Size effects on the Néel 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).