Preparation of nano-sized Al-substituted yttrium iron garnets by the mechanochemical method and investigation of their magnetic properties

摘要

The polycrystalline Y_3Fe_(5-x)Al_xO_(12) compounds with x = 0.5, 1.0, 1.5 and 2.0 were prepared by the mechanochemical method. The samples were milled for 40 h in a high-energy planetary mill and then calcined at different temperatures from 1300 to 1100 ℃. The minimum calcination temperature to get a single phase garnet decreases by increasing Al concentration. X-ray diffraction patterns reveal that the structures of nano-powders are bcc and the garnet phase has been obtained after calcining. Also, the lattice constant of the samples decreases by increasing Al concentration, which is discussed based on the substitution of smaller aluminum ions instead of iron ions. The average crystallite sizes are in the range 24-35 nm using Scherrer's formula. The Curie temperature of single phase samples was found to decrease by increasing Al concentration, which can be discussed upon the reduction of magnetic interactions per magnetic ion. When more Al~(3+) is added, the magnetization is reduced because of the reduction of superexchange interactions in crystal lattice.