Elsevier

Ceramics International

Volume 44, Issue 1, January 2018, Pages 71-75
Ceramics International

Ferromagnetic coupling of Fe3+-VO-Fe3+polarons in Fe-doped ZnO

https://doi.org/10.1016/j.ceramint.2017.09.076Get rights and content

Abstract

Room temperature ferromagnetic Fe-doped ZnO with hexagonal wurtzite structure was synthesized by a hydrothermal method under 4 T high pulsed magnetic field. Detailed studies were carried out to survey the effect of magnetic field on morphological, structural and magnetic properties of samples. The results showed that the concentration of oxygen vacancies (VOs) and amount of Fe3+ doping in ZnO were improved due to the high magnetic field processing. It proposed that the inherent exchange interaction is mediated by magnetic ions (Fe3+) through VOs assist to produce bound magnetic polorans (BMPs), which is responsible for RTFM in Fe-doped ZnO matrix.

Introduction

Diluted magnetic semiconductors (DMSs) have attracted much attention in recent years because of their potential applications in the field of microelectronics and spintronics [1], [2]. For practical applications, an ideal DMS system must display ferromagnetism (FM) behavior at room temperature (RT) or above. Among all DMSs, ZnO based DMSs have received much attention due to their large exciton binding energy (60 meV) and possible FM at RT. Dietl et al. [3] proposed that wide band gap semiconductors, such as GaN and ZnO, can exhibit FM property above RT with the nominal hole doping, and which was also proved by first-principle calculations on ZnO based DMSs materials [4]. Following these predictions, many research outputs have been reported on transition metal (TM)-doped ZnO with various structures, optical or magnetic behaviors and drastic debates were generated, while considering the origin of RT ferromagnetism. For instance, numerous works showed that the precipitated magnetic clusters or the appearance of secondary magnetic phases were responsible for RTFM in TM-doped ZnO [5], [6]. On the contrary, others ruled out the existence of secondary phases that can act as origin of the observed RTFM, which shows its intrinsic property [7], [8], [9]. Thus, the mechanism of RTFM in ZnO based DMSs are not yet fully understood.

Recently, TM doping as well as oxygen vacancies (VOs) have been perceived to play a significant role in the FM in oxide DMSs. It has been reported that VOs can modify the band structure of the host oxides and made it FM [10], [11]. According to the bound magnetic polarons (BMPs) model, the magnetic exchange interaction between TM ions and VOs can make all spins align in the same direction around the defects sites [12]. For example, Biegger et al. [13] and Hong et al. [14] found that the FM in Co-ZnO and Cr-ZnO films were attributed to the existence of VOs. Furthermore, RTFM induced by oxygen vacancy was observed in Ni and Cu-doped ZnO [15], [16]. Among TM elements, the RTFM in Fe-doped ZnO system has been studied extensively [17], [18], [19], [20], yet the results were not consistent. For instance, Ahn et al. [17] reported the intrinsic source of magnetism found in Fe-doped ZnO was based on the carrier mediated mechanism, while Sharma et al. [18] argued that the FM was due to extrinsic sources, such as secondary phase and cluster formation. Other groups even only gained paramagnetic behavior [19], [20]. These controversies showed that the RTFM extremely depends on preparation techniques, concentration of dopants and environmental conditions. Thus, further investigation is necessary to understand the origin of the RTFM in Fe-doped ZnO.

A number of techniques have been adopted to fabricate TM-doped ZnO nanoparticles, for example, co-precipitation [21], [22], pulse-laser deposition [14], solid state reaction [20], hydrothermal process [23] and sol-gel method [24]. Among these various synthetic approaches, hydrothermal method is widely employed because of its convenience and flexibility. Moreover, during the crystal growth in the hydrothermal reaction process, the morphology, microstructure, and physical/chemical properties of the nanoparticles can be tuned by the dissolved ions, which was responded to the applied magnetic field. It has been already proved that the applied magnetic field during reaction can significantly influence the FM of TM-doped ZnO semiconductors [25], [26], [27]. Therefore, in this work, we prepared Fe-doped ZnO plate liked nanoparticles with RTFM via hydrothermal method under high magnetic (4 T) field environment. Various characterization techniques were employed to study the microstructure, morphology, electronic state and the origin of the observed RTFM properties.

Section snippets

Specimen preparation

Fe-doped (2 at%) ZnO was prepared through hydrothermal method with high magnetic field. 0.5 mol/L of zinc acetate [Zn(CH3COO)2H2O] and the desired amount of ferric nitrate [Fe(NO3)9H2O] were dissolved in deionized (DI) water with 5 min stirring at room temperature. Then, the sodium hydroxide solution (1 mol/L) was gradually introduced into the former solution at room temperature and followed by stirring for 30 min. The entire prepared solution was transferred into a Teflon-lined autoclave and

XRD results

Fig. 1 shows the XRD patterns of pure ZnO, Fe-doped ZnO with (denoted as F/4T) and without (denoted as F/0T) high magnetic field. The diffraction peaks at (100), (002) and (101) of each sample are well indexed with the ZnO wurtzite (space group P63mc) structure. Secondary phases were not detected within the sensitivity of the XRD measurements. Comparing with pure ZnO, all the diffraction peaks of Fe-doped ZnO shifted to high angle (inset of Fig. 1). As proposed by Xia et al. [28], the peak

Conclusion

In summary, Fe-doped ZnO plate-shaped nanoparticles were successfully fabricated through hydrothermal process with (4 T) high magnetic field. The samples exhibited pure wurtzite structure and no secondary phases were detected. The applied magnetic field process can effectively enhance the concentration of Fe3+ and oxygen vacancies in ZnO matrix. Thus, the overlapping of the Fe3+-VO-Fe3+ magnetic polarons coupling is increased due to effect of oxygen vacancies, which is responsible for the

Acknowledgements

The work is financially supported by National Natural Science Foundation of China under Grant no. 51572166. The research published in the journal is the outcome of the collaboration with the project Support of R&D and International Relations in the Field of Education with the financial support from the Moravian-Silesian region. The authors also express gratitude to the Analysis and Research Center of Shanghai University for their valuable Technical Support. W. X. Li also acknowledges research

References (41)

Cited by (14)

  • Enhancement of superoxide evolution by nickel-doped for the removal of organic pollutants and cyanobacteria

    2020, Journal of the Taiwan Institute of Chemical Engineers
    Citation Excerpt :

    Therefore, BiOCl is adopted as a promising bismuth-based catalyst. And lots of subsequent attempts have been made to enhance the activity of BiOCl, such as elemental doping, creation of vacancies, and construction of heterojunctions [17–19]. Among them, doping can enhance the photocatalytic performance of the catalyst through reducing the band gap energy of the catalytic material, expanding the light absorption range, and increasing oxygen vacancies [20–22].

  • Zinc interstitial and oxygen vacancy mediated high Curie-temperature ferromagnetism in Ag-doped ZnO

    2020, Ceramics International
    Citation Excerpt :

    Among reported intrinsic ferromagnetism origins, the defect has been considered as an important factor inducing the ferromagnetism of DMSs [60,66]. At present, the theory of bound magnetic polarons related to oxygen vacancy (Vo) is frequently used to explain the ferromagnetism of ZnO based DMSs [13,22,67–70]. In this study, XPS analysis manifests that with the increase of the deposition current, the amount of Vo was improved, and the content of zinc interstitial (Zni) was reduced in Ag-doped ZnO.

  • Multicomponent Zn <inf>(1-x)</inf> Fe <inf>0.8x</inf> Na <inf>0.2x</inf> O semiconductors: Effect of dopant concentration and ionic radius on structural, opto-electronics, magnetic and sensing properties

    2019, Materials Science in Semiconductor Processing
    Citation Excerpt :

    Different transition metal doping are found in literature [15–27] showing magnetism and sensing properties. It has been reported that in Fe-doped ZnO, a VO-mediated ferromagnetic exchange interaction may generate magnetism with increasing Fe-content [28,29]. However, higher charge and lesser ri of Fe3+ compared to Zn2+ allows the lattice to hold more oxygen [10], reducing oxygen vacancy (VO).

View all citing articles on Scopus
View full text