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Published on: February 11, 2018
Discrete, dispersible MnAs nanocrystals from solution methods: phase control on the nanoscale and magnetic
Keerthi Senevirathne1, Ronald Tackett, Parashu Ram Kharel
1Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
ACS Nano
|April 11, 2009
Summary
Synthesized manganese arsenide (MnAs) nanocrystals exhibit unique core-shell structures and intrinsic ferromagnetism. Unlike bulk materials, these nanoparticles maintain their ferromagnetic properties across phase transitions, offering new avenues for materials science research.
Area of Science:
- Materials Science
- Nanotechnology
- Solid State Physics
Background:
- Manganese arsenide (MnAs) exists in two forms: stable alpha-MnAs and metastable beta-MnAs.
- Bulk MnAs exhibits a phase transition from ferromagnetic alpha- to paramagnetic beta- phase around 313-317 K.
- Previous synthesis methods often resulted in supported or non-dispersible MnAs structures.
Purpose of the Study:
- To synthesize discrete, dispersible MnAs nanocrystals using a bottom-up approach.
- To investigate the structural, phase, and magnetic properties of alpha- and beta-MnAs nanocrystals.
- To compare the behavior of MnAs nanocrystals with their bulk counterparts.
Main Methods:
- Synthesis of alpha- and beta-MnAs nanocrystals via reaction of triphenylarsine oxide and dimanganese decacarbonyl in trioctylphosphine oxide at 250-330 °C.
- Morphological analysis using electron microscopy to identify core-shell structures.
- Powder X-ray diffraction to study phase stability and lattice parameters.
- Magnetic measurements to determine ferromagnetic properties and Curie temperature (T(C)).
Main Results:
- Successfully synthesized discrete, dispersible alpha- and beta-MnAs nanocrystals with core-shell morphology.
- Nanocrystals showed reduced lattice parameters and volume compared to bulk MnAs, even without epitaxial strain.
- Powder X-ray diffraction indicated no alpha- to beta-MnAs conversion between 298-343 K.
- Both alpha- and beta-MnAs nanocrystals demonstrated ferromagnetism with T(C) approximately 315 K.
- Slow room-temperature transformation of beta- to alpha-MnAs occurred over months, without altering magnetization.
Conclusions:
- Bottom-up synthesis yields unique, dispersible MnAs nanocrystals with distinct properties from bulk.
- The observed ferromagnetism in beta-MnAs nanocrystals is intrinsic and not due to alpha-MnAs impurities.
- MnAs nanocrystals offer a new platform for exploring magnetic and phase transition phenomena in nanomaterials.
