Yiren Wang

Electronic and magnetic properties of Co doped MoS2 monolayer.

First principle calculations are employed to calculate the electronic and magnetic properties of Co doped MoS2 by considering a variety of defects including all the possible defect complexes. The results indicate that pristine MoS2 is nonmagnetic. The materials with the existence of S vacancy or Mo vacancy alone are non-magnetic either. Further calculation demonstrates that Co substitution at Mo site leads to spin polarized state. Two substitutional CoMo defects tend to cluster and result in the non-magnetic behaviour. However, the existence of Mo vacancies leads to uniform distribution of Co dopants and it is energy favourable with ferromagnetic coupling, resulting in an intrinsic diluted magnetic semiconductor.

Zn vacancy induced ferromagnetism in K doped ZnO

Using first-principle calculations, we studied the mechanism of the magnetic properties of K doped ZnO. The results show that the magnetic moment originates from the O 2p hole states around Zn vacancies. K substitution in Zn can also induce magnetism, which is due to the formation of the partial Zn vacancy induced by lattice distortion. Ferromagnetic ordering occurs via p–p coupling, which is mediated by the holes that result from K doping. Further investigation indicates that a single Zn vacancy has a high formation energy, whereas the formation energy of a defect complex composed of K interstitial (Kint), K substitutional (KZn) and zinc vacancy (VZn) is significantly reduced. In addition, K dopants prefer a large separation, which suggests uniform distribution. Experimentally, K doped ZnO nanorods were fabricated using a hydrothermal method and room temperature ferromagnetism was observed. 2 at% K doped ZnO has the largest saturation magnetization, which is consistent with first-principle calculations.

Magnetic properties in α-MnO2 doped with alkaline elements

α-MnO2 nanotubes were fabricated using a hydrothermal technique. Li, Na and K ions were introduced into MnO2 nanotubes to tailor their magnetic properties. It was found that with a doping concentration lower than 12 at%, the nanotubes showed ferromagnetic-like ordering at low temperature (<50u2005K), while antiferromagnetic coupling dominated their physical behavior with doping concentrations beyond 12 at%. Such experimental phenomenon was in very good agreement with associated first principle calculations. The ferromagnetic-like ordering originates from the breaking of equivalence between two different Mn-O octahedrals in α-MnO2 due to the filling of alkaline ions in the tunnels. Both small charge transfer and lattice distortion play important roles in the ferromagnetic ordering.

Intrinsic or interface clustering induced ferromagnetism in Fe-doped In2O3 diluted magnetic semiconductors

Five percent Fe-doped In2O3 films were deposited using a pulsed laser deposition system. X-ray diffraction and transmission electron microscopy analysis show that the films deposited under oxygen partial pressures of 10-3 and 10-5 Torr are uniform without clusters or secondary phases. However, the film deposited under 10-7 Torr has a Fe-rich phase at the interface. Magnetic measurements demonstrate that the magnetization of the films increases with decreasing oxygen partial pressure. Muon spin relaxation (μSR) analysis indicates that the volume fractions of the ferromagnetic phases in PO2 = 10-3, 10-5, and 10-7 Torr-deposited samples are 23, 49, and 68%, respectively, suggesting that clusters or secondary phases may not be the origin of the ferromagnetism and that the ferromagnetism is not carrier-mediated. We propose that the formation of magnetic bound polarons is the origin of the ferromagnetism. In addition, both μSR and polarized neutron scattering demonstrate that the Fe-rich phase at the interface has a lower magnetization compared to the uniformly distributed phases.