[Paper Review] Room temperature ferromagnetism in transparent and conducting Mn-doped $SnO_{2}$ thin films

Sushant Gupta, V. Ganesan+3 more|arXiv (Cornell University)|Sep 8, 2017

ZnO doping and properties76 references3 citations

TL;DR

This study demonstrates room-temperature ferromagnetism in transparent, conducting Mn-doped SnO₂ thin films fabricated via spray pyrolysis. The films exhibit high electrical conductivity, visible-range transmittance (50–65%), and a Curie temperature exceeding 350 K, indicating potential for oxide-based spintronic devices without secondary phase contributions.

ABSTRACT

The magnetization as a function of magnetic field showed hysteretic behavior at room temperature. According to the temperature dependence of the magnetization, the Curie temperature $(T_{C})$ is higher than 350 K. Ferromagnetic Mn-doped tin oxide thin films exhibited low electrical resistivity and high optical transmittance in the visible region (400-800 nm). The coexistence of ferromagnetism, high visible transparency and high electrical conductivity in the Mn-doped $SnO_{2}$ films is expected to be a desirable trait for spintronics devices.

Motivation & Objective

• To achieve room-temperature ferromagnetism in transparent and conducting Mn-doped SnO₂ thin films.
• To investigate the coexistence of ferromagnetism, high electrical conductivity, and optical transparency in SnO₂-based dilute magnetic semiconductors.
• To rule out secondary phases as the origin of observed ferromagnetism through structural and magnetic characterization.
• To correlate defect chemistry, particularly H⁺ defects, with electrical and magnetic properties in doped SnO₂ films.

Proposed method

• Spray pyrolysis was used to deposit Mn-doped SnO₂ thin films on glass substrates at 450 °C with Mn concentrations ranging from 0 to 15 at.%
• X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to confirm the tetragonal rutile phase and absence of secondary phases.
• The Williamson-Hall method was applied to analyze crystallite size and microstrain from XRD data.
• Electrical resistivity and Hall measurements were conducted to determine carrier concentration and mobility, identifying ionized impurity scattering by H⁺ defects.
• Optical bandgap was calculated using the Tauc plot method from absorption coefficient data.
• Magnetic hysteresis loops were measured at room temperature and as a function of temperature to determine Curie temperature (T_C) and ferromagnetic behavior.

Experimental results

Research questions

• RQ1 Can Mn doping induce stable, high-temperature ferromagnetism in transparent SnO₂ thin films?
• RQ2 What is the origin of ferromagnetism in Mn-doped SnO₂—defect-mediated mechanisms or secondary phases?
• RQ3 How does Mn doping affect the electrical conductivity and optical transparency of SnO₂ films?
• RQ4 What is the Curie temperature of Mn-doped SnO₂ thin films, and does it exceed room temperature?
• RQ5 To what extent do H⁺ defects influence the electrical and magnetic properties of the doped films?

Key findings

• Mn-doped SnO₂ thin films exhibited clear magnetic hysteresis loops at room temperature, confirming ferromagnetic behavior.
• The Curie temperature (T_C) of the films was found to be higher than 350 K, indicating robust room-temperature ferromagnetism.
• Electrical resistivity was low, with carrier concentration and mobility consistent with n-type conduction dominated by ionized impurity scattering from H⁺ defects.
• Optical transmittance in the visible range (400–800 nm) ranged from 50% to 65%, demonstrating high transparency.
• XRD and TEM analyses confirmed the absence of secondary phases such as MnO, Mn₂O₃, Mn₃O₄, or SnMn₂O₄, ruling out phase-induced ferromagnetism.
• A redshift in the optical bandgap was observed with increasing Mn doping, attributed to strong exchange interactions between sp carriers and Mn d-electrons.