arXiv subjects

Wenxu Zhang

Publications and source records attributed to Wenxu Zhang.

22 records · Page 2Linked to original sources

arXiv2012

Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation

The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ions implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is 3d6 configuration, the same as in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system.

cond-mat.mtrl-sci↗

arXiv2012

Tune of Magnetism and Electronic Structures of Alkali Metal Carbides with Rocksalt Structure

Electronic structures of carbides with the rocksalt structure were calculated by full potential electronic codes solving the Kohn-Sham equation. Bonding characters were analyzed by constructing tight-binding Hamiltonian based on maximally-localized Wannier functions. It was found that the cations in these compounds act as an electron provider and the frame is formed by the carbon atoms. The electronic states in the vicinity of the Fermi level are mainly from the p-orbitals of C. Pressure and doping are two efficient ways to tune the magnetic and electronic properties of these compounds. It turns out that a spin gapless semiconductor can be obtained by applying hydrostatic pressure up to tens of gigaPascal. Higher pressure induced an insulator to metal transition because of band broadening. Compounds of IA group (Na, K, Rb, Cs) were magnetic semiconductor at ambient conditions. Alloying with IIA elements decrease the magnetic moment according to the law of $3-x$, where $x$ is the relative atomic ratio of the IIA elements to the IA ones. The behaviors of the compounds under the pressure and the doping effects can be understood by a rigid band model.

cond-mat.mtrl-sci↗

arXiv2012

Electronic structure and magnetism in M(=IA, IIA)C compounds with the rocksalt structure

Electronic structures of MC where M is the alkali and alkaline earth metals with the rocksalt structure are calculated by full potential density functional codes. We find that the spin magnetic moment in the compounds is mainly contributed by the spin polarized p-orbitals of carbon. The large distance between the carbon makes the p-orbitals localized, which induces magnetic instability according to the Stoner criterion. The electronic structure can be mapped to the rigid band model. SrC, BaC and RaC are half-metals, while KC, RbC and CsC are magnetic semiconductors

cond-mat.mtrl-sci↗

arXiv2012

Comment on "First-principles studies on magnetic properties of rocksalt structure $M$C ($M$=Ca,Sr, and Ba) under pressure"[Appl. Phys. Lett. 98,182501(2011)]

In this comment on 'First-principles studies on magnetic properties of rocksalt structure MC(M=Ca, Sr, and Ba) under pressure'[Appl. Phys. Lett. 98, 182501 (2011)]" we found that their results of the original paper are from nonconverged calculation with respect to the k-point mesh, because they used too few k-points. This gives meaningless results presented in Fig. 1, 2 and 3 in the paper. We recalculated the correpsonding curves.

cond-mat.mtrl-sci↗