Canted antiferromagnetism on a nanodimensional spherical surface geometry was investigated on manganese carbonate MnCO${}_3$ small hollow nanospheres of mean diameter 7.0 ± 0.3 nm and shell thickness of 0.7 nm, by performing magnetic measurements and specific heat study, in comparison to the bulk form of the same material. Contrary to the expectation that small magnetic nanoparticles become superparamagnetic, the phase transition to the canted antiferromagnetic (AFM) state in the MnCO${}_3$ hollow nanospheres is preserved and retains, at a qualitative level, all the features of the canted AFM state of the bulk material. At a quantitative level, some significant differences between the hollow nanospheres and the bulk were observed, which can all be explained by the weakened interspin interactions in the hollow nanospheres due to reduced atomic coordination by the neighboring atoms. This makes the canted AFM structure of the hollow nanospheres more soft and fragile with respect to external forces like the magnetic field, as compared to the rigid and robust structure of the bulk material.

• Received 8 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.224407