| Description |
SnO2 is one of the well known wide band gap semiconductors and doping trace amount of transition element can give rise to robust ferromagnetic semiconductor for potential applications in optoelectronic and spintronic devices. Co and Ni doped SnO2 up to a doping level of 10 at % were prepared by using solid state route and mechanical synthesis and were sintered at 900oC. The XRD patterns recorded for Co-doped and Ni-doped SnO2 samples were refined by using P42/mnm space group. The typical lattice parameters for 2 at % Co doped SnO2 were found a = b = 4.733 Å, c = 3.184Å and a = b = 4.739 Å, c =3.188 Å for 2 at % Ni doped SnO2. The average crystallite size was estimated to be around 40nm. The phase purity and composition of the doped samples were also studied from EDX, TEM and Raman analysis. The oxide diluted magnetic semiconductors obtained by doping Co and Ni in SnO2 are found to exhibit room temperature ferromagnetism with high Tc beyond room temperature. The typical saturation magnetization for 2 at % Co doped sample was found to be 2.9 emu/g at room temperature and it enhances to 5.9 emu/g (7.9 µB/Co-ion) at 20K. Such a high Msi value can be explained in terms of unquenched d-orbital of the doped Co-ion. The typical Curie temperature for 2 at % Co and Ni doped SnO2 are found to be 692 K and 803 K respectively. The observed ferromagnetism in these samples could be mostly explained on the basis of the formation of bound magnetic polarons. The value of spontaneous moment per BMP, meff is found to be in the order of 10-17 emu and increases marginally with increase in Co concentrations. The radius of BMP was found to be in the range of 60 Å to 40 Å. Also, we have studied the critical behavior of 2 at % Co SnO2 sample by analyzing the magnetization data in terms of modified Arrott plot method and, independently by Kouvel-Fisher method. The sample is found to exhibit a second order phase transition. The critical exponents β, γ and δ corresponding to spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively, were determined and the values are found to be comparable to the predicted values by the Mean field model. The temperature variation of effective critical exponent was determined and was found to show the characteristic behavior of disordered system.
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