Experimental and discussion
Figure 1 presents the XRD patterns of ZnO doped with MnO where the phases of spinel, manganese oxide and zinc oxide are present in the system. In samples n(MnO)/(1-n)ZnO (n=0.05 to 0.50) (Fig. 1A) two phases: ZnO and ZnMnO are observed. With increasing MnO concentration the content of ZnO phase decreases and the peak attributed to this phase disappears in 3 sample containing 60 wt. % of MnO (40 wt.% of ZnO) (Fig. 1B). The peak of ZnO disappears, because all zinc is now bonded in the spinel phase (Fig. 2). In samples containing 60 wt.% MnO and more, the phases of ZnMn O and Mn O are determined. XRD method was applied as well to determine a mean crystallite size in prepared samples, using the Scherrer's formula. 2 4 3 4 It was found that the mean crystallite size of ZnMnO varied from 8 to 13 nm, depending on the content of MnO (Fig. 3). 3
Figure 4 presents the results of specific surface area and density measurements. The increase of ZnO concentration in sample causes a drop of specific surface area and an increase of density. It is also illustrated by SEM images showing the morphology of samples (Fig. 5). The powders containing more manganese oxide are less agglomerated than the samples with a
2
lower content of MnO. Additionally, the agglomerates should be more stable, because the specific surface area drops from 14 to 4 m /g.
Figure 6 presents the magnetic resonance spectra of a series of ZnO-Mn O -ZnMnO -ZnMn O samples containing from 5 to 95 wt.% of MnO. The magnetic resonance spectra are 3 4 3 2 4 dominated by a slightly asymmetric and very intense, broad line. The resonance lines are centered at g ~1.889-2.011 with linewidths in the range of 741-2700 Gs (Table 1). The intensity of eff the line strongly depends on concentration of magnetic ions. The linewiths are broadened and intensities change stronger than for system FeO-Fe O -ZnFe O [13,14]. The EPR spectra 2 3 2 4
6
from very small concentration of isolated manganese(II) ions ( S ground state) is recorded for samples containing low concentration of the manganese oxides. More intense broad line is 5/2 overlapping this signal and the intensity of this spurious phase is not increasing with increasing concentration of manganese oxide.
The magnetic resonance study of
ZnO-MnO nanoparticles system
1,2
2
2
3
3
N. Guskos , G. Zolnierkiewicz , J. Typek , D. Sibera , U. Narkiewicz ,
4
and W. £ojkowski
1
Solid State Section, Department of Physics, University of Athens, Panepistimiopolis, 15 784, Greece
2
Institute of Physics, West Pomeranian University of Technology, Al. Piastow 48, 70-311 Szczecin, Poland
3
Institute of Chemical and Environmental Engineering, West Pomeranian University of Technology, Al. Piastow 17, 70-310 Szczecin, Poland
4
Institute of High Pressure Physics, Polish Academy of Science, Soko³owska 29/37, 01-142 Warsaw, Poland
30 35 -ZnMnO3 -ZnO in te n s it y 2q [deg] 5% MnO 10% MnO 20% MnO 30% MnO 40% MnO 50% MnO 30 35 40 in te n si ty ZnMn 2O4 ZnMn 2O4 ZnMn 2O4 2q[deg] 60% MnO 70% MnO 80% MnO 90% MnO 95% MnO -Mn 3O4 1000 2000 3000 4000 5000 6000 7000 -4000 -3000 -2000 -1000 0 1000 2000 3000 3000 3500 4000 -2000 -1000 0 1000 2000 3000 d /d H [A rb . u n it s ] Magnetic field H [Gs] d c ¨/ d H [A rb . u n it s ] Magnetic field H [Gs] 5% 20% 30% 40% 50% 1000 2000 3000 4000 5000 6000 7000 -5000 0 5000 d /d H [A rb . u n it s ] Magnetic field H [Gs] 60% 95% 80% 90% 70% 1000 2000 3000 4000 5000 -40000 -30000 -20000 -10000 0 10000 20000 30000 40000 d c /d H [A rb . u n it s ] Magnetic field H [Gs] 10 %
Abstract
Fine particles composed of n(MnO)/(1-n)ZnO (n=0.05 to 0.95) were prepared by wet chemistry method. According to XRD analysis samples with n=0.95, 0.90, 0.80, 0.70, 0.60 contained Mn O and ZnMn O3 4 2 4 phases, other samples contained ZnMnO and ZnO phases. The mean 3 crystalline size of ZnMnO varied from 8 to 13 nm. The magnetic 3 resonance investigations have been carried out at room temperature. An almost symmetric and very intense magnetic resonance line is recorded for all samples. The magnetic resonance spectra parameters showed marked differences with increasing n that is mainly due to the variation of the magnetic susceptibility and a much slower evolution of spin relaxation, associated with the interaction of crystal field and superexchange interactions. With increasing n the relative intensity increases while the resonance field and linewidth is reaching a maximum for n=0.5.
Experimental
The mixture of manganium and zinc hydroxides was obtained by addition of an ammonia solution to 20% solution of proper amount of Zn(NO ) ·6H O and Mn(NO ) ·4H O in water. The 3 2 2 3 2 2
0
obtained hydroxides were filtered, dried and calcined at 300 C during 1 hour. A series of samples containing n(MnO)/(1-n)ZnO (n=0.05 to 0.95) was obtained.
The phase composition of the samples was determined using XRD (Co radiation, X'Pert Ká Philips). The mean crystallite size of these phases was determined using Scherrer's formula. The morphology of samples was investigated using scanning electron microscopy (LEO 1530).
The specific surface area of the nanopowders was determined by BET method (nitrogen adsorption) using the equipment Gemini 2360 of Micromeritics. The helium pycnometer AccuPyc 1330 of Micromeritics was applied to determine the density of powders.
The measurements of magnetic resonance spectra were performed on conventional X-band (í = 9.4 GHz) Bruker E500 EPR spectrometer with 100 kHz magnetic field modulation. Samples containing around 20 mg sample powder were placed in 4 mm diameter quartz tubes. The measurements were carried out at room temperature.
Sample composition (wt% of MnO) Hr [Gs] geff Linewidth ÄHpp [Gs] Intensity ratio I%/I5% 5 3362(3) 2.000(2) 741(1) 1 20 3350(3) 2.007(2) 2480(2) 4034 30 3340(2) 2.011(2) 2600(2) 6038 40 3360(2) 2.001(2) 2700(2) 10669 50 3610(3) 1.863(2) 3500(3) 13225 60 3500(3) 1.921(2) 2200(2) 11200 70 3530(3) 1.905(2) 2350(2) 15201 80 3570(3) 1.883(2) 2350(2) 11700 90 3560(3) 1.889(2) 2330(2) 14300 95 3560(3) 1.889(2) 2410(2) 15483 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 14 Concentration of ZnO [wt.%] S p e ci fic su rf a ce a re a [m 2 /g ] 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 D e n sit y [g /c m 3 ]
Fig. 5. SEM image of ZnO-MnO powders. A- 95% MnO, B- 80% MnO, C- 50% MnO, D- 20% MnO.
Fig. 1. The XRD patterns of ZnO doped MnO. Peaks attributed to ZnO are marked as ¦ , peaks attributed to ZnMnO are marked as (3 A). Peaks attributed to Mn O are 3 4
marked as ,peaks attributed to ZnMn O are marked as vertical line.2 4
? ¡
Fig. 2. Deconvolution of a fragment of XRD signal for the sample
containing 40% ZnO/ 60% MnO.
Fig. 3. The mean crystallite size of
ZnMnO as a function of MnO 3
concentration. Table 1. The values of magnetic resonance spectra parameters.
Fig. 4. Dependence of specific surface area and density
on ZnO concentration. Fig. 6. The EPR/FMR spectra for all samples of fine particles composed of n(MnO) /(1-n)ZnO (n=0.05 to 0.95) registered at room temperature.
