In this study, we observe the effect of doping Nickel in Fe3O4 lattice coated with oleic acid. Fe3O4 particles agglomerate and lost their nanoparticle regime hence the addition of Nickel decreases the magnet moment slightly to get a good monodisperse particle and better stability in the nano region (10-12nm). In the present study, Ni Doped Fe3O4 MNPs were synthesized through the coprecipitation method and the single-phase has been confirmed via XRD, and coating is confirmed by FTIR. The magnetic variation is explained as Ni2+ ions (3μB) have a lesser magnetic moment than Fe2+ (4μB) and Fe3+ (5μB) ions. As a result, M = MB-MA gives the net magnetization. The saturation magnetization of the bulk magnetite (Fe3O4) is found to be lower i.e. (0.5 emu/g for x=0.7) as compared to the Ms value for the synthesized Fe3O4 nanoparticles (3 emu/g). Due to the presence of vacancy at the octahedral site of Fe/Ni, the magnetization value of x=0.1 decreases abnormally (fig.1). The suppression of saturation magnetization (Ms) as the concentration of Ni2+ ions rises might be because of the reduced magnetic field contribution by Ni2+ ions compared to Fe2+ and Fe3+ ions as shown in insert fig.1. To investigate the spin dynamics in NixFe3-xO4 electron paramagnetic resonance (EPR) measurements have been performed as shown in the power adsorption derivatives (PAD) (fig 2). The resonance field (Hres) also lies in the range from 3.25 kOe to 3.75 kOe while increasing the Ni concentration of NixFe3-xO4 (0 ≤ x ≤ 0.7) nanoparticles in corroboration with field-dependent magnetic behavior where Ni suppresses the moment and resulted in the random orientation of the spins. The decrease in peak-to-peak line width (ΔHPP) is attributed to the weak magnetic interactions (super-exchange) between Ni-O-Fe with the increase in doping Ni concentration from x = 0.1 to x = 0.7. The detailed structural and electron paramagnetic resonance measurements on oleic acid-coated NixFe3-xO4 (0 ≤ x ≤ 0.7) provide a tunable spin dynamic and improve the saturation magnetization, which is a key parameter for spintronics, magneto-optoelectronics, EMI shielding, and supercapacitor applications.
References:
1. K. Usadel Phys. Rev. B. 73 (2006).
2. E. De Biasi, E. Lima, C.A. Ramos, A. Butera, R.D. Zysler, J. Magn. Magn. Mater. 326 (2013) 138–146.
3. A. Sukhov, K.D. Usadel, U. Nowak, J. Magn. Magn. Mater. 320 (2008) 31–35.
4. C.A. Ramos, E. De Biasi, R.D. Zysler, E. Vassallo Brigneti, M. Vázquez, J. Magn. Magn. Mater. 316 (2007) e63–e66.

Figure 1

Figure 2