Dopant Spin States and Magnetic Interactions in Transition Metal (Fe 3+ )-Doped Semiconductor Nanoparticles: An EMR and Magnetometric Study

In this work, electron magnetic resonance (EMR) spectroscopy and magnetometry studies were employed to investigate the origin of the observed room-temperature ferromagnetism in chemically synthesized Sn1−x Fe x O2 powders. EMR data clearly established the presence of two different types of signals due to the incorporated Fe ions: paramagnetic spectra due to isolated Fe3+ ions and broad ferromagnetic resonance (FMR) spectra due to magnetically coupled Fe3+ dopant ions. EMR data analysis and simulation suggested the presence of high-spin (S = 5/2) Fe3+ ions incorporated into the SnO2 host lattice both at substitutional and at interstitial sites. The FMR signal intensity and the saturation magnetization M s of the ferromagnetic component increased with increasing Fe concentration. For Sn0.953Fe0.047O2 samples, well-defined EMR spectra revealing FMRs were observed only for samples prepared in the 350–600°C range, whereas for samples prepared at higher annealing temperatures up to 900°C, the FMRs and saturation magnetization were vanished due to diffusion and eventual expulsion of the Fe ions from the nanoparticles, in agreement with data obtained from Raman and X-ray photoelectron spectroscopy.