Magnetotransport properties of magnetite-hematite composite oxides

We have studied transport properties of composite oxides composed of ferrimagnetic conductor Fe 3O 4 (magnetite) and insulating α-Fe 2O 3 (hematite) at room temperature. High-density composite oxides with different Fe 3O 4/Fe 2O 3 ratios were successfully synthesized by melting Fe 2O 3 rods at high temperatures in ambient atmosphere. Transport properties of Fe 3O 4-Fe 2O 3 composites were measured and compared with that of Fe 3O 4 single crystals. As the ratio of the insulating Fe 2O 3 concentration to the conductive Fe 3O 4 one increases, the longitudinal resistivity increases exponentially, while the Seebeck coefficient decreases linearly. The contrasting dependences of electric and thermoelectric transports on the insulating Fe 2O 3 concentration indicate that the thermoelectric transport is less susceptible to disorder effects than electric ones. The measurement of the Hall effect shows that the anomalous Hall effect due to the ferrimagnetic Fe 3O 4 phase is clearly observed in the composite oxides. In line with the resistivity increase with the Fe 2O 3 concentration, the anomalous Hall resistivity increases, following the universal scaling relation established in the dirty limit. The anomalous Nernst effect due to the Fe 3O 4 phase is also observed in the composite oxides. The anomalous Nernst coefficient decreases with increasing Fe 2O 3 concentration, and the decrease is found to be related to the anomalous Hall effect through the Mott relation.We have studied transport properties of composite oxides composed of ferrimagnetic conductor Fe 3O 4 (magnetite) and insulating α-Fe 2O 3 (hematite) at room temperature. High-density composite oxides with different Fe 3O 4/Fe 2O 3 ratios were successfully synthesized by melting Fe 2O 3 rods at high temperatures in ambient atmosphere. Transport properties of Fe 3O 4-Fe 2O 3 composites were measured and compared with that of Fe 3O 4 single crystals. As the ratio of the insulating Fe 2O 3 concentration to the conductive Fe 3O 4 one increases, the longitudinal resistivity increases exponentially, while the Seebeck coefficient decreases linearly. The contrasting dependences of electric and thermoelectric transports on the insulating Fe 2O 3 concentration indicate that the thermoelectric transport is less susceptible to disorder effects than electric ones. The measurement of the Hall effect shows that the anomalous Hall effect due to the ferrim...