Origin of the unexpected room temperature ferromagnetism: formation of artificial defects on the surface in NaCl particles

Abstract

The unexpected room temperature ferromagnetism in pure sodium chloride (NaCl) particles with different crystal size synthesized by breaking at different times is attributed to surface defects, which provides a novel opportunity to further understand the origin of ferromagnetism in the traditional “nonmagnetic” inorganic non-metallic materials. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy suggest that breaking progress does not change the samples' body, but drastically reduces the size of the samples, what's more, it is found to enhance the strength of the ferromagnetic component with decreasing the samples' size through magnetism measure; the first-principle calculation results confirm the experimental conclusion. Ferromagnetism originates from surface effect, probably the long range ferromagnetic interactions between the surface Cl vacancies.