Electronic structure and magnetic properties of Mn and Fe impurities near the GaAs (110) surface

Combining density functional theory calculations and microscopic tight-binding models, we investigate theoretically the electronic and magnetic properties of individual substitutional transition-metal impurities (Mn and Fe) positioned in the vicinity of the (110) surface of GaAs. For the case of the [Mn2+]0 plus acceptor-hole (h) complex, the results of a tight-binding model including explicitly the impurity delectrons are in good agreement with approaches that treat the spin of the impurity as an effective classical vector. For the case of Fe, where both the neutral isoelectronic [Fe3+]0 and the ionized [Fe2+]− states are relevant to address scanning tunneling microscopy (STM) experiments, the inclusion of d orbitals is essential. We find that the in-gap electronic structure of Fe impurities is significantly modified by surface effects. For the neutral acceptor state [Fe2+,h]0, the magnetic-anisotropy dependence on the impurity sublayer resembles the case of [Mn2+,h]0. In contrast, for [Fe3+]0 electronic configuration the magnetic anisotropy behaves differently and it is considerably smaller. For this state we predict that it is possible to manipulate the Fe moment, e.g., by an external magnetic field, with detectable consequences in the local density of states probed by STM

CORRELATION OF ALKALOID CONTENT AND TASTE OF HONEY FROM VARIOUS PROVINCES IN INDONESIA

Objective: This study analyzed the correlation between alkaloid contents and taste (bitter and rough taste). Methods: Qualitative analysis was analyzed using Mayer and Draggendorff methods, while quantitative analysis was analyzed using spectrophotometric methods. Taste evaluation in each sample was carried out by descriptive method with parameters including bitter and rough taste. The correlation between alkaloid content and taste in honey was statistically analyzed using a correlation test. Results: The alkaloids testing showed that the sample with the highest alkaloid content was Tetragonula fuscobalteata honey from Sumbawa province, with an alkaloid content of 119.71 mg/g. In contrast, the sample with the lowest alkaloid content was Geniotrigona thoracica from West Sumatra at 21.24 mg/g. Taste evaluation results showed that the sample with the highest alkaloid content had the most bitter and rough taste. Conclusion: Honey that has the highest alkaloid content is T. fuscobalteata Sumbawa, with an alkaloid content of 119.71 mg/g, because the availability of adequate alkaloid feed supports this species. In contrast, the honey with the lowest alkaloid content was G. thorasica, with an alkaloid content of 21.24 mg/g, because the availability of adequate alkaloid feed did not support this species. Based on the data, the alkaloid content of honey has a linear correlation with the bitter and rough taste. The higher alkaloid content in honey causes the honey taste to become more bitter and rough

Magnetic Anisotropy of Single Mn Acceptors in GaAs in an External Magnetic Field

We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Crosssectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wavefunction is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tightbinding model of Mn acceptors in GaAs. For Mn acceptors on the (110) surface and the subsurfaces immediately underneath, we find that an applied magnetic field modifies significantly the magnetic anisotropy landscape. However the acceptor hole wavefunction is strongly localized around the Mn and the LDOS is quite independent of the direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed on deeper layers below the surface, the acceptor hole wavefunction is more delocalized and the corresponding LDOS is much more sensitive on the direction of the Mn magnetic moment. However the magnetic anisotropy energy for these magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can hardly change the landscape and rotate the direction of the Mn magnetic moment away from its easy axis. We predict that substantially larger magnetic fields are required to observe a significant field-dependence of the tunneling current for impurities located several layers below the GaAs surface.Comment: Non