Abstract
We report a study on neutron diffraction and magnetic properties ol cobalt oxide CoO antiferromagnetic nanoparticles with different sizes. The nanoparticles are composed by a structurally and magnetically ordered core and a structurally ordered and magnetically disordered shell with a thickness of about 2 nm. The ordered core has cell parameters, moments direction and modulus similar to those of bulk CoO. Small differences found are attributed to an increase of the oxidation of the nanoparticles with the decrease of size. A remanent moment Mr can be induced in CoO nanoparticles by crossing the transition temperature in the presence of a magnetic field, while the magnetic structure of the antiferromagnetically ordered moments of the nanoparticles core remains unchanged after field cooling within the experimental precision, suggesting that Mr arises in the magnetically disordered shell.
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