Influence of nonmagnetic cation substitution on magnetic order temperature in Y-type hexaferrites: Ba_0.5Sr_1.5Zn₂Fe₁₂O₂₂ and Ba_0.5Sr_1.5Zn₂Al_0.08Fe_11.92O₂₂

With a view to the proven multiferroic properties of the title representatives of the Y-type hexaferrites as single crystals we present here a comparative study of their microstructure and magnetic properties for powders. The polycrystalline materials of Ba 0.5 Sr 1.5 Zn 2 Fe 12 O 22 (S1) and its doped with aluminium derivative Ba 0.5 Sr 1.5 Zn 2 Al 0.08 Fe 11.92 O 22 (S2) were synthesized by two different techniques: citric-acid sol-gel auto-combustion and sonochemical co-precipitation. Their atomic-level structure determination was checked by X-ray and neutron diffraction, electron diffraction and imaging methods, and their physical characterization was carried out by magnetometry. SEM images show that the microstructure strongly depends on the method of synthesis: non-uniform hexagonal grans are formed in case of auto-combustion whereas particles of nearly perfect hexagonal shape are observed in case of sonochemical co-precipitation. With lowering the temperature to 5 K several magnetic phase transitions were observed, more clearly pronounced in S2 powders. Neutron diffraction data in vicinity and above room temperature help in revealing the effect of magnetic dilution on the observed magnetic properties.