Antiferromagnetism in colloidal nickel oxide

Magnetic susceptibility measurements have been made on a series of nickelous oxide samples prepared by the decomposition of hydrous nickel hydroxide at temperature levels of 250°--1300°C, the crystal size varying from 80--2000 A. The magnetic studies show a lowering of the antiferromagnetic transition temperatures and an enhanced non-Curie-Weiss effect as the temperature of heat-treatment and the particle size is decreased. It has been found that these effects are related to the increase in the ratio of the specific surface to the specific volume as the crystal size decreases, thereby decreasing the average number of next nearest magnetic neighbors, producing a change in the magnetic environment of the surface atoms, hence drastically altering the magnetic properties