Magnetism of natural composite of halloysite clay nanotubes Al2Si2O5(OH)4 and amorphous hematite Fe2O3

The natural composite of tubular mineral halloysite Al2Si2O5(OH)4 and nanoparticles of poorly crystallized or amorphous hematite Fe2O3 were investigated by means of transmission electron microscopy, electron spin resonance, Mössbauer spectroscopy and quantitatively characterized in measurements of low temperaturemagnetic susceptibility χ. The diamagnetic response χdiaof the halloysite nanotubes is superimposed on complex paramagnetic behavior χpara due to the presence of iron impurities in various aggregate forms. The low temperature upturn in χ(T) dependence is ascribable to isolated Fe3 + ions substituting Al3 + ions, the step-like anomaly at Tg ~ 80 K is the signature of glassy magnetic order in nanosized inclusions of amorphous hematite.