Muon Irradiation of ZnO Rods: Superparamagnetic Nature Induced by Defects

Abstract

In this work, through a combination of photoluminescence spectroscopy, X-ray powder diffraction and magnetic measurements, it is determined that ZnO rods, made hydrothermally using a combination of magnetic field with respect to the force of gravity, exhibit superparamagnetic properties which emerge from Zn defects. These Zn defects result in a size-dependent superparamagnetic property of the rods. Red emissions, characteristic of Zn vacancies, and magnetic susceptibility both increased with decreasing rod size. The ZnO rods have significantly larger superparamagnetic cluster sizes (one order of magnitude) and lower fluctuation rates when compared to other superparamagnetic particles.

The Interplay of Growth Mechanism and Properties of ZnO Nanostructures for Different Applications

“…The ZnO nanoflowers grown in water showed the highest photocatalytic activity due to the large surface area and increase in the structural defects. These defects, oxygen vacancies, and zinc interstitials, [ 32 ] can serve as centers to trap electrons, thereby inhibiting recombination of electrons and holes. Furthermore, preferential crystal growth is regulated by the surface energy of each plane.…”

“…effects but in biosensors. [32,51,64] In addition, gas sensing abilities are reliant on the size of morphology of the nanostructures as decreased width of the nanorods heightens the surface depletion effect which increases sensitivity. [65] Other studies have shown the greater surface area and surface defects of ZnO nanoflowers enhance the response as there is increased adsorption of the target gas molecule.…”

“…[127] The shift in peaks shown from the UV-vis can be a result of the quantum confinement which is caused from the change in mean particle size. Decreasing the size of the nanostructures increases the band gap; thus, the optical differences between the bulk and nano [32] Copyright 2022, MDPI. materials show great potential for photocatalysis and optical sensing.…”

“…In a study done by Landry et al., they prepared ZnO nanorods on ITO substrates by hydrothermal synthesis, and the effects of an external magnetic field were studied. [ 32 ] The presence of the external magnetic field allowed for control over the morphology and resulting magnetic properties. In most cases, a Gauss meter could be used to determine the exact magnitude and direction of relatively small (smaller than 1 Tesla) applied magnetic fields.…”

“…Therefore, it was determined that the synthesized nanorods were exhibiting super‐paramagnetic properties. [ 32 ] This is important for various potential medical applications as the magnetic nature of the nanorods can be beneficial for drug delivery or magnetic‐field induced hyperthermia in cancer treatments. [ 33 ] Therefore, further understanding of the effect of each reaction parameter on the size and properties of the ZnO nanorods is significant for potential applications.…”