Size, surface structure, and doping effects on ferromagnetism in SnO2

Abstract

The effects of crystallite size, surface structure, and dopants on the magnetic properties of semiconducting oxides are highly controversial. In this work, Fe:SnO 2 nanoparticles were prepared by four wet-chemical methods, with Fe concentration varying from 0-20%. Samples were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Analysis confirmed pure single-phase cassiterite with a crystallite size of 2.6 ± 0.1 nm that decreased with increasing Fe%. Fe concentration was confirmed from XPS studies, with Fe ions in the 3+ oxidation state. Pure SnO 2 showed highly reproducible weak magnetization that varied significantly with synthesis method. Interestingly, doping SnO 2 with Fe<2.5% produced enhanced magnetic moments in all syntheses; the maximum of 1.6x10 -4 µ B /Fe ion at 0.1% Fe doping was much larger than the 2.6x10 -6 µ B /Fe ion of pure Fe oxide nanoparticles synthesized under similar conditions. At Fe≥2.5%, the magnetic moment was significantly reduced. This work shows that (i) pure SnO 2 can produce an intrinsic ferromagnetic behavior that varies with differences in surface structure, (ii) very low Fe doping results in high magnetic moments, (iii) higher Fe doping reduces magnetic moment and destroys ferromagnetism, and (iv) there is an interesting correlation between changes in magnetic moment, band gap, and lattice parameters. These results support the possibility that the observed ferromagnetism in SnO 2 might be influenced by modification of the electronic structure by dopant, size, and surface structure. Introduction:

A Review of EPR Studies on Magnetization of Nanoparticles of Dilute Magnetic Semiconductors Doped by Transition-Metal Ions

“…The dependence of saturation magnetization on the number of oxygen vacancies was reported, in particular, in [28]. Oxygen vacancies on the surface of nanoparticles induce ferromagnetism even in undoped oxides [29][30][31]. As a modification of this approach, there are proposed:…”

Investigations of optoelectronic properties in DMS SnO2 nanoparticles

“…Tin dioxide (SnO 2 ) is an n-type semiconductor with a wide band gap of 3.6 eV (unit cell parameters a = 4.737 Å and c = 3.185 Å and its space group is P42/mmm) has potential application in photoactive system, liquid crystal display transistors, gas sensors, ferroelectric transparent thin film transistors, transparent conducting electrodes, rechargeable lithium batteries, optoelectronic devices, catalyst and spintronic devices [1][2][3][4]. The promising applications of SnO 2 in the spintronics have attracted the researchers for the study of room temperature ferromagnetism in SnO 2 based DMS materials which uses the spin of the particles in addition to their charges.…”

Effect of Mn doping on structural, optical and magnetic properties of SnO2 nanoparticles

“…Unpaired electrons can be trapped in those oxygen vacancies and their spins can polarize together via exchange interactions and lead to ferromagnetic order in SnO 2 nanoparticles [35]. As the strength of externally applied magnetic field is increased the magnetic susceptibility continuously increases for Mn doped SnO 2 [32,[35][36][37][38][39][40][41][42]. The graphs illustrates that as the Mn dopants concentration increases the particles becomes more aligned in the direction of applied magnetic field as the net magnetic moment increases after Mn doping.…”

“…The coercivity and positive susceptibility may be associated with the exchange coupling of the spins of electrons trapped in oxygen vacancies (V o ), which are mainly present on the surface of the SnO 2 nanoparticles and the surface defects created during synthesis process as evident from PL spectra also. The literature reveals that these oxygen vacancies basically located on the particle surface are considered to play a key role for the paramagnetism and ferromagnetism in nanosized SnO 2 [35][36][37][38][39][40][41]. Unpaired electrons can be trapped in those oxygen vacancies and their spins can polarize together via exchange interactions and lead to ferromagnetic order in SnO 2 nanoparticles [35].…”