Enhanced structural and magnetic ordering in as-synthesized Ca doped bismuth iron oxide nanoceramics

Abstract

Calcium (Ca) added bismuth iron oxide (Bi1-xCaxFeO3) nanoparticles are synthesized using sol-gel method and studied under as-synthesized conditions. Calcium (Ca) concentration (x) is varied as 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5. XRD results verify the formation of phase pure BiFeO3 at dopant concentration x = 0.0–0.3. Raman analysis and EDX spectrum also confirm the formation and incorporation of Ca in the lattice. At x = 0.4 and 0.5 peaks corresponding to calcium oxide are observed. With addition of Ca ions in the lattice, strain is induced, resulting in reduced symmetry and increased inhomogeneity in the crystal structure. XPS analysis indicates small number of Fe2+ cations whereas no change in oxygen stoichiometry is observed. Size distribution and surface morphology of nanoparticles is observed using SEM and TEM images. Ca added bismuth iron oxide nanoparticles demonstrate ferromagnetic behavior where saturation magnetization increases from 9.202 emu/g to 21.097 emu/g as x increases from 0.0 to 0.3. This increase in saturation magnetization is accompanied by reduced magnetocrystalline anisotropy. High temperature magnetization curves indicate increase in magnetic ordering temperature from 643.7 K to 697 K. Field-cooled and zero field-cooled curves exhibit magnetic ordering with blocking temperature of ∼89 K under applied field of 500 Oe. P-E loops show high saturation polarization of 3.58 × 10−4 μC/cm2 for Ca concentration of x = 0.3. It is important to mention here that nanoparticles are synthesized without the use of any post thermal treatment.