Size effects on the Neel temperature of antiferromagnetic NiO nanoparticles.

Size effects on the Neel temperature of antiferromagnetic NiO nanoparticles.

Among all antiferromagnetic transition metal monoxides, NiO presents the highest Neel temperature (T-N similar to 525 K). In this work, the size-dependent reduction of T-N in NiO nanoparticles with average diameters (D) ranging from 4 to 9 nm is investigated by neutron diffraction. The scaling law followed by T-N(D) is in agreement with the Binder theory of critical phenomena in low-dimensional systems. X-ray absorption fine structure measurements link the decrease of T-N to the occurrence of size effects (average undercoordination, bond relaxation and static disorder) in the nearest and next-nearest Ni coordination shells that hold the key for the maintenance of the antiferromagnetic order. (C) 2016 Author(s).