Anomalous ferromagnetic response in Na₂Ti₃O₇ nanopowder obtained by the sonochemical method

In this work we analyzed the preparation of high-quality Na₂Ti₃O₇ nanopowders by using the sonochemical method. X-ray diffraction and transmission electron microscopy analyses revealed that a predominant amorphous phase, combined with small nanocrystals are presented in the as-prepared sonicated powders. The purity of the samples has been determined by energy dispersive x-ray analysis, revealing that only Na, Ti, and O are existing in the samples. On the other hand, an unusual Na₂Ti₃O₇ magnetic response is found, typical of a soft ferromagnetic material. The weak ferromagnetic behavior observed in the hysteresis curves, with coercive field of 65 Oe and magnetic saturation of 8.58 × 10^-6 emu g^-1 observed in the Arrott plot, indicated a ferromagnetic second order transition.