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Nanoparticles Ni0.9Zn0.1Fe2O4 is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, Mssbauer spectroscopy, and VSM. Ni0.9Zn0.1Fe2O4 powders annealed at 300oC have a spinel structure and behaved superparamagnetically. The estimated size of Ni0.9Zn0.1Fe2O4 nanoparticle is about 10 nm. The hyperfine fields at 13 K for the A and B patterns are found to be 533 and 507 kOe, respectively. The ZFC curves are rounded at the blocking temperature (TB) and show a paramagnetic-like behavior above TB. TB of Ni0.9Zn0.1Fe2O4 nanoparticle is about 250 K. Nanoparticles Ni0.9Zn0.1Fe2O4 annealed at 400 and 500oC have a typical spinel structure and is ferrimagnetic in nature. The isomer shifts indicate that the iron ions were ferric at the tetrahedral (A) and the octahedral (B). The saturation magnetization of nanoparticles Ni0.9Zn0.1Fe2O4annealed at 400 and 500oC are 40 and 43 emu/g, respectively. The magnetic anisotropy constant of Ni0.9Zn0.1Fe2O4 annealed at 300oC were calculated to be 1.6??106 ergs/cm3.