Magnetic Behavior of Zn-Doped Fe3O4 Nanoparticles Estimated in Terms of Crystal Domain Size

A series of zinc (Zn) doped Fe 3 O 4 nanoparticles with different Zn concentrations represented as Zn x Fe 3– x O 4 (0 < x ≤ 1) were synthesized by the chemical coprecipitated technique mainly in the presence of sodium dodecyl benzene sulfonate (SDBS) as one of the surface modifiers. The prepared zinc-doped Fe 3 O 4 nanoparticles were characterized by a vibrating sample magnetometer (VSM), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM). The VSM measurements showed that magnetization vs applied magnetic field for zinc-doped particles showed an increasing curve with very small hysteresis and that the saturation magnetization ( M s ) of Zn x Fe 3– x O 4 reached a maximum 80.93 emu/g at x = 0.2. The experimental result exhibited that Zn 0.2 Fe 2.8 O 4 nanoparticles coated with different surface modifiers give good dispersivity and outstanding stability in the organic dispersed phase compared with noncoated particles. The value of M s decreased with further increase in x beyond 0.2. Such decreasing behavior of the magnetization was elucidated on the basis of two factors. One was the comparison between experimental and calculated curves of the average magnetic moment of paramagnetism associated with superexchange interactions among magnetic ions in tetrahedral space (A-site) and octahedral space (B-site) in a crystal unit with face-centered cubic inverse-spinel structure. The second was x -dependence on the WAXD curve profile calculated based on the modified Laue function for a diffraction peak from the (311) plane. The observed and calculated WAXD intensity curves revealed that the a -axis became longer and the corresponding crystal size became smaller with increasing x up to 0.4. In contrast, further increase beyond 0.4 provided the inverse relationships. The a -axis became shorter, and the crystal size became bigger. They were close to those of Fe 3 O 4 at x = 1, indicating that x = 0.4 is the zinc doping limit to form a zinc-doped Fe 3 O 4 crystal structure.