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Structural, Optical and Magnetic Properties of Co
doped ZnSe Powders
P Mallikarjuna, J Sivasankar, M Rigana Begam, N Madhusudhana Rao, S
Kaleemulla, J Subrahmanyam
To cite this version:
Structural, Optical and Magnetic Properties of Co doped ZnSe Powders
45P. Mallikarjuna1, J. Sivasankar1, M. Rigana Begam2, N. Madhusudhana Rao2,a, S. Kaleemulla2, J. Subrahmanyam3
1 – Department of Physics, Rayalaseema University, Kurnool, AP, India
2 – Thin Films Laboratory, Center for Crystal Growth, School of Advanced Sciences, VIT University, Vellore, TN, India 3 – Department of Physics, N.B.K.R. S&A College, Vidyanagar, India
a – drnmrao@gmail.com
DOI 10.2412/mmse.90.5.465 provided by Seo4U.link
Keywords: solid-state reaction, X-ray diffraction, optical studies, Co doped ZnSe.
ABSTRACT. Co doped ZnSe nano crystalline powder samples were prepared by solid-state reaction method.Structural,
optical and magnetic properties of pure and Co doped ZnSe powders were studied. Both Pure and doped ZnSe samples were in cubic structure. Lattice parameter and band gap of pure and doped ZnSe powders decreased with increase of Co concentration. The Raman shift in the Raman spectra of the samples confirms the Co doping in to the ZnSe lattice.Band gap of the samples decreased with increase of Co concentration. Codoped ZnSe powders exhibited half-metallic ferromagnetism at room temperature with low Co concentration and paramagnetism with high Co concentration.
Introduction.Dilute magnetic semiconductors (DMS) have earned good interest in recent years
because of its feasibility to have magnetic and semiconducting properties in the same materials.DMS materials are the traditional non-magnetic semiconductors doped with transition metal or rare earth metal ions at very low concentration. The host material is exhibiting some peculiar properties after doping with suitable transition metal ions[1]. DMS materials find more attention because of their applications inopto-electronics and spintronics devices, which utilizesboth the spin and charge of the electrons[2, 3]. Further these find significant role in designing of spin valves, spin light emitting diodes and ultra-fast optical switches[4]. Extensive studies had been carriedout on several II-VI DMS compounds.Among all II-VI semiconductors, ZnSe is a potential candidate to fit in various applications as solar cells [5], bio-medical tags [6]and light emitting diodes [7].ZnSe is a blue-lasing material and can be employed in designing modulated hetero structures and optical wave guides[8]. Doping magnetic ions of +2 oxidation state into II-VI DMS such as CdSe, CdTe and ZnSe is easy.Co is one of the suitable ferromagnetic transition metal to dope in to II-VI semiconductors. Different model or mechanisms such as double exchange, RKKY carrier induced intractions, super- exchange were applied to explain the origin of ferromagnetism in these II-VI DMS compounds [9, 10]. The present work focus on the effect of Co doping concentration on structural, optical and magnetic properties of Co doped ZnSe powders.
Experimental details.Pure and Co doped ZnSe powder samples were prepared with different
concentrations of Cobalt by solid state reaction. There sets of powders 1: pure ZnSe, sample-2: 5at. % Co doped ZnSe and Sample-3:10 at.% Co doped ZnSe were prepared. Stoichiometric quantities of ZnSe and freshly prepared Co doped ZnSe were weighed and subjected to continuous mechanical grinding for about14-16 hours.Thepowders were sintered at 800oC for 10 hours under a
45
pressure of 10-3mbar.The pure ZnSe and Co doped ZnSe powders were characterized to study their structural, raman, optical and magnetic properties.
Results and Discussion.
Structural analysis.Fig.1 shows the X-ray diffraction patterns of the pureZnSe and Co doped ZnSe
powder samples at different Co doping concentrations. The diffraction peaks of all the samples are found to be matched with ZnSe cubic structure pattern having JCPDS data [card no 88-2345].The crystal structure of the host material has not been altered on increasing dopant concentration. These observations indicate that Co ions were doped in the corresponding metal sites of Zn ions.It is also observed from the XRD studies that the intensity of the peaks increased as the concentration of the dopant ions of cobalt increased from 5% to 10%.
0 5 000 10 000 15 000 20 000 25 000 2 0 3 0 40 50 6 0 70 0 5 000 10 000 15 000 0 5 000 10 000 15 000 20 000 25 000 Zn S e:Co (10% ) (1 1 1 ) ( 2 0 0 ) (2 2 0 ) (3 1 1 ) (2 2 2 ) (4 0 0 ) In te n s it y a .u 2 th eta (d eg ree) Pu re Zn S e Z nS e:Co (5%)
Fig. 1. XRD patterns of pure ZnSe and Co doped ZnSe powders.
0.00 0.02 0.04 0.06 0.08 0.10 5.59 5.60 5.61 5.62 5.63 5.64 5.65 5.66 L a tt ice p a ra m e te r (a )(A )
Cobalt com position(X)
Fig. 2. Variation of lattice parameter of Co doped ZnSe with Co concentration.
287 cm-1 are attributed to the second transverse acoustic (2TA), transverse optical (TO) and longitudinal optical (LO) phonon modes of ZnSe, respectively. The observations agree well with the reported results for ZnSenanobelts and nanowires [13].All the aboveresults further confirm that the as-prepared products present a cubic structure of ZnSe phase. Fig. 4 shows the EDAX spectra and SEM images of Cr doped CdSe powders. EDAX spectra confirm the existence of Cr in the powder samples and SEM images illustrate that the Cr doped CdSe powder are in submicron size.
Fig. 3. Raman spectra of pure ZnSe and Co doped ZnSe powders.
a) b)
c) d)
Optical properties. Fig. 5 shows the diffused reflectance spectra of pure and Co doped ZnSe
powders. The bandgaps for different substitutions of Co ions (x=0.05, 0.10) are calculated using Tauc’s relation as shown in the Fig.6.It can be found that the band gaps of Co doped ZnSetend to decrease from 2.378 eV (pure ZnSe) to 2.199eV and 1.835eV.The red shift in the band gap with increase in Co doping can be explained on account of the sp-d exchange interaction taking place between the conduction band electrons and the localized ‘d’ electrons of Co ions that replace the host Zn ions. Babuet. al. also observed same trend of decrease in band gap with increase of dopant concentration in Mn doped ZnSe thin films up 15 at. wt. % of Mn concentration [14].
Magnetic properties. The M-H curves for Co doped ZnSe powders at room temperature are showed
in the Fig.7. Inset of the Fig. 7 shows the M-H curve of pure ZnSe at room temperature. It confirms that ZnSe is diamagnetic in nature. Themagnetization values (Ms) observed in the present samples
for5at% and 10at% Co concentrations are 0.024088 emu/g and 0.05728 emu/g.
In general the manifestation of ferromagnetic behavior in DMS compounds may be understood from the mutual exchange interaction present between free delocalized charge carriers and d spins of Co ions. But these Co doped ZnSe samples exhibit half metallic ferromagnetism. This type of magnetism is attributed due to polarization of electronic spins.
Benstaali et.al.[15] in Co doped ZnSe, Mohamood et. al.[16] in Ti doped ZnSe and Arifet. al. [17] in Co doped CdSe were reported half metallic ferromagnetism due to polarization of the spin in their theoretical investigation and further suggested these materials are suitable for spintronic materials.
500 1000 1500 2000 2500 20 40 60 80 100 R e fl e c ta n c e ( % ) Wavelength (nm) Pure x = 0.05 x = 0.10
Fig. 5. Diffused reflectance spectra of undoped and Co doped ZnSe powders
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 [ h ] h (eV ) Pure ZnSe ZnSe:Co(5%) ZnSe:Co(10%)
MMSE Journal. Open Access www.mmse.xyz - 1 0 0 0 0 - 5 0 0 0 0 5 0 0 0 1 0 0 0 0 - 0 . 0 6 - 0 . 0 5 - 0 . 0 4 - 0 . 0 3 - 0 . 0 2 - 0 . 0 1 0 . 0 0 0 . 0 1 0 . 0 2 0 . 0 3 0 . 0 4 0 . 0 5 0 . 0 6 - 1 0 0 0 0 - 5 0 0 0 0 5 0 0 0 1 0 0 0 0 -0 .0 1 5 -0 .0 1 0 -0 .0 0 5 0 .0 0 0 0 .0 0 5 0 .0 1 0 0 .0 1 5 M ag n eti s ati o n (e m u /g ) M a g n e ti c f i e ld ( g a u s s ) P u r e Z n S e Z n0 .9 5 C o0 . 0 5S e Z n0 .9 0C o0 .1 0 S e A t 3 0 0 K M o m e n t/ m a s s (e m u /g ) F i e l d ( G )
Fig.7. M-H plots of pure ZnSe and Co doped ZnSe powders.
Summary. ZnSe powders doped with Co were synthesized by solid state reactions andinvestigations
were carried at different concentrations of Zn1-xCoxSe (x=0.05 and x=0.10) and studied the effect of
Co concentration on structural, optical and magnetic properties of the prepared samples. The X-ray diffraction studies and Raman analysis confirmed that all the samples are in cubic structure. Optical studies denote a decrease in band gap with increase in Co compositions. Half metallic ferromagnetism is observed in the present Co doped ZnSe powder samples at room temperature.
Acknowledgement. Authors are very much thankful to VIT-SIF for providing XRD and DRS
facilities to carry out the present work. Authors also render their sincere thanks to SAIF-IIT Madras, Tamilnadu, India, for providing vibrating sample magnetometer facilities.
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Cite the paper P. Mallikarjuna, J. Sivasankar, M. Rigana Begam, N. Madhusudhana Rao, S. Kaleemulla, J. Subrahmanyam
(2017). Structural, Optical and Magnetic Properties of Co doped ZnSe Powders. Mechanics, Materials
