Temperature-dependent XRD, IR, magnetic, SEM and TEM studies of Jahn–Teller distorted NiCr2O4 powders

•NiCr2O4 starts to crystallize near 750 °C.•Coexistence of cubic and tetragonal phases of NiCr2O4 was revealed.•Temperature of the Jahn–Teller distortion is lowered due to the size effects.•Evidences of tetragonal and orthorhombic distortions were found.•Weak spin–phonon interactions were evidenced.

In the present work we report detailed structural, magnetic and phonon properties of NiCr2O4 powders synthesized via a simple coprecipitation method. Temperature-dependent XRD as well as temperature-dependent IR studies reveal that cubic to tetragonal phase transition is lowered due to size effects. Observed changes in the IR spectra indicate that the paramagnetic–ferrimagnetic phase transition taking place at 74 K is related to further lowering of symmetry to orthorhombic system. Assignment of modes was proposed and factor group analyses in three possible symmetries were carried out. Our results show strong anomalies due to the Jahn–Teller tetragonal distortion and weak due to the orthorhombic distortion and onset of collinear ferrimagnetic order. Shifts of wavenumbers observed below 31 K, where the onset of antiferromagnetic ordering occurs, were attributed to spin–phonon interactions.

Graphical abstractXRD pattern of NiCr2O4 sample synthesized via a coprecipitation method followed by calcination at 1000 oC.Figure optionsDownload full-size imageDownload as PowerPoint slide