Introduction of Mn2+ions into ZnO in the form of Zn(1-x)MnxO (0.00≤x≤0.25) has been done by means of coprecipitation method at low temperature using Zn(CH3COO)2·2H2O, Mn(CH3COO)2·4H2O, HCl, and NH4OH as starting materials. The XRD analysis showed that the produced Zn(1-x)MnxO (0.00≤x≤0.09) samples were crystallized in single phase of wurtzite with hexagonal structures. Besides the wurtzite, the presence of the secondary phase of hetaerolite ZnMn2O4with tetragonal structures was detected in the samples having 0.10≤x≤0.25. The nanometer-sized Zn(1-x)MnxO crystals obtained from XRD analysis were well confirmed by SEM and TEM images. The electron diffraction data showed that the secondary phase formed even for 0.01 and 0.10 Mn-doping samples were ZnMn2O4and MnO2. The VSM data indicate that the paramagnetic properties of Mn doping occurred at 0.00≤x≤0.06 and 0.10≤x≤0.25 as well as superparamagnetic properties occur in Mn doping 0.07≤x≤0.09. The most interesting fact in this study was the formation of secondary phases in all Mn-doped ZnO samples, even for the smallest x of 0.01.
Decomposition of composite multi-path signals is a complex problem. The windowing approach in the time domain cannot be used for overlapping signals. While the filtering approach in the frequency domain cannot separate the overlapping signal spectrum. One of the key solutions to this problem is to estimate the time-delay for each signal component. This study discusses techniques for separating multi-path signal components through time-delay estimation by analysing residual signal and its correlation with original signal. The residual signal is the error between the reference and the received signal. Overlapping multi-path signal components are detected in two different approaches. First, when the residual signal is random, the whiteness analysis is applied to detect the signal component. Second, when the whiteness test failed, which means the residual signal has a correlation with the reference signal, the correlation test can then be applied. The simulation results show that this proposed method successfully detected the signal components.
Effects of Mn-substitution on magnetic properties of Zn1-xMnxO (MZO) nanoparticles with x= 0.00, 0.03, 0.05 and 0.07 have been investigated along with their local structure. Study on Mn K-edge XANES spectra of MZO reveals that the oxidation state increases by Mn-substitution, which further implies that MZO exhibits a mixed valence state of Mn3+/Mn4+. The local structure analysis on Mn K-edge EXAFS spectra shows that the coordination number (CN) of Mn reduces by increasing Mn concentration, thus the amount of oxygen vacancy (VO) increases by Mn-substitution. Interestingly, the magnetization of MZO also tend to increase as the Mn concentration increases. The M(H) curves exhibit a linear (paramagnetic) behavior, showing no evidence of room-temperature ferromagnetism. Our results show that magnetism of MZO is related to the correlation between Mn magnetic moment and VO.
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