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Pure 2 based wide band gap semiconductors were prepared by mechanical alloying method by using steel and tungsten carbide vials. They were further annealed at 900°C. The XRD patterns could be refined by using P42/ space group with typical lattice parameters a = b = 4.7322 Å and c = 3.1848 Å. The as milled powders obtained from both the vials exhibit room temperature ferromagnetism (FM) without any transition element doping. However upon annealing, the FM was destroyed in one of the samples. The observed FM is explained in terms of oxygen vacancy and defects induced electrons and exchange interaction between them. The ferromagnetic transition temperature obtained from the temperature variation of magnetization was found to be 915 K. The initial magnetization data could be analyzed in terms of bound magnetic polaron model. The resonance field shift in electron spin resonance spectrum is explained in terms of observed ferromagnetism. [ABSTRACT FROM AUTHOR]

Pure 2 based wide band gap semiconductors were prepared by mechanical alloying method by using steel and tungsten carbide vials. They were further annealed at 900°C. The XRD patterns could be refined by using P42/ space group with typical lattice parameters a = b = 4.7322 Å and c = 3.1848 Å. The as milled powders obtained from both the vials exhibit room temperature ferromagnetism (FM) without any transition element doping. However upon annealing, the FM was destroyed in one of the samples. The observed FM is explained in terms of oxygen vacancy and defects induced electrons and exchange interaction between them. The ferromagnetic transition temperature obtained from the temperature variation of magnetization was found to be 915 K. The initial magnetization data could be analyzed in terms of bound magnetic polaron model. The resonance field shift in electron spin resonance spectrum is explained in terms of observed ferromagnetism. [ABSTRACT FROM AUTHOR]

Co-doped SnO based diluted magnetic oxides were prepared by mechanical alloying followed by high temperature annealing. XRD patterns could be refined to P4/mnm space group with typical lattice parameters a= b=4.733 Å and c=3.184 Å. Presence of a minor spinel structure based impurity phase was detected. Room temperature ferromagnetism was observed with a maximum saturation magnetization of 5.9 emu/g for SnCoO sample. The magnetization data after subtracting the contribution from the impurity phase could be analyzed based on a bound magnetic polaron model. Temperature variation of magnetization exhibits clear paramagnetic to ferromagnetic transition with a maximum T of 640 K for 2 at% Co-doped sample. Susceptibility in paramagnetic region could be fitted to the Curie-Weiss law. [ABSTRACT FROM AUTHOR]

Nanocrystalline samples of pure and 2 at% Co-doped SnO2 was prepared by a co-precipitate technique with a crystallite size of the order 10 nm. The homogeneity and single-phase nature of the sample was confirmed by using various characterization techniques, such as X-ray diffraction, transmission electron microscope, and Fourier infrared spectroscopy. Magnetization measurement shows a signature of room temperature ferromagnetism. The reduction in magnetization with decrease in crystalline size has been explained as a result of restriction in the range of bound magnetic polaron interaction. The samples prepared under nitrogen gas environment exhibit improvement in ferromagnetic behavior and enhanced electrical conductivity. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline Sn1−x Ni x O2 samples were prepared in single-phase form for and 0.07 and were characterized using several experimental techniques. Room-temperature ferromagnetism with transition temperature, , as high as 770 K was observed from the temperature variation of magnetization measurements. Nanoparticles of uniform crystalline phase and composition were identified from the transmission electron microscope images. The initial magnetization curves recorded at 80 and 300 K for both samples could be analyzed based on the bound magnetic polaron (BMP) model, where the size of the BMP is found to increase with temperature. The magnitude of electrical resistivity is found to decrease with doping, and its temperature dependence could be explained based on the variable range hopping mechanism. [Copyright &y& Elsevier]

Abstract: Co doped bulk SnO2 based diluted magnetic semiconductors were prepared in single-phase form up to 10% of doping. The magnetic properties were studied from magnetization and electron spin resonance measurements. The magnetization of the 2% doped sample annealed under N2 gas atmosphere exhibited a saturation magnetization of /Co ion and it could be analysed based on the Brillouin function model by taking into account the ferromagnetic contribution. The magnetization versus field (–) curves for the other samples recorded at three different temperatures could be analyzed based on the bound magnetic polaron model. The variation of the spontaneous moment of the bound magnetic polaron with temperature and doping concentration is explained in detail. [Copyright &y& Elsevier]