Diamagnetic turn into superparamagnetic
There have been some reports of bulk diamagnetic subtance develop magnetism on size reduction. For example claim about Ag nanoparticles and possible Pd and Au nanoparticles as well. But these claims are still controversial. Some ab initio calculations all shows small magnetism in Ag clusters. We already had some discussions about this previously Research Gate. Kai Fauth expressed a lot of ideas regarding this in his discussions. But some claims are not beyond doubts about the samples being contaminated by magnetic impurities.
I also suspects this possibility although some reports claim. If the sample contains traces of impurities, then it can show paramagnetic or even ferromagnetic. In my view, there is no better theoretical idea on this matter.
It is well known that superparamagnetism is caused with the magnetism in small ferromagnetic or ferrimagnetic nanoparticles. In this case the quasi-paramagnetic behavior of materials appears. Direction of magnetization randomly flip under the thermal excitation. An external magnetic field is able to magnetize the nanoparticles similarly to a paramagnet. Thus, in my opinion, the bulk diamagnetic can not be superparamagnetic as a result of decrease of its size.
I have already asked a question on Researchgate.
"Y. Björnstahl in 1921 observed a significant magnetically induced birefringence and dichroism in gold and silver colloids [ Björnstahl Y., Phil. Mag. 6 (1921)352]. Gold being diamagnetic and the colloidal particles were considered to be isotropic it was difficult to interpret the results [P. C. Scholten, Indian J. Engineering and Material Science, 11(2004)323]. Hori et al have experimentally shown that nano size gold particles exhibit ferromagnetic magnetization which increases with size and attains a maximum at 3 nm and then decreases [ Phys. Rev. B 69, 174411, (2004)]. A theoretical interpretation of the above work is given by Michel et al. [Phys. Rev. B 76, 224409 (2007)]. "
I do not think any one has tried to repeat experiments of Björnstahl. Longback I tried but failed!!
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