Magnetic properties of ${\mathrm{In}}_2{\mathrm{O}}_3$ containing ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles

Films of Fe-doped ${\mathrm{In}}_2{\mathrm{O}}_3$ that were deliberately fabricated so they contained ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles were deposited on sapphire substrates by pulsed laser deposition at low oxygen pressure. The concentration of Fe was varied between 1% and 5%, and the effect of including 5% of Sn and vacuum annealing were also investigated. Structural analysis indicated a high concentration of ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles that caused substantial values of the coercive field at room temperature. Transport measurements indicated that the films were metallic, and an anomalous Hall effect was observed for the sample with 5% of Fe. The concentration of nanoparticles was reduced dramatically by the inclusion of 5% of Sn. Magnetic circular dichroism spectra taken in field and at remanence were analyzed to show that the samples had a magnetically polarized defect band located below the conduction band as well as magnetic ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles. The signal from the defect states near the band edge was enhanced by increasing the number of carriers by either including Sn or by annealing in vacuum.

Figure 1

(a) XRD intensities for films with varying percentages of Fe done with a long scan time and plotted logarithmically. (b) SEM scan done at 5 kV of the 5% sample. The dark areas indicate the ${\mathrm{Fe}}_3{\mathrm{O}}_4$.

Figure 2

Fe $K$ edge data for the 5% Fe ${\mathrm{In}}_2{\mathrm{O}}_3$ sample compared to ${\mathrm{Fe}}_3{\mathrm{O}}_4$ magnetite; (a) normalized near edge and (b) ${\mathrm{k}}^2$ weighted EXAFS.

Figure 3

(a) The resistivity plotted as a function of temperature for a 2% Fe film, (b) carrier concentration, and (c) the Hall mobility of the films as a function of Fe concentration.

Figure 4

(a) Hysteresis loops measured at 300 K of ${(\mathrm{In}}_{1-x}{\mathrm{Fe}}_x{)}_2{\mathrm{O}}_3$ with the field in plane (the diamagnetic contribution from the substrate has been subtracted).The inset shows an expanded view of the region around the origin. (b) The saturation magnetization at 5 K and 300 K as a function of the Fe doping level compared with expected magnetization from 85% of Fe in the films in the form of ${\mathrm{Fe}}_3{\mathrm{O}}_4$. (c) The coercive field, $H_c$, at 5 K and 300 K as a function of the measured Fe doping level. (d) ZFC and FC magnetization of ${(\mathrm{In}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_2{\mathrm{O}}_3$ film, taken at 250 Oe, as a function of temperature. (e) Comparison of the hysteresis loops taken for the 5% sample with the field in plane and perpendicular to the plane.

Figure 5

Hall effect measurements of the 5% film measured at 10 K. Raw data are shown in (a), and the result when the linear term is subtracted in (b).

Figure 6

(a) Optical reflection spectra and (b) absorption spectra for ${(\mathrm{In}}_{1-x}{\mathrm{Fe}}_x{)}_2{\mathrm{O}}_3$ thin films with varying Fe content; the band gaps are shown in the inset.

Figure 7

MCD spectra of ${(\mathrm{In}}_{1-x}{\mathrm{Fe}}_x{)}_2{\mathrm{O}}_3$ thin films (a) in an external applied field of 1.8 Tesla, (b) at remanence (in magnetic field of 0 T) measured at RT. The contribution from the substrate was subtracted from the data.

Figure 8

(a) MCD data for a ${(\mathrm{In}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_2{\mathrm{O}}_3$ thin film measured at RT and magnetic field of 1.8 T. The red line represents the experimental value of the imaginary part of the off-diagonal dielectric tensor. The black line is a fit to the contribution from the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles using Maxwell-Garnett theory, while the difference (blue line) is the contribution from the ${\mathrm{In}}_2{\mathrm{O}}_3$ matrix. (b) The values of the volume fraction $f$ corresponding to nanoparticles as computed from the MCD (black line) and the value obtained from EXAFS measurements on the 5% film (red line) plotted against the measured percentage of Fe. (c) Variation in the MCD amplitude at 3.2 eV with Fe content for ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles and the oxide component. The lines in (b) and (c) are to guide the eye. (d) The MCD data for 5% Fe sample at 1.8 T and at remanence.

Figure 9

(a) Variation in the MCD spectrum of ${(\mathrm{In}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_2{\mathrm{O}}_3$ thin films with varying tin content. (b) Variation in the MCD spectra of ${(\mathrm{In}}_{0.95}{\mathrm{Fe}}_{0.05}{)}_2{\mathrm{O}}_3$ thin films with annealing temperature

Figure 10

The MCD loop taken at (a) 2.2 eV and (b) 3.2 eV (note that the reversal occurs because the MCD is negative). The linear background from the substrate has been subtracted.