Magnetic properties of La0.7Sr0.3MnO3 nanopowders

The peculiarities of the magnetization of a nanopowder (particle size 12 nm) of the manganite La0.7Sr0.3MnO3 are investigated. It is shown that for temperatures below the Curie point the magnetization of the powder is of the ferromagnetic type with a relatively small value of the remanent magnetization. The minimum of the derivative of the spontaneous magnetization with respect to temperature lies 20 K below the Curie temperature determined by extrapolation of the temperature dependence of the coercivity. These features of the magnetization are a consequence of a large variance of the anisotropy fields of the particles, the distribution function for which was determined from incremental hysteresis loops. It is also found that the Curie temperature of the powder has a strong variance, with an rms deviation of at least 20 K. The mean value of the Curie temperature of the particles is 325 K. The spontaneous magnetization of the powder particles does not have (even in the low-temperature region) a saturation region. This temperature dependence of the spontaneous magnetization influences the trend of the temperature dependence of the coercive field, leading to a deviation from the Neel-Brown law. It is also shown that for the given ensemble of particles the blocking temperature corresponds to the temperature of the maximum of the ratio of the magnetization measured after cooling in the zero-field regime to the spontaneous magnetization.