Microstructure and Magnetic Properties of Sn1 − x Ni x O2 Thin Films Prepared by Flash Evaporation Technique

An effort was made to develop semiconductor oxide-based room temperature dilute magnetic semiconductor (DMS) thin films based on wide band gap and transparent host lattice with transition metal substitution. The Sn $_{\mathrm {1}-x}$ Ni $_{x}\textit {O}_{\mathrm {2}}$ ( $x\,= \mathrm {0.00, 0.03, 0.05, 0.07, 0.10, and \,0.15}$ ) thin film samples were prepared on glass substrates by flash evaporation technique. All the samples were shown single phase crystalline rutile structure of host SnO $_{\mathrm {2}}$ with dominant (110) orientation. The Ni substitution promotes reduction of average crystallite size in SnO $_{\mathrm {2}}$ as evidenced from the reduction of crystallite size from 40 (SnO $_{\mathrm {2}}$ ) to 20 nm (Sn $_{\mathrm {0.85}}$ Ni $_{\mathrm {0.15}}\textit {O}_{\mathrm {2}}$ ). In the energy dispersive spectra as well as X-ray photoelectron spectra of all the samples show, the chemical compositions are close to stoichiometric with noticeable oxygen deficiency. The crystalline films were formed by coalescence of oval-shaped polycrystalline particles of 100 nm size as evidenced from the electron micrographs. The energy band gap of DMS films decreases from 4 (SnO $_{\mathrm {2}}$ ) to 3.8 eV (x $=$ 0.05) with increase of Ni content. The magnetic hysteresis loops of all the samples at room temperature show soft ferromagnetic nature except for SnO $_{\mathrm {2}}$ film. The SnO $_{\mathrm {2}}$ films show diamagnetic nature and it converts into ferromagnetic upon substitution of 3 % Sn $^{\mathrm {4+}}$ by Ni $^{\mathrm {2+}}$ . The robust intrinsic ferromagnetism (saturation magnetization, 21 emu/cm $^{\mathrm {3}}$ ). Further increase of Ni content weakens ferromagnetic strength due to Ni-O antiferromagnetic interactions among the nearest neighbour Ni ions via O $^{\mathrm {2-}}$ ions. The observed magnetic properties were best described by bound magnetic polarons model.