Magnetic nanoparticles (MNPs) are widely used in biomedical applications. Biocompatibility and superparamagnetic response of the MNPs make them viable, especially as contrast agents in magnetic resonance imaging (MRI) and tracer agents in magnetic particle imaging (MPI). Nickel ferrites (NiFe2O4) coated with citric acid (CA) and polyacrylic acid (PAA) were synthesized by hydrothermal process. Nickel ferrites were structurally characterized by fourier transformed infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS), and thermogravimetric analysis (TGA). Nickel ferrites were also magnetically evaluated with electron-spin resonance (ESR), and physical properties measurement system (PPMS). The samples crystallite size of 9-12 nm achieved with XRD is in good agreement with the magnetic domain size that was obtained by PPMS results. Furthermore, nickel ferrites were also evaluated with magnetic particle spectroscopy (MPS) to determine the expected performance in MPI scanner. MPS results of NiFe2O4@PAA showed minimum relaxation time and high resolution (FWHM, mT) as compared to Vivotrax (magnetic insight) and Perimag (micromod) commercial reference tracers used in MPI. All results show that nickel ferrites have a great potential to become an optimum tracer agent for MPI.