Abstract
Monatomic (Fe, Co) and bimetallic (FePt and CoPt) nanoparticles were prepared by exploiting the self-organization of precursor loaded reverse micelles. Achievements and limitations of the preparation approach are critically discussed. We show that self-assembled metallic nanoparticles can be prepared with diameters d = 2–12 nm and interparticle distances D = 20–140 nm on various substrates. Structural, electronic and magnetic properties of the particle arrays were characterized by several techniques to give a comprehensive view of the high quality of the method. For Co nanoparticles, it is demonstrated that magnetostatic interactions can be neglected for distances which are at least 6 times larger than the particle diameter. Focus is placed on FePt alloy nanoparticles which show a huge magnetic anisotropy in the L10 phase, however, this is still less by a factor of 3–4 when compared to the anisotropy of the bulk counterpart. A similar observation was also found for CoPt nanoparticles (NPs). These results are related to imperfect crystal structures as revealed by HRTEM as well as to compositional distributions of the prepared particles. Interestingly, the results demonstrate that the averaged effective magnetic anisotropy of FePt nanoparticles does not strongly depend on size. Consequently, magnetization stability should scale linearly with the volume of the NPs and give rise to a critical value for stability at ambient temperature. Indeed, for diameters above 6 nm such stability is observed for the current FePt and CoPt NPs. Finally, the long-term conservation of nanoparticles by Au photoseeding is presented.
Highlights
Magnetic nanoparticles have been the focus of research for over 60 years [1,2]
In this article we address the preparation of magnetic NPs by precursor loaded reverse micelles on different supports
We show that magnetostatic interactions can be neglected for micellebased NPs, which is used in a step where the effective anisotropy Keff of FePt and CoPt is determined by simple Stoner–Wohlfarth approach using a bimodal distribution of Keff
Summary
Magnetic nanoparticles have been the focus of research for over 60 years [1,2]. These investigations were prompted by both, fundamental aspects of the magnetism of small particles and clusters [3,4], and an increasing interest by industry, especially in the field of data storage (first magnetic tapes and later hard disk drives) [5,6]. Unlike all other preparation methods, the micelle approach leads to supported NPs with significantly larger interparticle distances (D > 20 nm) which is especially appealing for two reasons: (i) the magnetostatic interaction of NPs is very small and individual magnetic properties can by extracted, and (ii) the larger distance between NPs allows their annealing as opposed to colloidal NPs where extended heat treatment leads to agglomeration [43] This aspect is especially useful for systems which undergo a phase transition and thereby improves their magnetic properties such as in the cases of FePt or CoPt NPs which are of technological interest due to their high magnetocrystalline anisotropy in the L10 phase. The presently introduced micellar route, which offers control of both particle size and interparticle distance, fulfills this requirement to a considerable extent
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
