Polymer encapsulation effects on the magnetism of EuS nanocrystals

Surface mediated phenomena are important in controlling the magnetism of nanocrystals. Here, we provide a versatile chemical method which allows the formation of EuS nanocrystals encapsulated in poly(styrene) (PS). These materials are the first example of a polymer based EuS nanocomposite prepared in situ. Besides their practical interest, these materials are of general relevance because they allow fundamental knowledge on the magnetism of EuS, which is commonly used as a model of an insulating ferromagnet, to be acquired. Comparatively to the starting powders of EuS nanocrystals (8 nm), in the final nanocomposites there is a decrease of the blocking temperature TB and a change in the shape of the field-cooled susceptibility curve, indicating that the intensity of dipolar interactions decreases when the nanoparticles are incorporated into PS. Differences in the magnetic properties of the EuS nanocrystals and the EuS/PS nanocomposites are also due to the appearance of a peak in the susceptibility at 60 K, in the latter sample, ascribed to surface phenomena occurring in EuS nanocrystals dispersed in the polymer matrix.