Size effect ordering in $[FePt]100−xCrx$ nanoparticles

A series of $[FePt]100−xCrx$ nanoparticles (⁠$x=5$⁠, 10, and $16at.%$⁠) was chemically synthesized by two different techniques. In one method, the simultaneous chemical reduction of $FeCl2∙4H2O$⁠, Pt-acetylacetonate, and Cr-acetylacetonate was used with 2, 4 hexadecanediol as the reducing agent and phenyl ether as the solvent. The as-prepared particles had a mean size of $1.5nm$⁠. In the second method, the simultaneous chemical reduction of Pt-acetylacetonate and Cr-acetylacetonate and the thermal reduction of $Fe(CO)5$ were used with adamantanecarboxylic acid as the reducing agent and hexadecylamine as the solvent. These as-prepared particles were $3.5nm$ in size. X-ray diffraction confirmed that the Cr formed a solid solution within the $A1$ FePt phase for both processes. Upon annealing, the Cr hindered sintered grain growth of FePt nanoparticle arrays. Consequently, we were able to use Cr as a means to tune the ordering temperature as a function of the size effect in FePt nanoparticles. The presence of Cr in the ordered FePt reduced the magnetic coercivity of the transformed nanoparticles.