Structural and Magnetic Characterization of Mechanically Alloyed (Fe2O3)1−x(Al2O3)x Solid Solutions via Pulsed Neutron Powder Diffraction

Neutron powder diffraction experiments were carried out to characterize mechanochemically synthesized (Fe₂O₃)_1-x(Al₂O₃)_x solid solutions with corundum-type structure, focusing on their lattice and magnetic structures with varying temperature and composition. The neutron diffraction experiments for (Fe₂O₃)_0.5(Al₂O₃)_0.5 in the temperature range between 4 K and 300 K reveal that no significant structural phase transition occurred. The behavior of temperature variation of lattice parameters is different from α-Fe₂O₃ and α-Al₂O₃ and reveals the thermal expansion coefficients of α<i>_a</i> = 5.76(2) × 10^-6 K^-1 and α<i>_c</i> = 6.19(5) × 10^-6 K^-1 between 200 K and 300 K. The room temperature neutron diffraction of (Fe₂O₃)_1-x(Al₂O₃)_x shows a linear decrease in lattice parameters with the aluminum substitution, following Vegard's law, along with a decrease in the magnetic moment, indicating the dilution effect on spin interactions. With the increase in the aluminum substitution from x = 0 to 0.5, the deduced magnetic moment decreases from 2.224 <i>μ</i>_B to 0.862 <i>μ</i>_B.