Sm2Bi2Fe4O12 ferromagnetic semiconductor

Samples of Sm2Bi2Fe4O12 were solid reacted. Structural characterization through the X-ray diffraction technique evidences that the synthesized ceramic crystallizes in orthorhombic structures (Pnma, #62 space group). Micrographs reveal the granular and densified feature on the surface and inside of the samples. Two micrometric and submicrometric grain sizes were mostly observed. X-ray energy dispersion spectra allowed establishing the stoichiometric composition suggested by the chemical formula of the compound. The electrical behavior was studied by means of I-V curves and electrical permittivity as a function of temperature. Results reveal semiconductor-like behaviors with strong influences on the polycrystalline character of the material and a Maxwell-Wagner-type dielectric trend. Diffuse reflectance spectra corroborate the semiconductor feature with optical band gap Eg=2.62 eV. Temperature-dependent magnetization curves for applied fields of 500, 2000 and 10000 Oe show a ferromagnetic characteristic, with strong evidence of disorder causing magnetic irreversibility between the Zero Field Cooling and Field Cooled measurement procedures. The ferromagnetic type ordering was established from the hysteretic character of magnetization curves measured at 50, 200 and 300 K temperatures. Ab-initio calculations of the electronic density of states show the occurrence of a mean semiconducting gap of 2.38 eV produced by hybridizations of orbitals of the nonmetallic cations with the 2p oxygen electrons. 3d-Fe orbitals are responsible by the strong asymmetry between the spin-up and -down polarized states, which gives rise to a high magnetic moment. The increase in applied pressure and temperature produces substantial changes in the thermophysical properties of the material. At low temperatures, the specific heat reveals a trend to the Dulong-Petit limit, which converges to 490.2 J/mol.K. In this temperature regime, changes occur in all the thermophysical properties studied because of the effect of pressure and temperature on the wave behavior of the crystal lattice. At higher temperatures, a strong variation in Debye temperature and divergence between the behaviors of entropy, thermal expansion and Grüneisen parameter for different applied pressures are observed. Based on these results, the material is classified as a ferromagnetic semiconductor with low coercive field and medium saturation magnetization that would have eventual technological implications in the spintronic industry.
To see the full article, search DOI: 10.1039/D0TC02935A