Reversible Modification of Magnetic Properties of Fe3C Nanoparticles by Chemisorption of CO

Synthesis and magnetic properties of sub-nanosized iron carbides on a carbon support

“…2 As with metallic iron, iron carbides are also known to exhibit ferromagnetism; 3,4 therefore, there have been many studies reported on the ferromagnetism of bulk iron carbides and iron carbide nanoparticles. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The size effect in nanomaterials is also of particular interest because the properties of the bulk materials can be signicantly changed. For example, melting-point depression, 20 catalyst activation, 21 and the alloying of non-mixable metals 22 have been reported to occur as the particle size decreases into the nanosize range.…”

“…† There are several reports for TEM observations of iron carbide nanoparticles larger than 2 nm diameter without atomic-resolution. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Very ne particles dispersed over the carbon support were observed as blurry black dots in the TEM images. The mean particle diameter and standard deviation of the size distribution were estimated to be 0.9 AE 0.2 nm (Fe 12 /C), 1.0 AE 0.3 nm (Fe 28 /C), and 1.3 AE 0.3 nm (Fe 60 /C), respectively.…”

“…Nanoparticle magnets have a single magnetic-domain structure and exhibit hysteresis at room temperature; however, they lose this hysteresis upon downsizing by superparamagnetism. There have been no reports of subnanoparticle magnets (diameter: $1 nm or less) that exhibit coercivity above room temperature; [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]49 neither for e.g. Fe-Pt bimetallic nanoparticles 50 nor iron oxide nanoparticles.…”