Unusual crystallite growth and modification of ferromagnetism due to aging in pure and doped ZnO nanoparticles

Abstract

We report the unusual growth of pure and Fe doped ZnO nanoparticles prepared by forced hydrolysis, and the weakening of ferromagnetism due to aging in ambient conditions. More than four dozen nanoparticle samples in the size range of 4 -20 nm were studied over 1 to 4 years. The as-prepared samples had significant changes in their crystallite sizes and magnetization as they aged in ambient conditions. Detailed studies using x-ray diffraction and transmission electron microscopy (TEM) demonstrated that the crystallite size increased by as much as 1.4 times. Lattice parameters and strain also showed interesting changes. Magnetometry studies of Zn 1-x Fe x O with x = 0-0.2 showed ferromagnetism at room temperature; however, keeping the samples in ambient conditions for one year resulted in modifications in the crystallite size and magnetization. For the Zn 0.95 Fe 0.05 O sample, the size changed from 7.9 nm to 9.0 nm, while the magnetization decreased from 1 memu/g to 0.2 memu/g . Both magnetic and structural changes due to aging varied with the environment in which they were stored, indicating that these changes are related to the aging conditions.

Review of nanomaterial aging and transformations through the life cycle of nano-enhanced products

“…Meanwhile, changes in the crystal structure and/or the particle surface may occur and defects affecting product robustness may be observed over time (Kenning et al, 2011). Change in particle size is a common trend, such as an example reported by Thurber et al (2012), unprotected ZnO powders almost doubled in diameter after four years of exposure to ambient air. In another example of particle growth, formation of ZnO nanocrystals in powder form at room temperature was dependent on relative humidity and partial pressure (Ali and Winterer, 2009).…”

Effects of Precursor Concentration in Solvent and Nanomaterials Room Temperature Aging on the Growth Morphology and Surface Characteristics of Ni–NiO Nanocatalysts Produced by Dendrites Combustion during SCS

“…Size changes are often observed as reported by Thurber et al [32] where unprotected zinc oxide powders doubled in diameter after four years of exposure to the environment. Formation of the same nanocrystals was dependent on humidity and pressure [33].…”

d° Ferromagnetism of Magnesium Oxide

“…In case of HfO 2 , high-spin defect states in isolated cation vacancy sites couple ferromagnetically with short-range magnetic interaction to establish a ferromagnetic ground state [26]. Thus d • ferromagnetism can not only be interpreted in terms of vacancies/defects, but understanding of appropriate mechanism revealing the interaction that leads to existence of such an effect upto understanding of appropriate mechanism revealing the interaction that leads to existence of such an effect upto long-range order is another aspect [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Hence, investigation of the nature of magnetic interaction, along with the nature of defects in these materials, are important to understand the concept of d° ferromagnetism.…”

“…Moreover, oxygen vacancies associated with misfit stress at the film substrate interface in SnO 2 , CeO 2 , Al 2 O 3 , ZnO, MgO, and HfO 2 thin films are responsible for RTFM [16]. Vacancy mediated magnetism occurs in CuO [17] and ZnO [18,19]; oxygen vacancy induced magnetism in zinc peroxide [20] and CeO 2 [21]; and surface vacancy induced magnetism in NiO [22]. Thus, these studies reveal that defects in the form of vacancies are the source of this behavior [11][12][13][14][15][16][17][18][19][20][21][22], however, sustainability of this magnetism up to long-range order requires exigency of the mechanism of interaction among these sources.…”

“…To date, this magnetism is observed in a variety of materials with different sources of origin and is classified accordingly [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”