Investigation of local geometrical structure, electronic state and magnetic properties of PLD grown Ni doped SnO₂ thin films

Highlights: • Ni doped SnO₂ thin films were deposited on Si substrate (001) by PLD technique. • NEXAFS at Ni L_3,2 edges confirmed that the Ni ions exist in high spin divalent ground state. • The UHV assisted growth condition created a favorable condition for oxygen non-stoichiometry. • A significant modification have be observed in the surface morphology. • Magnetic behavior seems to be more relevant to the formation of VO²⁺ at the surfaces. - Abstract: We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO₂ thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO₂ rutile lattice structure with P4₂/mnm space group. The inclusion of Ni ions into SnO₂ matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn⁴⁺ (SnO₂) to Sn³⁺ (Sn₂O₃), these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L_3,2 and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that Ni doped SnO₂ films displayed ferromagnetic (FM) signal, and there was no significant difference in the saturation moments even with increase in the Ni content. Hence, the similarity in the observed magnetic behavior of the films seems relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed in the light of spin-split impurity band percolation mechanism.