Structural and magnetic study of Al3+ doped Ni0.75Zn0.25Fe2−xAlxO4 nanoferrites

•Grain size reduction with Al3+ substitution.•Preferred occupancy of Al3+ at B site for higher Al3+ content.•Reduction in Ms, Tc, and hyperfine field with increasing Al3+ content.•Size dependent variation in coercivity.•Changes in isomer shift due to competing effect of volume and substitution.

Nanostructured Al3+ doped Ni0.75Zn0.25Fe2−xAlxO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) ferrites were synthesized via the wet chemical method. X-ray diffraction, transmission electron microscopy, and magnetization measurements have been used to investigate the structural and magnetic properties of spinel ferrites calcined at 950 °C. With the doping of Al3+, the particle size of Ni0.75Zn0.25Fe2−xAlxO4 first increased to 47 nm at x = 0.4 and then decreased down to 37 nm at x = 1. The main two absorption bands in IR spectra were observed around 600 cm−1 and 400 cm−1 corresponding to stretching vibration of tetrahedral and octahedral group Fe3+–O2−. Saturation magnetization and hyperfine field values decreased linearly with Al3+ due to magnetic dilution and the relative strengths of Fe–O–Me (Me = Fe, Ni, Zn, and Al) superexchanges. The coercive field showed an inverse dependence on ferrite particle size with minimum value of 82 Oe for x = 0.4. A continuous drop in Curie temperature was observed with the Al3+ substitution. From the Mossbauer spectral analysis and X-ray diffraction analysis, it is deduced that Al3+ for x < 0.4 has no obvious preference for either tetrahedral or octahedral site but has a greater preference for the B site for x > 0.4. In nutshell the study presents detailed structural and magnetic, and Mossbauer analysis of Ni0.75Zn0.25Fe2−xAlxO4 ferrites.

Graphical abstractHyperfine field of individual sites (inset) and weighted average hyperfine field as a function of Al3+ content for Ni0.75Zn0.25Fe2−xAlxO4.Figure optionsDownload full-size imageDownload as PowerPoint slide