Peer-Reviewed Journal Details
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Barry, L; Holmes, JD; Otway, DJ; Copley, MP; Kazakova, O; Morris, MA;
Journal of Physics-Condensed Matter
Unusual magnetism in templated NiS nanoparticles
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Nanostructured NiS was prepared by inclusion into anodic alumina templates. The resultant particles were found to be stoichiometric and highly crystalline. The particles displayed small particle superparamagnetism, and a low temperature (at 48 K (T-sg)) spin-freezing phenomenon (a spin-glass) and higher temperature (170 K) thermal blocking of small particle magnetic moment fluctuations were both observed for the first time for a sulfide material. Very unusually, these NiS materials are quite distinct from antiferromagnetic nanoparticulate sulfide materials, as they display a high temperature ferromagnetic-like phase. The saturation magnetization, the remanent magnetization, the coercivity and the ferromagnetic mass susceptibility were measured as 0.58 emu g(-1) (at 100 K), 0.19 emu g(-1), 219.5 Oe (at 170 K) and similar to 900 x 10(-6) emu Oe(-1) g(-1) respectively and these are consistent with a moderately strong ferromagnetism. The materials had an unexpectedly high Curie temperature of 390 K. The decrease of the saturation magnetization value at 30 K suggests that the ferromagnetic response is a surface phenomenon and the high coercivity of the paramagnetic component well above T-sg suggests that the core can be described as superparamagnetic.

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