Pushing up the magnetisation values for iron oxide nanoparticles via zinc doping: X-ray studies on the particle's sub-nano structure of different synthesis routes

Abstract

The maximum magnetisation (saturation magnetisation) obtainable for iron oxide nanoparticles can be increased by doping the nanocrystals with non-magnetic elements such as zinc. Herein, we closely study how only slightly different synthesis approaches towards such doped nanoparticles strongly influence the resulting sub-nano/atomic structure. We compare two co-precipitation approaches, where we only vary the base (NaOH versus NH), and a thermal decomposition route. These methods are the most commonly applied ones for synthesising doped iron oxide nanoparticles. The measurable magnetisation change upon zinc doping is about the same for all systems. However, the sub-nano structure, which we studied with Mössbauer and X-ray absorption near edge spectroscopy, differs tremendously. We found evidence that a much more complex picture has to be drawn regarding what happens upon Zn doping compared to what textbooks tell us about the mechanism. Our work demonstrates that it is crucial to study the obtained structures very precisely when "playing" with the atomic order in iron oxide nanocrystals.

Iron Oxide Nanoparticles as Imaging and Therapeutic Agents for Atherosclerosis

“…However, it is known that doping with nonmagnetic elements can improve the maximum magnetization of the nanoparticle to improve MRI capability. 45 Several papers in the literature have reported successful synthesis with dopants such as lanthanides, 46,47 transition metals, 48 and gadolinium contrast agents 39 for several applications ranging from radiotherapy, microscopy, and in vivo targeted imaging.…”

Tuning the Magnetic Moment of Small Late 3d-Transition-Metal Oxide Clusters by Selectively Mixing the Transition-Metal Constituents

“…Unfortunately, this is precisely the weak point of TMO-NP in general, since TM–O interactions induce antiparallel (AP) magnetic couplings which render them to be in a low-spin state, and consequently to have a small total magnetic moment. To overcome this issue, attempts have been made to increase the total moment of TMO-NP by their doping with another element [ 23 , 24 ]. In this context, Szczerba et al have experimentally investigated the doping of iron oxide nanoparticles with Zn with the goal of avoiding the spin missalignment, thereby enhancing the total moment [ 24 ].…”

“…To overcome this issue, attempts have been made to increase the total moment of TMO-NP by their doping with another element [ 23 , 24 ]. In this context, Szczerba et al have experimentally investigated the doping of iron oxide nanoparticles with Zn with the goal of avoiding the spin missalignment, thereby enhancing the total moment [ 24 ]. The idea behind it is that Zn substitutes Fe atoms at tetrahedral sites, which are were the Fe atoms antiparallelly couple with the rest in the original iron oxide NP.…”

Selective magnetometry of superparamagnetic iron oxide nanoparticles in liquids

“…57 Fe Mössbauer spectroscopy (MS), magnetic particle spectroscopy (MPS) and X-ray magnetic circular dichroism (XMCD) are often used for characterization of iron oxide nanoparticles. 9,16,23,[35][36][37][38][39][40][41] Although the XMCD spectra has a lower energy resolution and the experimental setup is more involved than that of MS and MPS, XMCD has the advantage that it can be applied to any magnetic element. Moreover, the XMCD spectral shape is not prone to relaxation effects.…”

“…To facilitate the analysis these are transformed to magnetic volumes assuming particles have a spherical shape and volume magnetization of 350 kA m −1 . 37 Resulting distribution is presented in Fig. 3(b) as a function of particle radius, It is compared to the volume magnetization measurements performed using vibrating sample magnetometry (VSM) on the same suspension (black squares).…”