Low temperature photoluminescence and optical absorption studies on 200MeV Ag+15 ion irradiated Co-implanted ZnO thin films were studied. The Co clusters present in as implanted samples were observed to be dissolved using 200MeV Ag+15 ion irradiation with a fluence of 1×1012ions∕cm2. The photoluminescence spectrum of pure ZnO thin film was characterized by the I4 peak due to the neutral donor bound excitons and the broad green emission. The Co-doped ZnO films show three sharp levels and two shoulders corresponding to 3t2g and 2eg levels of crystal field splitted Co d orbitals, respectively. The ultraviolet-visible absorption spectroscopy also shows the systematic variation of band gap after 200MeV Ag+15 ion irradiation.

Electronic structures of LaFe1−xNixO3 (x⩽0.6) have been studied by x-ray absorption near edge structure spectra of OK, FeL2,3 and LaM4,5 edges. Upon substitution of Ni at Fe site in LaFeO3, the OK-edge spectra show a feature about 2.0eV lower than that of LaFeO3. This feature is growing as the concentration of Ni is increasing. This is consistent with our resistivity data which show that the resistivity decreases very fast with Ni substitution from GΩcm for LaFeO3 to a few mΩcm for the sample with 60% Ni substitution. The resistivity data have been fitted with a variable-range hopping model and it is found that the gap parameter reduces from 2eV to 2.1meV with the Ni substitution. This gap parameter decreases very systematically with the increase in Ni concentration. The structural analysis of these samples shows that they have single-phase orthorhombic structure with space-group Pnma in the studied range (0⩽x⩽0.6). The study of FeL2,3-edge structures confirm the trivalent state of Fe. The observed features have been explained on the basis of charge-carrier doping in LaFeO3. The disorder-induced localization is found to effectively control the resistivity behavior.

Structural, electrical resistivity, and magnetization properties of 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films are presented. The structural studies show the presence of Co clusters whose size is found to increase with increase of Co implantation. The implanted films were irradiated with 200-MeV Ag+15 ions to fluence of 1×1012ions∕cm2. The Co clusters on irradiation dissolve in the ZnO matrix. The electrical resistivity of the irradiated samples is lowered to half. The magnetization hysteresis measurements show ferromagnetic behavior at 300K, and the coercive field increases with the Co implantation. The ferromagnetism at room temperature is confirmed by magnetic force microscopy measurements. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.

The effect of swift heavy ion ͑SHI͒ irradiation ͑190 MeV Ag͒ on structural, electrical transport and magnetic properties of epitaxial magnetite ͑Fe 3 O 4 ͒ thin films ͑thickness ϳ70 nm͒ grown on MgO͗100͘ oriented substrate have been investigated. The x-ray diffraction shows that at low fluence values up to 5 ϫ 10 11 ions/ cm 2 , the strain in the films is relaxed, whereas, at higher fluence range 1 ϫ 10 12 -1 ϫ 10 13 ions/ cm 2 , the epitaxial relationship with the substrate is lost along with a phase transformation from magnetite to more oxidized magnetite phase ͑i.e., maghemite͒. The Verwey transition temperature measured by electrical transport is found to increase from 109 to 117 K with the low fluence SHI irradiation, which is related to the irradiation induced strain relaxation and structural modifications. At higher fluences the system did not show Verwey transition and the resistance is also increased. The similar results were obtained by magnetization studies. The observed magnetization at 1 T field is increased at low fluence suggesting the reduction of areas with frustrated exchange interactions associated with the cationic arrangement at the anti phase boundaries. At higher fluences it decreases monotonically, indicating the emergence of other phases. The observed modifications are explained on the basis of structural strain and disorder induced by swift heavy ions, which lead to modification of the interionic Coulomb potential at octahedral sublattices and bandwidth in this system.

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