_N$ = 19 K and shows localized magnetism of Np$^{3+}$ ion with a a doubly degenerate ground state. In the magnetic state the electrical resistivity and heat capacity are characterized by electron-magnon scattering with spin-waves spectrum typical of anisotropic antiferromagnets. An enhanced Sommerfeld coefficient and typical behavior of magnetorestistivity, Seebeck and Hall coefficients are all characteristic of systems with strong electronic correlations. The low temperature antiferromagnetic state of NpPdSn is verified by neutron diffraction and $^{237}$Np M{o}ssbauer spectroscopy and possible magnetic structures are discussed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
