Superparamagnetic Properties of Ni_0.7Zn_0.3Fe₂O₄Nanoparticles

Nanoparticles $Ni_0.7Zn_0.3Fe_2O_4$ is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, $M\ddot{o}ssbauer$ spectroscopy, and VSM. $Ni_0.7Zn_0.3Fe_2O_4$ powders annealed at $300^\circC$ have a spinel structure and behaved superparamagnetically. The estimated size of $Ni_0.7Zn_0.3Fe_2O_4$ nanoparticle is about 11 nm. $Ni_0.7Zn_0.3Fe_2O_4$ annealed at 400 and $500^\circC$ has 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). Blocking temperature $(T_B)\;of\;Ni_0.7Zn_0.3Fe_2O_4$ nanoparticle is about 260 K. The magnetic anisotropy constant of $Ni_0.7Zn_0.3Fe_2O_4$ annealed $300^\circC$ were calculated to be $1.7X10^6\;ergs/cm^3$. Also, temperature of the sample increased up to $43^\circC$ within 7 minutes under AC magnetic field of 7 MHz.