Magnetization, magnetically modulated microwave absorption (MaMMA) and magnetoresistance in small particles of La(0.67)Ca(0.33)MnO3

We report a magnetic study of La(0.67)Ca(0.33)MnO3 fine particles obtained via sol-gel technology. An increase of the splitting between ZFC and FC has been observed as the grain size is reduced. We have estimated a critical size, D(crit), of approximately 76 nm. Smaller particles form single domains in a zero applied field. The magnetic behavior of particles with sizes less than D(crit) indicates that the blocking temperature is about 230 K, showing no MaMMA signal and an enhancement of the relative resistivity. These properties are accompanied by a magnetoresistance above 12 percent, in a field of 1 kOe, larger than the value of 5 percent observed in the ceramic samples. (Author)