Synthesis, electronic transport and optical properties of Si:α-Fe₂O₃ single crystals

Abstract

We report the synthesis of silicon-doped hematite (Si:a-Fe 2 O 3 ) single crystals via chemical vapor transport, with Si incorporation on the order of 10 19 cm À3. The conductivity, Seebeck and Hall effect were measured in the basal plane between 200 and 400 K. Distinct differences in electron transport were observed above and below the magnetic transition temperature of hematite at B265 K (the Morin transition, T M ). Above 265 K, transport was found to agree with the adiabatic small-polaron model, the conductivity was characterized by an activation energy of B100 meV and the Hall effect was dominated by the weak ferromagnetism of the material. A room temperature electron drift mobility of B10 À2 cm 2 V À1 s À1was estimated. Below T M , the activation energy increased to B160 meV and a conventional Hall coefficient could be determined. In this regime, the Hall coefficient was negative and the corresponding Hall mobility was temperature-independent with a value of B10 À1 cm 2 V À1 s À1. Seebeck coefficient measurements indicated that the silicon donors were fully ionized in the temperature range studied. Finally, we observed a broad infrared absorption upon doping and tentatively assign the feature at B0.8 eV to photon-assisted small-polaron hops. These results are discussed in the context of existing hematite transport studies.

Control of spin‐reorientation transition in (0001) oriented α‐Fe2O3 thin film by external magnetic field and temperature

“…It was found that with increasing temperature H SR decreases linearly. Similar values of H SR were observed by Rettie et al using anomalous hall effect measurement below the transition temperature T SR . However, above T SR , no spin reorientation was observed.…”

Experimental effects on IR reflectance spectra: particle size and morphology

“…The gold coating surface has high reflectivity yet is somewhat matte resulting in a ~91% Lambertian component. [7][8][9][10][11][12][13] A beamsteering mirror located within the sphere can be pointed down at the sample port, up at a fixed reference point, or at any angle on the sphere's front wall. Due to the horizontal position of the sample port at the bottom of the sphere, a glass cover is not necessary, which therefore removes the introduction of errors associated with the glass.…”

“…We have further applied the method to various samples such as hematite and investigated the difference in reflectance between visible and near infrared regions and mid-infrared regions. [9][10] Various spectral features can be observed in the infrared region depending on the particle size: the data presented in this paper are used to study in particular three types of spectral features: reststrahlen bands, Christiansen features, and transparency peaks. Christiansen minima have little to no absorption or scattering therefore radiation is able to pass through the sample, causing minimal to no reflectance, i.e.…”

“…[1][2][3][4][5] Even sample preparation can influence the reflectance spectra. [6][7][8][9][10][11] The optical constant n determines the phase velocity of the light going through the sample whereas k measures the loss of light, i.e. k is proportional to the absorption coefficient.…”

“…[6][7][8][9][10][11] This method was developed so as to allow us to take a commercially-available integrating sphere and develop techniques to measure infrared standards and other common materials. The measurements have been ' i vetted against visible near-infrared measurement in wavelength domains that overlap.…”