Chain length dependence of polyol synthesis of zinc ferrite nanoparticles: why is diethylene glycol so different?Electronic supplementary information (ESI) available: Experimental details for spectroscopic determination of glycoldehyde and Fig. S1-S3. See DOI: 10.1039/c2dt32026f

Superparamagnetic ZnFe 2 O 4 nanoparticles with size range of 28-38 nm were synthesized by polyol process based on use of varying chain length glycols as solvent. We have offered, for the first time, the plausible mechanism behind in situ formation of zinc ferric oxalate hydroxide hydrate [Fe 2 Zn(C 2 O 4 ) 2 (OH) 3 ] + ·4H 2 O complex from diethylene and polyethylene glycol. We are also reporting, the magnetic properties of above complexes. We have found a ferromagnetic ordering in precursor complex compounds. The intermediate hydrocarbon chain between the oxalato bridged metal cations plays a crucial role in obtaining anomalous magnetic behavior. ZnFe 2 O 4 nanoparticles obtained after annealing the DEGylated precursor complex (precursor complex formed in diethylene glycol) showed the highest superparamagnetic (SPM) behavior (22.4 emu g −1 ) among others. The reasons for anomalous SPM behavior of ZnFe 2 O 4 nanoparticles are explained on the basis of the degree of inversion of the spinel structure, high surface-to-volume ratio, which causes non-collinear spin arrangement in a surface layer and higher oxygen concentration on the surface of dead organic layer, which increases the unpaired valence electrons leading to uncompensated surface spins. Zinc ferric oxalate hydroxide hydrate complex synthesized by DEG shows weak ferromagnetism which on annealing forms ZnFe 2 O 4 showing superparamagnetic behavior.