Absence of room temperature ferromagnetism in Mn-doped ZnS nanocrystalline thin film
Highlights
► The Mn-doped ZnS nanocrystalline films were synthesized. ► The crystal structure of the films has been determined. ► Surface morphology using atomic force microscopy has been investigated. ► The magnetic properties of the films were studied.
Introduction
It is known that replacement of magnetic ions like Mn, Cr, Fe, Co, and Ni into non-magnetic II–VI host semiconducting matrix leads to a new class of materials with their potential spintronics applications, known as diluted magnetic semiconductors (DMS) [1], [2]. The theoretical approach predicated by Dietl et al. [3], the existence of ferromagnetic semiconductors at room temperature, motivated many researchers for reporting experimental works about the appearance of room temperature ferromagnetism in transition metal (TM) doped semiconductors.
Furthermore, a lot of work has been done for the synthesis of novel DMS films with room temperature ferromagnetism based on III–V and II–VI compound semiconductors. However, transition metal doped II–VI semiconductor compounds are getting attention as transition metal semiconductors based on III–V have lack of solubility [3], [4]. II–VI compound semiconductors doped with magnetic ions have been obtained with various properties such as ferromagnetism [5], spin glass behavior [6] and paramagnetism [7]. Among these materials synthesis of non-magnetic semiconductor ZnS doped with Mn2+ ions in the form of thin film and the study of their magnetic properties is much more important for their potential application in spintronic device [8], such as magnetic sensors, electro-optic modulators, photoconductors, light emitting materials, filed effect transistors and magneto-optical devices [9], [10]. During the last few years the DMS doped with Mn2+ ions have extensively studied, specially their magnetic and semiconducting properties [8]. Low temperature (TC) around 30 K had been reported in Mn-doped ZnS nanoparticles for doping above 1.5% by Sarkar et al. [11]. On the other hand, magnetic measurements performed by Tsujii et al. [12] and Zuo et al. [13] report antiferromagnetic and paramagnetic orderings at low temperature even down to 4 K, respectively. However, EPR studies by Lakshmi et al. [14] for nanocrystalline samples of Zn1−xMnxS (x=0.0, 0.02, 0.04) synthesized by the chemical precipitation method showed an evidence of ferromagnetism around room temperature. These magnetic properties were found to be strongly dependent on the synthesis method, the concentration of TM atoms and the sample preparation conditions. However, such discrepancy in the magnetic properties reveals that some controversy still exists concerning the appearance of ferromagnetism in Mn-doped DMS [2], [15].
In this paper, we reported the magnetic properties of the electron beam evaporated Mn-doped ZnS nanocrystalline thin films with different Mn concentration deposited on glass substrate.
Section snippets
Experimental details
The Mn-doped ZnS thin films with different Mn content (Zn1−xMnxS) x=0.02, 0.05, 0.1, and 0.15 were deposited on amorphous glass substrates maintained at room temperature prepared by electron beam evaporation using high vacuum coating unit type Edward Auto 306. The ceramic samples of Zn1−xMnxS were synthesized by the solid state reaction method from stoichiometric amounts of high-purity ZnS (99.999%) and MnS (99.999%) powders (MV Lab. INC., USA). The thickness of the films was kept to be
Results and discussion
The X-ray diffraction patterns (XRD) of the as deposited Zn1−xMnxS thin films for different Mn doping concentration (x=0.02, 0.05, 0.1, and 0.15) are presented in Fig. 1. The diffraction peaks of all the films which correspond to the planes (100), (002), (110) and (112) can be well indexed on the basis of hexagonal wurtzite ZnS type structure (JCPDS no. 36-1450) without additional diffraction peaks for Mn metal clusters and Mn compounds (sulfides, oxides, etc.) or other detectable secondary
Conclusions
We have successfully synthesized single phase Zn1−xMnxS (x=0.02, 0.05, 0.1 and 0.15) diluted magnetic semiconductors nanocrystalline thin films by the electron beam evaporation technique. XRD showed a single phase with hexagonal structure and the lattice parameters varied linearly with Mn content. Grain size was found to vary from 12 to 19 nm with the increase of Mn content which is comparable to those values estimated from AFM investigations. Superparamagnetic behavior is observed at lower
Acknowledgments
This work was supported by the Deanship of the Scientific Research at Qassim University, Kingdom of Saudi Arabia in the framework of the Long-Term comprehensive National Plan for science, technology and innovation, under Grant no. 09-ENV792-09.
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