Suppression of low temperature magnetic ordering in samarium nanoparticles

The role of finite size effects on magnetic order has been investigated in samarium nanoparticles prepared by physical vapor deposition. A dense layer composed of distinct nanoparticles with a mean particle diameter of 26 nm was deposited on a diamagnetic substrate. M(T) measurements identify the expected pair of antiferromagnetic ordering temperatures in the bulk Sm precursor, at 113 K and 14 K, where the magnetic unit cell for the lower ordering temperature is 10.36 nm along the c-axis. The high temperature ordering of the hexagonal sites in the Sm nanocrystals is slightly decreased with respect to that of bulk Sm, while the low temperature transition associated with the cubic sites is significantly suppressed. The observed changes are attributed to finite size effects, with ordering suppressed as the particle radius approaches the length of the magnetic unit cell, and surface moments become more prominent.