Magnetic anomaly in CoCr2O4-δ

•CCO is shown to possess mixed states of Co (Co3+ and Co4+) and Cr (Cr2+ and 3+) ions due to the presence of oxygen vacancies.•The Co-O-Cr and Oapical-Cr-Oplanar bond angles are modified.•A novel magnetic anomaly is observed at 220 K in CCO, above the ferrimagnetic transition temperature as also confirmed from ac susceptibility measurements. The study focuses on the investigations of the impact of multiple charge states of transition metal ions on the magnetic properties of bulk CoCr2O4-δ. The electronic structure of the studied sample unveils hetero-valency in both Co and Cr cations, accompanied by the presence of oxygen vacancies in the system. The hetero-valency of Co and Cr cations, positioned respectively in tetrahedral and octahedral crystal fields, induces additional magnetic exchange interactions and alterations in the bond angles between them with respect to the stoichiometric system. These interactions lead to coexisting ferromagnetic or antiferromagnetic spin alignments of Co/Cr ions, resulting in a magnetic anomaly at 220 K, above the ferrimagnetic transition temperature 106 K (TC). The findings shed light on the interplay of charge states and distinct crystal environment of cations in determining the magnetic behavior of modified CoCr2O4.