Abstract
The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.
Highlights
As a practical example of this new general approach, we focus here on a detailed experimental and theoretical study of the heavy atom dopant, bismuth, which has an explicit impact on the electronic states of p-symmetry in the semiconductor matrix and the mediation of the ferromagnetic interactions
In this work we present experimental and theoretical evidence of room temperature ferromagnetism of Bi doped ZnO and we explore its microscopic origin in this system
We calculate the X-ray Magnetic Circular Dichroism (XMCD) of a volume expanded ZnO lattice by 7% to model the film surface region probed by Total Electron Yeild (TEY) and the bulk ZnO structure, a contribution to the signal which should be present in the Total Fluorescence Yield (TFY) results
Summary
The formation energy of the ZnBixO1−x with respect to the bulk and isolated Bi atom is given in. To study the magnetic properties of this compound, Bi atoms are placed in two oxygen sites in the supercell, for different doping concentrations. The estimated formation energies of the system are 0.06 and 0.11 eV per formula unit at the doping level of 1.56% and 3.12% respectively, versus bulk ZnO and an isolated Bi atom. In the case of ZnBixO1−x with a doping concentration 3.12%, our calculations show that the system is ferromagnetically stable with the energy difference of 108.5 meV (Table 1).
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