Abstract
Nanoparticle generation by aerosol methods, particularly spark ablation, has high potential for creating new material combinations with tailored magnetic properties. By combining elements into complex alloyed nanoparticles and controlling their size and structure, different magnetic properties can be obtained. In combination with controlled deposition, to ensure nanoparticle separation, it is possible to minimize interparticle interactions and measure the intrinsic magnetic property of the nanoparticles. Most magnetic materials are highly sensitive to oxygen, and it is therefore crucial to both understand and control the oxidation of magnetic nanoparticles. In this study, we have successfully generated oxidized, bimetallic FeCr and FeMn nanoparticles by spark ablation in combination with a compaction step and thoroughly characterized individual particles with aerosol instruments, transmission electron microscopy and synchrotron-based X-ray photoelectron spectroscopy. The generated nanoparticles had an almost identical transition-metal ratio to the electrodes used as seed materials. Further, we demonstrate how the carrier gas can be used to dictate the oxidation and how to alternate between self-passivated and entirely oxidized nanoparticles. We also discuss the complexity of compacting alloyed nanoparticles consisting of elements with different vapor pressures and how this will affect the composition. This knowledge will further the understanding of design and generation of complex alloyed nanoparticles based on transition metals using aerosol methods, especially for the size regime where a compaction step is needed. As a proof of concept, measurements using a magnetometer equipped with a superconducting quantum interference device were performed on samples with different particle coverages. These measurements show that the magnetic properties could be explored for both high and low surface coverages, which open a way for studies where interparticle interactions can be systematically controlled.
Highlights
Magnetic nanoparticles have shown great potential for applications in various technologies including drug delivery, bioimaging, and as building blocks for future high-performing permanent magnets.[1−4] The most common way of producing magnetic nanoparticles today is by multistep chemical methods
These measurements show that the magnetic properties could be explored for both high and low surface coverages, which open a way for studies where interparticle interactions can be systematically controlled
We demonstrate that it is possible to perform magnetic measurements with a superconducting quantum interference device (SQUID) on sparsely spaced deposited nanoparticles, separated with at least a few particle diameters, which opens a way for studies where interparticle interactions can be systematically studied
Summary
Magnetic nanoparticles have shown great potential for applications in various technologies including drug delivery, bioimaging, and as building blocks for future high-performing permanent magnets.[1−4] The most common way of producing magnetic nanoparticles today is by multistep chemical methods. We have demonstrated that, by adding a small amount of hydrogen to the carrier gas mixture, oxidation can be avoided for several elements during generation.[27] The excellent mixing possibilities in combination with controllable size, agglomeration, and purity make spark ablation combined with a compaction step a potential technique for future generation of complex magnetic nanoparticles. Based on closely examined individual particles, a discussion on the effects of the carrier gas and compaction temperature of bimetallic alloyed nanoparticles is added, which has not been performed earlier This knowledge is necessary in order to form monodisperse nanoparticles in a wider size range. The nanoparticles were deposited onto a quartz sample holder, and the measurements were performed using a Quantum Design MPMS3 vibrating sample magnetometer
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