Z-STEM of L1_o Ordering in FePt Magnetic Nanoparticles

Conference · Mon Jan 01 04:00:00 EST 2007

OSTI ID:931754

Wittig, J. E. ^[1]; Bentley, James ^[2]; Lupini, Andrew R ^[2]; Lukehart, C. M. ^[1]

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1. Vanderbilt University
2. ORNL

The L1{sub o} (CuAuI) ordered FePt structure exhibits exceptional magnetic properties with uniaxial-magnetocrystalline anisotropy (K{sub u}) greater than 10{sup 6} ergs/cm3. Chemical synthesis methods can produce monodispersed FePt nanoparticles that have diameters ranging from 3 to 10 nm with a standard deviation of less than 5%. As-synthesized, the FePt nanoparticles are face-centered cubic (FCC) and require annealing at temperatures greater than 550 C for chemical ordering into the L1{sub o} structure. X-ray diffraction (XRD) methods typically characterize the ordering phase transformation by measuring the superlattice peaks. However, since the FePt nanoparticles coarsen during annealing, the larger particles may dominate the XRD data while the smallest particles correspondingly may contribute little to the diffracted intensity. Since recent data suggest that the FePt L1{sub o} ordering transformation is particle-size dependent, the current study employs high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM), also known as atomic-number contrast or Z-STEM, methods to investigate the presence of L1{sub o} order in individual FePt nanoparticles.

• Research Organization: Oak Ridge National Laboratory (ORNL); Shared Research Equipment Collaborative Research Center
• Sponsoring Organization: SC USDOE - Office of Science (SC); ORNL work for others
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 931754
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
FePt
IRON ALLOYS
MAGNETIC PROPERTIES
NANOSTRUCTURES
ORDER PARAMETERS
PHASE TRANSFORMATIONS
PLATINUM ALLOYS
STEM
atomic resolution
magnetism
nanoparticles
phase transformation