Impact of evolution of structural defects on the ferromagnetic and electrical properties of laser deposited Indium-doped SnO2 thin films

Impact of non-magnetic cationic-substitution on the evolution of structural defects and correlated ferromagnetic and electrical properties are investigated in series of pulsed laser deposited Sn_1-xIn_xO₂ (0.0 ≤ x ≤ 0.12) thin films. Beyond the nominal doping concentration of 2 at.% (i.e. x > 0.02), Indium (In)-doped SnO₂ film switches to exhibit from n-type to p-type electrical conductivity and simultaneously the magnetization (M_S) as well as the Curie temperature (T_C) of the films increase significantly. Estimated values of ‘M_S’ and ‘T_C’ are found to achieve as large as 15.21 emu/cm³ and 540 K respectively when In-doping concentration approaches towards x = 0.08 and afterwards tend to decrease abruptly. Various spectroscopic techniques including Positron Annihilation Lifetime Spectroscopy (PALS) have detected the existence of Sn vacancy (V_Sn) defects within Sn_1-xIn_xO₂ films arise as the effect of In-substitution at Sn site (In_Sn) under O-rich atmosphere. The estimated positron lifetimes and the increase of line-shape S-parameter confirm the rise of V_Sn defects which serve as the major source of magnetic moments in non-magnetic host SnO₂. Besides, In_Sn defects introduce excess holes within SnO₂ lattice and thereby the magnetic spin-spin RKKY interaction between near-by V_Sn defects are mediated ferromagetically through the localized holes. For x > 0.08, stabilization of various donor-type defects such as Sn interstitial (Sn_i), indium interstitial (In_i) actually compensates the acceptors that leads to reduce the effective hole density consequently diminishing the strength of ferromagnetism within SnO₂. Hence, tuning of such ferromagnetic and semiconducting properties through non-magnetic cationic substitution in transparent conducting oxides can be very promising in the field of next-generation spintronics.