Physical properties of doped multiferroic GaFeO3

Gallium iron oxide (GaFeO3) is a member of a multiferroic family which exhibits ferrimagnetic and piezoelectric properties below room temperature. The physical properties of GaFeO3 are strongly dependent on the distribution of cations within the structure. GaFe1-xMnxO3 polycrystalline materials have been prepared by a solid state reaction (SR) and by a sol-gel (SG) methods. Also, GaFe1-xCrxO3 was prepared by solid state reaction. The maximum Mn content amounts to 10 and 40 % for SR and SG preparation, respectively, while the maximum Cr amount is 15%. All compounds in these composition ranges crystallize in space group P c 21 n derived from Rietveld refinement of X-ray powder patterns. The gradual incorporation of manganese and chromium are accompanied by a decrease in the cell volume. The Curie temperature (TC) for GaFeO3 (SR) is about 225 K and increases up to above room temperature when the temperature of preparation is decreased from 1300°C to 700°C. With increasing Mn or Cr contents the transition temperatures as well as the coercive field decrease. Dielectric investigations revealed a temperature independent anomaly at around 250 K with frequency dispersion of dielectric constant for Mn doped samples prepared by both methods accompanied by lattice parameters anomaly at the same temperature without change in crystal structure. A combined neutron and Mössbauer data analysis has led to the determination of site assignment and the occupancies. The ordering of Ga and Fe cations depends on the Mn substitution. Below the magnetic transition temperature a ferrimagnetic order with a propagation vector K = 0 was derived from neutron powder diffraction data. The Fe3+ magnetic moments are ordered along the c-axis with small components along a and b. The magnetic structure does not alter for Mn doped GaFeO3 but the magnetic moment decreases as the amount of Mn increases