I have synthesized Ni-Cu-Zn spinel ferrites via the solid-state method and partially substituted Fe³⁺ with Cr³⁺ at the B-site. The parent sample shows a Curie temperature (Tc) of 795 K. With 2% Cr³⁺ substitution, Tc drops to 765 K. Interestingly, further substitution (4%, 6%, 8%, and 10%) results in no significant change—Tc remains at 765 K, except for a slight drop to 762 K at 8% Cr³⁺.

What could be the underlying reason for this stabilization of Tc beyond 2% Cr³⁺ doping? Could it be due to Cr³⁺ ions’ site occupancy preferences, weakening of B–B superexchange interactions, or possible cation redistribution within the spinel structure?

Any insights or references related to magnetic exchange mechanisms and cation substitution effects in spinel ferrites would be highly appreciated.