Room-temperature ferromagnetism and anomalous electrical transport in Fe-doped ITO thin films

Here, we report the structural, optoelectronic, and magnetic properties of sputtered Fe-doped ITO thin films. X-ray diffraction analysis confirms the formation of a single-phase cubic bixbyite structure, indicating effective diffusion and substitution of Fe ions into the ITO lattice without evidence of secondary phases. The incorporation of Fe ions introduces localized magnetic moments into the ITO host matrix. Increasing the annealing temperature reduces the defect density and enhances the optical transmittance, consistent with the observed decrease in Urbach energy. Temperature-dependent resistivity measurements reveal an anomalous semiconducting behavior strongly influenced by the annealing conditions. Magnetic characterization demonstrates the coexistence of paramagnetic and ferromagnetic contributions, with room temperature ferromagnetism reaching a saturation magnetization up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 0.64 emu g <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> (1.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> /Fe) after annealing at 400 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mo/> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> C. The observed ferromagnetism in the Fe-doped ITO samples is attributed to oxygen vacancies, which promote the formation of bound magnetic polarons near Fe ions. The resistivity-temperature curve shows a Kondo-like upturn at low temperatures, suggesting scattering of conduction electrons by localized Fe ions. Photocurrent measurements confirm n-type conductivity, which is significantly enhanced upon annealing at 700 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mo/> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> C.