Fujian Provincial Key Subject of Condensed Matter Physics

*Corresponding author: Prof. Zhigao Huang (zghuang@fjnu.edu.cn)

First-principles study of the stability, vibrational and magnetic properties in hydrogen related Co doped ZnO

Jianmin Zhang, Qingyun Wu, Zhigao Chen, Zhigao Huang∗Department of Physics, Fujian Normal University, Fuzhou 350007, People’s Republic of China

Methods and model

Introduction

Acknowledgments

Results Conclusions

IEEE Magnetics Society Summer School, 2009

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0.50000.75000.7500

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Zn

OZn

Co

OH

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4.000

Sites △ E (eV) dO-H (Å) ω0(cm-1) △ ω(cm-1) ω(cm-1)

BC⊥ 0.00 0.997 3774 -271 3503

BC∥ 0.20 1.006 3720 -258 3462

OA⊥ 0.34 0.990

OA∥ 0.35 0.991

AB’O,∥ 0.41 0.992

ABO,⊥ 0.42 0.990

ABO,∥ 0.45 0.990

All the calculations using Vienna ab-initio Simulation Package (VASP) based on density functional theory (DFT). Projector augmented wave (PAW) method and generalized gradient approximation (GGA) in PBE scheme. Plane wave cutoff energy: 520 eV. k-points grid for Brillouin Zone integration: 3×3×2 (Γcenter). Relaxed until the force less than 0.02 eV/Ǻ.

Fig.1 The 3 × 3 × 2 supercell of wurtzite ZnO containing 36 Zn(gray) and 36 O(red) atoms with one Zn substituted by a Co(green). One H(blue) was introduced at the BC⊥ interstitial site. All the atoms were labeled from 1 to 73.

Fig.2 Possible hydrogen sites in the (11-20) plane of wurtzite ZnO.

Diluted magnetic semiconductors (DMSs), especially ZnO based DMSs, are thought to be ideal materials for spintronics applications. Room-temperature ferromagnetism (RTFM) was observed in Co-doped ZnO. Hydrogen exists in the prepared process for growth of ZnO, such as MOCVD, HVPE, MBE. Theoretical calculations suggested that hydrogen can readily incorporate as H+ (a shallow donor) in ZnO, leading to the cause of the unintentional n-type conductivity. Recent studies indicated that H-impurity was suggested to induce high-temperature FM in ZnO:Co. Vibrational spectroscopy, which measures frequencies of the local vibrational modes (LVMs) of the hydrogen-related configurations, holds the key to reveal the interaction of hydrogen with its neighbors. The origin of ferromagnetism in Co-doped ZnO material is still controversial. Accordingly, we study the stability and vibrational frequences of hydrogen embedded ZnO:Co. Then we discuss the magnetic properties before and after hydrogen was introduced.

Fig.1Fig.2

Fig.3 Charge density for H at most stable site (BC⊥) Fig.4 The electron transfer structures for (a) ZnCoO and pure ZnO (b) ZnCoO with H+ at BC ⊥ site and pure ZnO. Interstitial H embed into Co-O bond and incorporate strongly with O.Hydrogen induce Co and its neighbor O atoms to transfer more electron.

Fig.3

Fig.4

Supported by NSF of China (No. 60876069 ), National Key Project for Basic Research of China (No. 2005CB623605), Fund of National Engineering Research Center for Optoelectronic Crystalline Materials (2005DC105003).

Table.1 BC ⊥ (Bond Center) site was most stable for H between different candidates. Vibrational frequences ω were given including the harmonic frequency ω0 and anharmonic frequency Δω.

Total density of states (DOS) and projected density of states (PDOS) of ZnCoO (Fig.5) and ZnCoO with H+ at BC⊥ site (Fig.6). Coupling between Co-3d and O-2p electrons results in a hybridization at fermi level for ZnCoO, this system is half-metallic with 100% spin polarization. H induces the hybridization causing by Co and O at the fermi level.

Fig.5 Fig.6

H is most stable at BC⊥ of Co–O site, bonding strongly with oxygen. Vibrational frequences of O-H bond for H at BC site are calculated (Table. 1) H mediates the coupling of its neighbor atoms and changes the magnetism and DOS structure of Co-doped ZnO.