AyB1−yCxFe2−xO4 (C=Ho,Gd,Al) ferrite powders have been synthesized by the sol-gel combustion route. The X-ray diffraction of the CoHoxFe2−xO4 (x = 0~0.08) results indicated the compositions of single-phase cubic ferrites. The saturation magnetisation of CoHoxFe2−xO4 decreased by the Ho3+ ions, and the coercivity increased initially and then decreased with the increase of the calcination temperature. The Mössbauer spectra indicated that CoHoxFe2−xO4 displays a ferrimagnetic behaviour with two normal split Zeeman sextets. The magnetic hyperfine field tends to decrease by Ho3+ substitution owing to the decrease of the A–B super-exchange by the paramagnetic rare earth Ho3+ ions. The value of the quadrupole shift was very small in the CoHoxFe2−xO4 specimens, indicating that the symmetry of the electric field around the nucleus is good in the cobalt ferrites. The absorption area of the Mössbauer spectra changed with increasing Ho3+ substitution, indicating that the substitution influences the fraction of iron ions at tetrahedral A and octahedral B sites. The X-ray diffraction of Mg0.5Zn0.5CxFe2−xO4(C=Gd,Al) results confirmed the compositions of single-phase cubic ferrites. The variation of the average crystalline size and lattice constant are related to the doping of gadolinium ions and aluminum ions. With increasing gadolinium ions and aluminum ions, the coercivity increased and the saturation magnetization underwent a significant change. The saturation magnetization of AlMg0.5Zn0.5FeO4 ferrite reached a minimum value (MS= 1.94 mu/g). The sample exhibited ferrimagnetic and paramagnetic character with the replacement with Gd3+ ions, that sample exhibited paramagnetic character with the replacement with Al3+ ions, and the isomer shift values indicated that iron is in the form of Fe3+ ions.

Homohelical chains with magnetite like valence distribution exhibit ferrimagnetism, canted antiferromagnetism, spin-flop and field-induced SCM like behaviours.

LiFePO4 takes advantage of structure stability, safety and environmental friendliness, and has been favored by the majority of scientific researchers. In order to further improve the properties of LiFePO4, AO-type metal oxides (MgO and ZnO) and LiFePO4/C composites were successfully prepared by a two-step sol-gel method. The effects of AO-type metal oxides (MgO and ZnO) on LiFePO4/C composites were studied. TG, XRD, FTIR, SEM and VSM analysis showed that the final product of the MgO and LiFePO4/C composite was about 70.5% of the total mass of the precursor; the complete main diffraction peak of LiFePO4 and MgO can be found without obvious impurity at the diffraction peak; there is good micro granularity and dispersion; the particle size is mainly 300 nm; the saturation magnetization (Ms), the residual magnetization (Mr) and the area of hysteresis loop are increased with the increase in MgO content; and the maximum Ms is 11.11 emu/g. The final product of ZnO and LiFePO4/C composites is about 69% of the total mass of precursors; the complete main diffraction peak of LiFePO4 and ZnO can be found without obvious impurity at the diffraction peak; there is good micro granularity and dispersion; the particle size is mainly 400 nm; and the coercivity (Hc) first slightly increases and then gradually decreases with the increase of zinc oxide.

No abstract