Magnetic properties of self-assembled nanoscale La_2/3Ca_1/3MnO₃ particles in an alumina matrix

We have investigated the processing and properties of La_2/3Ca_1/3MnO₃ self-assembled nanodots formed in a nonmagnetic alumina matrix, which were produced by a pulsed-laser deposition process. The size of the nanodots was found to be in the range of 10-15 nm using high-resolution transmission electron microcopy. The average interlayer separation between two dots has been found to be 2-5 nm, which is sufficient to decouple the magnetic grains. The decoupling of the grains is supported by the zero-field-cooled and field-cooled magnetization (M) data. The coercivity of the La_2/3Ca_1/3MnO₃ nanodots has been measured using magnetization measurements as a function of field (H) at different temperatures above and below the blocking temperature of the samples. The coercivity is found to vary from 600 Oe at 10 K to 400 and 200 Oe at 20 and 50 K, respectively. Above the blocking temperature, the sample is found to transform to a superparamagnetic magnetic state, resulting in the disappearance of any hysteresis in the M-H loops.