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Controlled Oxidation and Self-Passivation of Bimetallic Magnetic FeCr and FeMn Aerosol Nanoparticles
journal contribution
posted on 2019-06-10, 00:00 authored by Calle Preger, Claudiu Bulbucan, Bengt O. Meuller, Linus Ludvigsson, Aram Kostanyan, Matthias Muntwiler, Knut Deppert, Rasmus Westerström, Maria E. MessingNanoparticle
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.