Enhancement of zinc vacancies in room-temperature ferromagnetic Cr–Mn codoped ZnO nanorods synthesized by hydrothermal method under high pulsed magnetic field
Graphical abstract
This figure shows the magnetization versus magnetic field curves for ZnO–Cr–Mn-0T and ZnO–Cr–Mn-4T at 290 K. The 4 T sample was well-defined hysteresis loops, which is indicative of room-temperature ferromagnetic behavior. But for 0 T sample, no ferromagnetic response at 290 K is observed. The hole doping enhanced by high pulsed magnetic field is crucial to stabilize ferromagnetism in Mn-doped ZnO diluted magnetic semiconductor. And the presence of Cr3+ in 4 T sample is a possible signature of hole doping induced by zinc vacancies.
Introduction
Diluted magnetic semiconductors (DMSs), which refer to transition-metal (TM) ions partially substitute cations of the host semiconductor materials, have attracted considerable attention for potential applications in spin electronics and magnetic devices that allow the manipulation of both the spin and charge degrees of freedom [1], [2], [3], [4], [5]. The practical spintronic devices depend on the high Curie temperature (TC) exceeding room temperature. The ferromagnetic properties originate as an intrinsic feature but not the second magnetic phase. ZnO is a wide band gap (Eg∼3.3 eV at 300 K) semiconductor with a large exciton binding energy (∼60 meV) [6], [7]. Moreover, well-defined doping and defect chemistries, suitability for transparent high-power high-temperature application and the ability to lase or emit spontaneously at ultraviolet wavelengths combine to make ZnO attractive in many potential device applications [8]. In the quest for materials with high TC, TM-doped ZnO has emerged as an attractive candidate according to the theoretical studies [9], [10], [11]. In the foundations of the p-d Zener model, Dietl et al. [9] predicted that the TC of p-type ZnO (p ≥ 3.5 × 1020 cm−3) semiconductor doped with 5% Mn might be higher than room temperature. While p-type ZnO is difficult to attain because of the abundant native defects such as oxygen vacancies (VO) and Zinc interstitials (Zni). However, Sato and Katayama–Yoshida [10] theoretically demonstrated that ZnO doped with TM atoms such as V, Cr, Fe, Co, and Ni exhibit ferromagnetic stability using first-principle calculations.
Since the first claim of room-temperature ferromagnetism in Mn2+: ZnO [12], high-TC ferromagnetism has been observed in Mn2+: ZnO with p-type and n-type conductivity [13], [14]. Meanwhile, other controversial results have been claimed, including a low Curie temperature [15], spin-glass behavior [16], and presence of antiferromagnetism [17]. Thus, the origin of FM in DMSs is still ambiguous. Up to now, some interesting codoping experimental results were reported. Singhal et al. [18] reported that the codoping of Mn into Co doped ZnO further enhances the ferromagnetic ordering. Also, Aljawfi et al. [19] suggested that the ferromagnetism of Cr/Co codoped ZnO nanoparticles improve with increasing Cr doping. The codoping approach has drawn intensive attention due to the possibility to tailor the position and occupancy of the Fermi energy (Ef) of doped DMS. A key property common to all of the models describing ZnO DMS ferromagnetism is strong electronic coupling between the magnetic ions and charge carriers at the Fermi level [20]. Thus, codoping seems to be a potential approach to enhance the ferromagnetism in TM-doped ZnO DMSs.
Recently experimental studies have revealed that the magnetic properties depend strongly on fabrication conditions, concentration of dopants and the structure of materials. As to the fabrication condition, the TM-doped ZnO can be synthesized by chemical vapor deposition, physical vapor deposition, solid state reaction, hydrothermal, sol–gel etc. [21], [22], [23], [24], [25]. Among these methods, hydrothermal method becomes the most efficient choice for its advantages of easy control and uniform products [26]. So far, the magnetic field has been applied as an effective way to influence the crystal growth, morphology and the properties of nanomaterial, such as Cr-doped ZnO [27], Fe3O4 nanowires [28], Co3O4 nanocubes/nanospheres [29], and so on. It can be found that an external magnetic field influences significantly the growth behavior and the exchange interactions between the spins in the nanoparticles during the hydrothermal process. In view of this, the effect of pulsed magnetic field on the magnetic property of TM-codoped ZnO prepared by hydrothermal method is really expected. The present article accounts for the structural and magnetic properties of 1%Cr–1%Mn (at. %, nominal doping amount) codoped ZnO synthesized by hydrothermal method under high pulsed magnetic field.
Section snippets
Experimental details
Potassium hydroxide solution (1.33 M) was slowly dropped into the zinc acetate solution (1.00 M) and stirred for 0.5 h. Then, chromium chloride solution (0.01 M) and manganese acetate solution (0.01 M) were slowly dropped into the mixture followed by stirring for another 0.5 h. The mixture was transferred into Teflon-lined titanium alloy autoclave, and maintained at 200 °C for 4 h under 4 T pulsed magnetic field. Finally, the reacted products were washed with deionized water three times and
XRD analysis
Fig. 1 shows XRD patterns of the samples with and without pulsed magnetic field during the hydrothermal method and pure ZnO sample. All the diffraction peaks can be indexed to the hexagonal wurtzite structure of the ZnO (JCPDS no. 36–1451) with P63 mc space group. Within the sensitivity of XRD measurement, no distinct secondary phases related to Cr or Mn element was observed. The detail in the range of 30–40° as inserted in Fig. 1, presents that the peaks, such as (), (0002) and (),
Discussion
Over the past decade, there might be two possible theories to explain the phenomena of room-temperature ferromagnetism (RTFM) for the DMS system. Firstly, the secondary phases were regarded as a source of the spurious RTFM. In this study Cr and Mn ions were found to be successfully incorporated into the wurtzite lattice at the Zn2+ sites without any secondary phases formed according to XRD, HRTEM, XPS and Raman results. That is, the ZnO–Cr–Mn-4T sample has intrinsic ferromagnetism. Secondly,
Conclusions
In summary, room-temperature ferromagnetic Cr–Mn codoped ZnO nanoparticles were synthesized by hydrothermal method with pulsed magnetic field. The sample is hexagonal wurtzite structure without any secondary phases. Mn ions were incorporated into the ZnO wurtzite host matrix with divalent state, but the valence state of Cr ions became trivalent states in the 4 T sample. The room temperature ferromagnetism was observed in the ZnO–Cr–Mn-4T sample by M−H and ZFC/FC curves. The hole doping enhanced
Acknowledgments
This work was financially supported by Shanghai Science and Technology Commission (11nm0501600). The authors thank the Analysis and Research Center of Shanghai University for their technical support.
References (52)
Study of electronic and magnetic properties of vacuum annealed Cr doped ZnO
J. Alloys Compd.
(2012)- et al.
Effects of Ni concentration on structural, magnetic and optical properties of Ni-doped ZnO nanoparticles
J. Alloys Compd.
(2014) - et al.
A comparative study on the ferromagnetic properties of undoped and Mn-doped ZnO
J. Alloys Compd.
(2012) - et al.
Effect of Co substitution on the structural and optical properties of ZnO nanoparticles synthesized by sol-gel route
J. Alloys Compd.
(2011) - et al.
Ab initio study of ZnCoO diluted magnetic semiconductor and its magnetic properties
J. Alloys Compd.
(2013) - et al.
Surface defect mediated magnetic interactions and ferromagnetism in Cr/Co Co-doped ZnO nanoparticles
J. Magn. Magn. Mater.
(2013) - et al.
Multi-roles of Cu ions in the ferromagnetic properties of (Cu, Al)-codoped ZnO thin films
J. Cryst. Growth
(2011) - et al.
Different magnetic origins of (Mn, Fe)-codoped ZnO powders and thin films
Mater. Res. Bull.
(2012) - et al.
Room temperature ferromagnetism in hydrothermally grown Ni and Cu co-doped ZnO nanorods
Ceram. Int.
(2013) - et al.
Enhancement of ferromagnetic properties in Zn0.98Cu0.02O by additional Co doping
J. Alloys Compd.
(2013)
Effects of temperature on the microstructure and magnetic property of Cr-Doped ZnO DMS prepared by hydrothermal route assisted by pulsed magnetic fields
J. Chem.
Nanostructure and optical properties of M doped ZnO (M = Ni, Mn) thin films prepared by sol–gel process
Phys. B
X-ray photoelectron spectroscopy and auger electron spectroscopy studies of Al-doped ZnO films
Appl. Surf. Sci.
Intrinsic ferromagnetic properties in Cr-doped ZnO diluted magnetic semiconductors
J. Solid State Chem.
Effects of hydrogen annealing on the room temperature ferromagnetism and optical properties of Cr-doped ZnO nanoparticles
J. Magn. Magn. Mater.
A study of structural, optical and magnetic properties of Zn0.97−xCuxCr0.03O diluted magnetic semiconductors
J. Alloys Compd.
Structure and magnetic properties of Cr-doped ZnO nanoparticles prepared under high magnetic field
Solid State Commun.
Effect of defects on room-temperature ferromagnetism of Cr-doped ZnO films
Scr. Mater.
Room-temperature ferromagnetic properties of Ni-doped ZnO rod arrays
Phys. E
Characteristics of nickel-doped zinc oxide thin films prepared by sol–gel method
Surf. Coat. Technol.
Raman spectroscopy study of ZnO-based ceramic films fabricated by novel sol–gel process
Mater. Sci. Eng. B
Room temperature ferromagnetism in Mn-doped dilute ZnO semiconductor: an electronic structure study using X-ray photoemission
J. Alloys Compd.
Properties of Co/Ni codoped ZnO based nanocrystalline DMS
J. Magn. Magn. Mater.
Enhanced ferromagnetism in single crystalline Co-doped ZnO thin films by Al codoping
J. Alloys Compd.
Structural and magnetic studies on transition metal (Mn, Co) doped ZnO nanoparticles
J. Magn. Magn. Mater.
Making nonmagnetic semiconductors ferromagnetic
Science
Cited by (22)
Chemical methods for the growth of oxides
2023, Defect-Induced Magnetism in Oxide SemiconductorsZinc interstitial and oxygen vacancy mediated high Curie-temperature ferromagnetism in Ag-doped ZnO
2020, Ceramics InternationalCitation Excerpt :Since Ag and its oxides are nonmagnetic, it can be deduced that the ferromagnetism in Ag-doped ZnO DMSs belongs to intrinsic ferromagnetism. 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].
Study on the high magnetic field processed ZnO based diluted magnetic semiconductors
2019, Ceramics InternationalCitation Excerpt :In addition, in Cr–Ni codoped ZnO synthesized under 0 T or 4T magnetic field, both Cr and Ni ions remained divalent. Differently, for Cr–Mn codoped ZnO prepared by Zhong M et al. [81], Mn ions kept divalent, while Cr ions changed from divalent to trivalent by employing 4T HMF in hydrothermal synthesis, which was attributed to the emergence of VZn induced by HMF. Thus, as shown in Fig. 26, it was inferred that the appearance of RTFM caused by HMF in Cr–Mn codoped ZnO was due to the presence of VZn.
Extraordinary visible photocatalytic activity of a Co<inf>0.2</inf>Zn<inf>0.8</inf>O system studied in the Remazol BB oxidation
2019, Journal of Photochemistry and Photobiology A: ChemistryCitation Excerpt :However, a slight offset between the peaks of CoxZn1-xO phase and ZnO phase suggests that Co doping is occurring [14,15]. The radius of Co2+ (0.65 Å) is smaller than that of Zn2+ (0.74 Å) [16], thus it is expected that cobalt ions may be introduced into the ZnO lattice. No other XRD peaks related to cobalt oxides are detected; suggesting that cobalt ions may have been successfully incorporated into the lattice ZnO as dopants [17].