Supplement Number 1

The supplementary material contains the following: 1) Structural characterization of zinc-substituted cobalt ferrite nanoparticles: Figure S1: (a) XRD patterns, (b) TEM micrographs, and (c) particle size distribution; Table S1: Chemical composition, average crystallite size, lattice parameter, average particle size, and weight loss. 2) Additional magnetic measurements and calculations: Equation S1: Critical diameter calculation for a ferromagnetic sphere; Table S2: Experimental values of calculated critical diameter; Figure S2: (a) MDCD as a function of HR and (b) switching field distribution at 5 K; Figure S3: Rate of temperature reduction of magnetization (R); Figure S4: ZFC and FC magnetization curves; Table S3: Peak (Tmax), irreversibility (Tirr) and blocking (TB) temperatures estimated from ZFC-FC curves.