Influences of morphology, cation distribution and surface spin canting on magnetic and hyperfine properties of mechanically activated and subsequently heat treated nanosized Co0.8Zn0.2Fe2O4 exhibiting excellent catalytic activity

Abstract

Herein, we have shown that the particle size, cation redistribution, interparticle interactions, surface spin disorder and strain induced anisotropy play a pivotal role in shaping the magnetic and hyperfine properties of nanosized Co0.8Zn0.2Fe2O4 samples prepared by coprecipitation method followed by high energy ball milling and subsequent thermal treatment. Three samples with different particle size viz., 23 nm (CZ1), 34 nm (CZ2) and 42 nm (CZ3) are characterized by powder x-ray diffraction, transmission electron microscopy and energy dispersive x-ray spectroscopy studies. The samples are well-crystalline, single-phase spinel with appropriate stoichiometry, assorted size and shape. All three samples are magnetically ordered at 300 K with MSAT and HC values 75.22, 81.07, 82.89 emu g−1, respectively, and 530, 460, 420 Oe, respectively. The values of coercivity at 10 K are remarkably high. Cation distribution of CZ1, CZ2 and CZ3 as estimated by taking into account the results of infield Mössbauer spectroscopic study and powder x-ray diffraction in conjugation are: (Co0.272+Zn0.202+Fe0.533+)A[Co0.532+Fe1.473+]BO4 (core region of CZ1), (Co0.432+Zn0.202+Fe0.373+)A,[Co0.372+Fe1.633+]BO4 (shell region of CZ1), (Co0.282+Zn0.202+Fe0.523+)A[Co0.522+Fe1.483+]BO4 and (Co0.242+Zn0.202+Fe0.563+)A[Co0.562+Fe1.443+]BO4, respectively. Further, this result has been validated theoretically. Owing to the core-shell structure (ferrimagnetically ordered core surrounded by a disordered shell), sample CZ1 having particle size below calculated critical diameter (∼ 27 nm) exhibits exchange bias effect. All three samples display excellent catalytic activity in the multicomponent reaction for the synthesis of coumarin-3-carboxamide. CZ1 shows best catalytic activity owing to its high surface to volume ratio.