Tuning magnetism by biaxial strain in native ZnO

Abstract

Magnetic ZnO, one of the most important diluted magnetic semiconductors (DMS), has attracted great scientific interest because of its possible technological applications in optomagnetic devices. Magnetism in this material is usually delicately tuned by the doping level, dislocations, and local structures. The rational control of magnetism in ZnO is a highly attractive approach for practical applications. Here, the tuning effect of biaxial strain on the d(0) magnetism of native imperfect ZnO is demonstrated through first-principles calculations. Our calculation results show that strain conditions have little effect on the defect formation energy of Zn and O vacancies in ZnO, but they do affect the magnetism significantly. For a cation vacancy, increasing the compressive strain will obviously decrease its magnetic moment, while tensile strain cannot change the moment, which remains constant at 2 μB. For a singly charged anion vacancy, however, the dependence of the magnetic moment on strain is opposite to that of the Zn vacancy. Furthermore, the ferromagnetic state is always present, irrespective of the strain type, for ZnO with two zinc vacancies, 2VZns. A large tensile strain is favorable for improving the Curie temperature and realizing room temperature ferromagnetism for ZnO-based native semiconductors. For ZnO with two singly charged oxygen vacancies, 2Vs, no ferromagnetic ordering can be observed. Our work points the way to the rational design of materials beyond ZnO with novel non-intrinsic functionality by simply tuning the strain in a thin film form.

Halide‐Modulated Functionality of Wide Band Gap Zinc Oxide Semiconductor Nanoparticle

“…Based on previous results it is found that, ZnO NP may have very nominal magnetic moment which arises due to the intrinsic defects like surface OV . As discussed in the earlier section, the calculated small magnetic moment obtained for ZnO NP is seen to increase for halide attached NP due to increased electron affinity of attached halide ions and the resulting p‐d hybridization . Experimentally obtained per ion magnetic moments matches closely to the theoretical values as can be seen from Table .…”

“…Subsequently, in ZnO, ferromagnetic ordering has been found to exist in both undoped ZnO NP and also doped with magnetic and non‐magnetic ions. Based on previous results it is found that, ZnO NP may have very nominal magnetic moment which arises due to the intrinsic defects like surface OV . As discussed in the earlier section, the calculated small magnetic moment obtained for ZnO NP is seen to increase for halide attached NP due to increased electron affinity of attached halide ions and the resulting p‐d hybridization .…”

Effect of Strain and Surface Proximity on the Acceptor Grouping in ZnO

“…In particular, the changes in E form are about 0.12 and 0.34 eV in the case of 4% compressive strain, for V Zn and ( V Zn H), respectively. Similar variations in the formation energy for V Zn were observed in refs and . In particular, ref demonstrated for the first time that E form of zinc vacancy does not depend linearly on the strain due to the large structural relaxation around the vacancy.…”

Massive Vacancy Concentration Yields Strong Room-Temperature Ferromagnetism in Two-Dimensional ZnO

“…Ferromagnetism in undoped ZnO has been shown to originate from Zn vacancies (V Zn ) both from experiments ,,− and DFT studies, ,,− however we find that in order to explain the ferromagnetism measured in our experiments, a large concentration of vacancies would be required. Assuming that the ferromagnetism in ZnO originates from V Zn , each V Zn in the bulk is expected to contribute 2 μ B to the total magnetization based on our present DFT calculations (see Supporting Information for more details).…”

“…Point defects, such as vacancies or interstitials, are an essential factor that determine the physical properties of materials. , The ability to control and manipulate point defects in materials synthesis and processing has been a fundamental strategy to achieve numerous desired optical, electrical, and magnetic functionalities . Nevertheless, the concentration of defects are usually restricted to relatively low levels by thermodynamics (e.g., due to high formation energy) or kinetics (e.g., due to slow growth rates). , Irregular defect types or high defect concentrations, though often predicted to enable exotic properties, are often associated with metastable states that are far from equilibrium. , For example, room-temperature ferromagnetism, discovered in ZnO due to the zinc vacancy (V Zn )-induced spin polarization of the top of the valence band, − is intriguing for multiproperty coupling. However, the amplitude of ferromagnetism is generally very weak due to the limited V Zn concentration in the material lattice.…”