We report a microwave-combustion synthesis and structure-related physical properties of Ni_0.4Zn_0.6−xCr_xFe₂O₄ (0.0 ≤ x ≤ 0.6) nanocrystals in a study of effects by substitution among cations with different oxidation states, Cr³⁺ for Zn²⁺. High-quality nanocrystals with an average particle size of 26 – 33 nm and crystallite size ranged in 23 - 32 nm are revealed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Structural properties and cationic redistribution are studied by the XRD Rietveld analysis implying different preferences of Zn²⁺ and Cr³⁺ ions to occupy the tetrahedral and octahedral sites, respectively. Further characterization for the characteristic IR absorption bands, ionic valence states, chemical compositions and morphology have been performed by employing the Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electron dispersive X-ray (SEM-EDX …