Ab initio investigation on the magnetic ordering in Gd doped ZnO

Abstract

The current study investigates the magnetic properties of the GdxZn1-xO, with x=0.0625 and 0.0185, doped semiconductor using the full potential (linearized) augmented plane wave plus local orbital method. We show that in contrast to the findings of Shi et al. [J. Appl. Phys. 106, 023910 (2009)], the implementation of the Hubbard U parameter to the Gd f states favors an antiferromagnetic phase in both wurtzite GdO and GdxZn1-xO. Spin polarized calculations on GdxZn1-xO indicate that, even if a ferromagnetic ground state were favored, the magnetic influence of Gd in a perfect ZnO wurtzite lattice is highly localized and limited to the first three nearest neighboring O atoms. Increasing the supercell size and thus diluting the concentration of Gd within the ZnO matrix does not show any changes in the net magnetic moment between these three O atoms nor in the remaining lattice sites, indicating that sizing effects do not influence the range of matrix polarization. We conclude that the localized Gd induced polarization can not account for long range magnetic ordering in a defect-free ZnO wurtzite lattice.

Defect-band mediated ferromagnetism in Gd-doped ZnO thin films

“…In addition, s-f exchange can be stronger than f-f or f-p exchange. 8,27 One of the concerns here is related to the location of the Fermi level (E F ) and 4f levels in the band, which is required to establish such magnetic exchange. Earlier theoretical studies showed that the 4f levels lie inside the conduction band (CB) (spin-down) and valence (spin-up) bands in Gd:ZnO.…”

Ferromagnetism in Gd doped ZnO nanowires: A first principles study

“…While the same applies to Gd doping, the observed ferromagnetic coupling depends on the crystal structure and positions of the dopant atoms in the host matrix, as well as the distance between RE dopants. 8 FM is observed experimentally in ZnO thin films 9,10 and ZnO nanostructures doped with RE elements, such as Eu, Nd, and Gd. 11,12 In several experiments on ZnO nanowires doped with Gd, huge magnetic moments (3278l B /Gd) were obtained, which is attributed to the exchange interaction between 4f and 6s electrons.…”

“…8 To determine the preferred Gd positions, total energy calculations are performed for 12 configurations, divided into 3 groups, encompassing surface, sub-surface, and bulk-like regions, as shown in Fig. 1 (groups 1, 2, and 3 …”

“…A few theoretical studies have reported weak FM in RE-doped bulk ZnO in zincblende and wurtzite structures. [6][7][8] Even though the 4f levels are localized in RE elements, f electrons can couple strongly with host s electrons, 6 yielding the possibility of carriermediated FM. 7 In particular, the interest in ZnO nanostructures has significantly increased in recent years owing to their unique optical, magnetic, and mechanical properties, leading to many potential applications.…”

“…The few theoretical studies that have been conducted thus far deal with RE doping in bulk ZnO and do not elucidate the mechanisms responsible for RTFM in Gd-doped wurtzite ZnO nanostructures. [6][7][8] On the other hand, it is important to understand the physical mechanisms responsible for the FM in ZnO nanostructures from both fundamental and technological perspectives. In this paper, we demonstrate FM in Gd-doped Zn 48 O 48 nanowires oriented along the wurtzite [0001] direction, as well as the effect of point defects on the magnetic coupling, using first-principles calculations.…”