Remanent magnetization in CoO antiferromagnetic nanoparticles

We report a study on the remanent magnetization Mr induced by field cooling across the ordering temperature TN in antiferromagnetic CoO 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. Mr is shown to be proportional to the cooling field Hcool. The low-temperature saturation values of Mr Mr 0 in the CoO nanoparticles are about two orders of magnitude higher than those found for bulk CoO. Mr /Mr 0 of CoO nanoparticles scales with temperature in a single curve, independently on the magnitude of Hcool and on nanoparticles size, except for temperatures near to TN since TN is size dependent.