AVS 52nd International Symposium
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+NS-TuM

Paper MI+NS-TuM1
Size Effect and Chemical Ordering in [FePt]@sub 100-x@Cr@sub x@ Nanoparticles

Tuesday, November 1, 2005, 8:20 am, Room 204

Session: Magnetic Nanostructures, Surfaces, and Interfaces
Presenter: G.B. Thompson, University of Alabama
Authors: C. Srivastava, University of Alabama
G.B. Thompson, University of Alabama
J.W. Harrell, University of Alabama
D.E. Nikles, University of Alabama
Correspondent: Click to Email
FePt nanoparticles have received considerable attention as candidate materials for achieving ultra-high areal storage densities. Recent experimental and modeling studies have suggested that FePt must achieve a critical size near 4 nm for the chemically ordered L1@sub 0@ phase to be stable. We report the use of Cr in controlling the size and ordering temperature in FePt nanoparticles. Two series of [FePt]@sub 100-x@Cr@sub x@ nanoparticles (x = 5, 10 and 16 at. %) were chemically synthesized by a high-temperature salt-decomposition process yielding as-prepared diameters of 2 nm and 4 nm. XRD and STEM-EDS confirmed that the Cr formed a solid solution within the A1 FePt phase. Upon annealing, the as-synthesized 4 nm [FePt]@sub 100-x@Cr@sub x@ particles ordered at 450°C while maintaining ~4 nm size. In contrast, the as-synthesized 2 nm [FePt]@sub 100-x@Cr@sub x@ particles ordered at 550°C. It was noted that the initial 2 nm particles had achieved an ~4 nm sintered particle size at 550°C. Thus, the initial particle size is critical before chemical ordering can commence. Once the critical size is achieved, Cr was able to reduce the ordering temperature. The initial 4 nm FePt nanoparticles ordered at ~500°C and experienced rapid particle sintering at the onset of its ordering temperature. In contrast, the Cr alloyed nanoparticles were shown to have reduced grain growth at elevated temperatures. Magnetrometry measurements of the nanoparticles indicated that the coercivity is reduced with Cr content.