Temperature-dependent magnetic properties of yttrium iron garnet nanoparticles prepared by citrate sol-gel

Yttrium iron garnet (YIG) nanoparticles have been synthesized by citrate precursor gel formation with subsequent heat treatment. The single phase sample of standard garnet cubic structure was obtained after sintering the gel at 800 °C for 2 h. The lattice constant a is comparable to the value of the bulk material. The mean crystallite size determined from the broadening of X-ray diffraction (XRD) peak is 35 nm. Transmission electron microscope (TEM) analysis shows that the particles form clusters with the particle size in the range of 22-55 nm. The Curie temperature T _C of 560 K was determined via the temperature dependence of the saturation magnetization. The hysteresis loop M(H) were measured at temperatures between 5 and 560 K and in applied magnetic fields up to 20 kOe. The coercive force H _c was found to decrease monotonously with increasing temperature and above room temperature the hysteresis loops manifest the superparamagnetic character which obey Langevin theory. The blocking temperature T _B and the interparticle interaction parameter T _o were also determined and based on that an effective anisotropy constant K _eff was found to be 2.0 × 10 ⁴ erg/cm ³ for the particles of 35 nm in diameter. The thermal variation of the saturation magnetization ratio M _s(T)/M _s(5 K) is in good agreement with that reported earlier for bulk samples and thus can be very well described by the mean-field approximation for the two Fe ³⁺ sublattices.