Superparamagnetism is a phenomenon caused by quantum effects in magnetic nanomaterials. Zero-valent metals with diameters below 5 nm have been suggested as superior alternatives to superparamagnetic metal oxides, having greater superspin magnitudes and lower levels of magnetic disorder. However, synthesis of such nanometals has been hindered by their chemical instability. Here we present a method for preparing air-stable superparamagnetic iron nanoparticles trapped between thermally reduced graphene oxide nanosheets and exhibiting ring-like or core-shell morphologies depending on iron concentration. Importantly, these hybrids show superparamagnetism at room temperature and retain it even at 5 K. The corrected saturation magnetization of 185 Am(2) kg(-1) is among the highest values reported for iron-based superparamagnets. The synthetic concept is generalized exploiting functional groups of graphene oxide to stabilize and entrap cobalt, nickel and gold nanoparticles, potentially opening doors for targeted delivery, magnetic separation and imaging applications.

Department of Experimental Physics and Department of Physical Chemistry Regional Centre of Advanced Technologies and Materials Faculty of Science Palacky University in Olomouc Slechtitelu 27 783 71 Olomouc Czech Republic

Department of Inorganic Chemistry University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Czech Republic

Division of Chemistry and Biological Chemistry School of Physical and Mathematical Sciences Nanyang Technological University 637371 Singapore Singapore

Institute of Scientific Instruments The Czech Academy of Sciences Kralovopolska 147 612 64 Brno Czech Republic

Nat Commun. 2019 Jun 18;10(1):2696. doi: 10.1038/s41467-019-10702-2. PubMed

Nat Commun. 2020 Nov 25;11(1):6116. doi: 10.1038/s41467-020-19968-3. PubMed

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