M. Perovic

An ac susceptibility study of spin dynamics in a super spin glass nanoparticle La0.7Ca0.3MnO3 system: simultaneous relaxation processes

In this paper, we present the results of a systematic study of nonequilibrium dynamics in a strongly interacting super spin glass (SSG) nanoparticle La0.7Ca0.3MnO3 system by alternating current (ac) susceptibility measurements. Cole?Cole analysis of the obtained data revealed the simultaneous existence of two separated relaxation processes, which can be assigned to the relaxation of different magnetic entities. Along with the expected relaxation of the collective SSG phase, the existence of individual, nonagglomerated particles, which do not take part in the collective phase and relax independently, was proposed. A full dynamical scaling analysis was performed in order to elucidate the nature of the transition to a low-temperature SSG state in the interacting La0.7Ca0.3MnO3 nanoparticle sample.

The glassy behaviour of poorly crystalline Fe2O3 nanorods obtained by thermal decomposition of ferrous oxalate

Nanorod ferrous oxalate dihydrate (FeC2O4 × 2H2O) which had been synthesized by the microemulsion method, was used as a precursor in the thermal decomposition process performed in air atmosphere. The formation of nanocrystalline hematite as the final product was preceded by the appearence of an intermediate product. Comprehensive study comprising several complementary techniques (x-ray diffraction, transmission electron microscopy, selected area electron diffraction, thermogravimetric/differential thermal analyses and SQUID magnetometry) confirmed that the intermediate product corresponds to the poorly crystalline Fe2O3. Due to the specific nanorod shape and poorly crystalline structure, the investigated Fe2O3 showed high coercive field value of ~0.5 T at 5 K. Special attention in this study was devoted to the peculiar magnetic properties of poorly crystalline Fe2O3, which were thoroughly investigated by employing sophisticated experimental procedures such as relaxation of thermoremanent magnetization for different cooling fields, zero field and field cooled memory effects as well as aging experiments for different waiting times. At low temperatures and weak applied magnetic fields, the investigated system behaves similarly to spin glasses, manifesting slow, collective relaxation dynamics of magnetic moments through memory, rejuvenation and aging effects.