Geometric and Disorder-Type Magnetic Frustration in Ferrimagnetic “114” Ferrites: Role of Diamagnetic Li+ and Zn2+ Cation Substitution

Abstract

The comparative study of the substitution of zinc and lithium for iron in the “114” ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations play a major role in tuning the competition between ferrimagnetism and magnetic frustration in these oxides. The substitution of Li or Zn for Fe in the cubic phase YBaFe4O7 leads to a structural transition to a hexagonal phase YBaFe4−x M x O7, for M = Li (0.30≤x≤0.75) and for M = Zn (0.40≤x≤1.50). It is seen that for low doping values, i.e. x=0.30 (for Li) and x=0.40 (for Zn), these diamagnetic cations induce a strong ferrimagnetic component in the samples, in contrast to the spin-glass behavior of the cubic phase. In all the hexagonal phases, YBaFe4−x M x O7 and CaBaFe4−x M x O7 with M = Li and Zn, it is seen that in the low-doping regime (x∼0.3 to 0.5), the competition between ferrimagnetism and 2D magnetic frustration is dominated by the average valency of iron. In contrast, in the high-doping regime (x∼1.5), the emergence of a spin glass is controlled by the high degree of cationic disorder, irrespective of the iron valency.