Ferromagnetism in Gd doped ZnO nanowires: A first principles study

Abstract

Size effects on formation energies and electronic structures of oxygen and zinc vacancies in ZnO nanowires: A first-principles study J. Appl. Phys. 109, 044306 (2011) In several experimental studies, room temperature ferromagnetism in Gd-doped ZnO nanostructures has been achieved. However, the mechanism and the origin of the ferromagnetism remain controversial. We investigate the structural, magnetic, and electronic properties of Zn 48 O 48 nanowires doped with Gd, using density functional theory. Our findings indicate that substitutionally incorporated Gd atoms prefer occupying the surface Zn sites. Moreover, the formation energy increases with the distance between Gd atoms, signifying that no Gd-Gd segregation occurs in the nanowires within the concentration limit of 2%. Gd induces ferromagnetism in ZnO nanowires with magnetic coupling energy up to 21 meV in the neutral state, which increases with additional electron and O vacancy, revealing the role of carriers in magnetic exchange. The potential for achieving room temperature ferromagnetism and high T C in ZnO:Gd nanowires is evident from the large ferromagnetic coupling energy (200 meV

Magnetic Properties of Gadolinium-Doped ZnO Films and Nanostructures

“…The introduction of additional charge to the nanowire by the injection of an electron further enhanced ΔE, indicating that the presence of O vacancies may stabilize ferromagnetic coupling in the nanowire, given that a single O vacancy can release two electrons into the system. The ΔE increased to 200 meV in the presence of O vacancies, supporting the possibility of an increased f-s coupling ( Table 1 [ 53]). The density of states (DOS) of Gd-doped ZnO nanowires with and without O vacancies provided further insight into the exchange mechanism.…”

“…The density of states (DOS) of Gd-doped ZnO nanowires with and without O vacancies provided further insight into the exchange mechanism. A pristine ZnO nanowire is semiconducting with nonmagnetic characteristics (Figure 15) [53]. Doping with Gd atom causes a significant shift of the Fermi level to the conduction band close to the Gd f states.…”

“…The presence of point defects in the nanowire along with the Gd dopant is discussed in the context of magnetic and electronic properties. The possibility of carrier-mediated ferromagnetism originating from the f-s coupling was demonstrated using electronic structure analysis [53].…”

“…Gd nanowires with all 12 non-equivalent doping sites grouped in to three classes including the surface, subsurface, and bulk-like sites. The formation energy of Gd atoms in each site is also shown (in eV) [53].…”

Defect induced d ferromagnetism in a ZnO grain boundary

“…Hole injection enhances the hybridization of states near VB by moving the E F towards the VBM, thus, enhancing the magnetic coupling. 38 On the other hand, increasing electron carrier density is expected to move the E F away from the VBM, into the conduction band, 39 reducing the hybridization near the E F whereby no ferromagnetic enhancement can take place. We find that weak ferromagnetic coupling is favored for the neutral charge state for both configurations, with small energy differences (∆E < 30 meV).…”