arXiv subjects

Olof Karis

Publications and source records attributed to Olof Karis.

21 records · Page 2Linked to original sources

arXiv2011

Atomic scale chemical fluctuation in LaSrVMoO6: A proposed halfmetallic antiferromagnet

Half metallic antiferromagnets (HMAFM) have been proposed theoretically long ago but have not been realized experimentally yet. Recently, a double perovskite compound, LaSrVMoO6, has been claimed to be an almost real HMAFM system. Here, we report detailed experimental and theoretical studies on this compound. Our results reveal that the compound is neither a half metal nor an ordered antiferromagnet. Most importantly, an unusual chemical fluctuation is observed locally, which finally accounts for all the electronic and magnetic properties of this compound.

cond-mat.mtrl-sci↗

arXiv2010

Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films

We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants the enhancement of the magnetic moment at saturation is significant. X-ray magnetic circular dichroism results show a behavior of the spin- and orbital-moment which is consistent with a structural transition at $T_c$. In particular, we find that the ratio of the orbital to spin moment shows a marked increase in the coexistence region of the ferromagnetic $α$- and paramagnetic $β$-phases, a result that is well in accord with the observed increase of the $c/a$-ratio in the same temperature region. The \textit{ab initio} density functional calculations reveal that the magnetic properties are more sensitive towards change in in-plane axis as compared to a change of the out-of-plane axis, which is explained by the analysis of band structures. The effects of electron correlation in MnAs using \textit{ab initio} dynamical mean field theory are also presented.

cond-mat.mtrl-sci↗

arXiv2009

Conductivity engineering of graphene by defect formation

Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behavior around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.

cond-mat.mtrl-sci↗