Ferromagnetism in sphalerite and wurtzite CdS nanostructures

Zhaolong Yang,Zhenhua Shi,Desheng Xue,Daqiang Gao,Zhonghua Zhu,Jing Zhang,Zhipeng Zhang

doi:10.1186/1556-276x-8-17

Abstract

Room-temperature ferromagnetism is observed in undoped sphalerite and wurtzite CdS nanostructures which are synthesized by hydrothermal methods. Scanning electron microscopy and transmission electron microscopy results indicate that the sphalerite CdS samples show a spherical-like shape and the wurtzite CdS ones show a flower-like shape, both of which are aggregated by lots of smaller particles. The impurity of the samples has been ruled out by the results of X-ray diffraction, selected-area electron diffraction, and X-ray photoelectron spectroscopy. Magnetization measurements indicate that all the samples exhibit room-temperature ferromagnetism and the saturation magnetization decreases with the increased crystal sizes, revealing that the observed ferromagnetism is defect-related, which is also confirmed by the post-annealing processes. This finding in CdS should be the focus of future electronic and spintronic devices.

Highlights

Since the first discovery of ferromagnetism (FM) in Mndoped GaAs [1], great effort has been paid to search for intrinsic dilute magnetic semiconductors (DMSs) with Curie temperatures (Tc) at or above room temperature (RT) by doping semiconductors with transition metals (TMs) [2,3]
The mechanism of the observed FM remains controversial theoretically, which mainly includes experimental artifacts, segregation of secondary ferromagnetic phases, magnetic clusters, and indirect exchange mediated by carriers, electrons, and holes associated with impurities that are related to the observed room-temperature ferromagnetism (RTFM) [4,5,6,7]
It can be clearly seen from the high-resolution TEM (HRTEM) of sample S1 in Figure 2d that a singlecrystalline grain is about 4 nm in diameter, which is consistent with the X-ray diffraction (XRD) result, and it has a lattice spacing of 0.21 nm equaling to the interplanar spacing of the sphalerite CdS in (220) plane

Summary

Introduction

Since the first discovery of ferromagnetism (FM) in Mndoped GaAs [1], great effort has been paid to search for intrinsic dilute magnetic semiconductors (DMSs) with Curie temperatures (Tc) at or above room temperature (RT) by doping semiconductors with transition metals (TMs) [2,3]. During the past few years, room-temperature ferromagnetism (RTFM) has been reported in TM-doped DMSs experimentally. The mechanism of the observed FM remains controversial theoretically, which mainly includes experimental artifacts, segregation of secondary ferromagnetic phases, magnetic clusters, and indirect exchange mediated by carriers, electrons, and holes associated with impurities that are related to the observed RTFM [4,5,6,7]. Lots of investigations have demonstrated FM with Tc above room temperature observed in transition metal ion (such as Fe, Co, Cr, Mn, and V)-doped CdSbased low-dimensional materials [26,27,28,29,30]. Pan et al demonstrated that FM can be realized in CdS with C doping via substitution of S which can be attributed to the hole-mediated double-exchange interaction [18].

Methods

Results

Conclusion