Structure and magnetic property changes of epitaxially grown L1₀-FePd isolated nanoparticles on annealing

Isolated 10-nm-sized FePd nanoparticles were fabricated by electron-beam evaporation and postannealing above 773 K. FePd particles were epitaxially grown on a cleaved NaCl(001) substrate and were two-dimensionally dispersed on the substrate. Results showed that coalescence and growth of the particles were not prominent during annealing, indicating that the alloying and atomic ordering reactions proceeded mostly within each nanoparticle.Kazuhisa Sato and Yoshihiko Hirotsu, "Structure and magnetic property changes of epitaxially grown L10-FePd isolated nanoparticles on annealing", Journal of Applied Physics 93, 6291-6298 (2003) https://doi.org/10.1063/1.1568531

Atomic ordering reation and associated variation of magnetic coercivity of oriented L1₀-Fept nanoparticles

Atomically ordered FePt nanoparticles (L10-type structure) covered with amorphous (a-) Al2O3 have been fabricated. In this process, Fe particles were deposited on Pt “seed” particles which were epitaxially grown on (100) NaCl or MgO substrates. Annealing the a-Al2O3/Fe/Pt films at temperatures higher than 773 K leads to a formation of ordered nanoparticles with mutual fixed orientation in a monolayer form. Three variant ordered domains of the tetragonal L10 structure coexisted in a single nm-sized FePt particle, even in a particle as small as 7 nm. According to in-situ electron diffraction study, the degree of order of the ordered structure started to increase on annealing at 773 K and almost saturated on annealing at 873 K for 16 h. The magnetic coercivity varied depending on the particle size and the degree of order in the L10 structure formation. The perpendicular coercivity exceeded the in-plane one during the annealing. The in-plane coercivities of FePt nanoparticles measured both parallel to [100]MgO and [010]MgO directions were almost equal in numerical value. These results reflect the ordered domain formation process and the volume fraction of the domains. Remanent magnetization decay measured for the in-plane magnetization revealed a magnetic relaxation with the type of magnetic dipolar interaction between the FePt particles

Fabrication of oriented L1₀-FeCuPd and composite bcc-FeL1₀-FeCuPd nanoparticles: Alloy composition dependence of magnetic properties

Oriented and well-isolated L 10 -FeCuPd ternary alloy nanoparticles have been fabricated by electron-beam evaporation followed by postdeposition annealing. A single L 10 phase was formed in the FeCuPd nanoparticles with (Fe+Cu) content lower than 48 at. %. A strong preferential c -axis orientation along the film normal direction was achieved by Cu addition, which leads to a strong perpendicular magnetic anisotropy. Also, a lowering of the ordering temperature by 50 K compared to the binary L 10 -FePd nanoparticles was achieved by Cu addition. By contrast, composite particles composed of the bcc Fe and the L 10 -FeCuPd were formed when the (Fe+Cu) content was higher than 52 at. %. Coexistence of the bcc Fe and the L 10 -FeCuPd was confirmed by high-resolution transmission electron microscopy and nanobeam electron diffraction. It was found that perpendicular magnetic anisotropy of the L 10 -FeCuPd nanoparticles on the NaCl substrate is sensitive to the alloy composition. © 2006 American Institute of Physics.Hiroshi Naganuma, Kazuhisa Sato, and Yoshihiko Hirotsu, "Fabrication of oriented L1₀-FeCuPd and composite bcc-Fe/L1₀-FeCuPd nanoparticles: Alloy composition dependence of magnetic properties", Journal of Applied Physics 99, 08N706 (2006) https://doi.org/10.1063/1.2165604

Fabrication of exchange-coupled α-Fe/L1₀-FePd nanocomposite isolated particles

The fabrication of exchange-coupled α-Fe/L10-FePd nanocomposite particles, by annealing the Fe/Pd nanocomplex particles, was analyzed. It was observed that two regions composed of α-Fe and L1 0-FePd coexisted in each nanoparticle separated by a diffusion boundary. It was also observed that there was a gradual increase in the saturation magnetization with increase in the volume ratio of the α-Fe region. The results show that an exchange coupling existed between α-Fe and L10-FePd crystallites connected coherently with each other within the nanoparticles.Junichi Kawamura, Kazuhisa Sato, and Yoshihiko Hirotsu, "Fabrication of exchange-coupled α-Fe/L1₀-FePd nanocomposite isolated particles", Journal of Applied Physics 96, 3906-3911 (2004) https://doi.org/10.1063/1.1782963

Strong perpendicular magnetic anisotropy of Fe-Pd nanocrystalline particles enhanced by Co addition

L1₀ -PdCoFe nanoparticles were prepared by vapor deposition of the components and characterized by transmission electron microscopy and by superconducting quantum interference device magnetometry. Co addition to the Fe-Pd nanocrystals resulted in a strong perpendicular magnetic anisotropy and a reduction in the formation temperature of the ordered L1₀ phase. Formation of the ordered phase was studied by in situ annealing of specimens inside the transmission electron microscope. L1₀ phase formation started at 698 K, as evidenced by the appearance of 110 superlattice reflections in electron diffraction patterns. Co additions enhanced the magnetic easy axis alignment perpendicular to the film plane. The perpendicular maximum coercivity at room temperature was 1.75 kOe for L1₀ -PdCoFe nanoparticles with an average size of 8 nm, and the magnetic coercivity decreased by increasing the Co concentration in the L1₀ nanoparticles. © 2007 American Institute of Physics.András Kovács, Kazuhisa Sato, and Yoshihiko Hirotsu, "Strong perpendicular magnetic anisotropy of Fe–Pd nanocrystalline particles enhanced by Co addition", Journal of Applied Physics 101, 033910 (2007) https://doi.org/10.1063/1.2434958

Perpendicular magnetic anisotropy of epitaxially grown L1₀-FePdCu nanoparticles with preferential c -axis orientation

Oriented and well-isolated 14-nm -sized Fe₄₁ Pd₅₂ Cu₇ ternary alloy nanoparticles with the L 1₀ -type ordered structure have been fabricated by the sequential deposition of Pd, Cu, and Fe on NaCl (001) substrate followed by postdeposition annealing. The annealing temperature required to obtain a high coercivity decreased by at least 50 K upon the addition of a small amount of Cu. Furthermore, it was revealed that a strong preferential c -axis orientation along the film normal direction was achieved by the addition of Cu, which resulted in a strong perpendicular magnetic anisotropy. The population of the nanoparticles with their c -axis oriented normal to the film plane was 74%. The alloy composition was independent of the particle size, as determined by energy dispersive x-ray spectroscopy using nanoprobe electrons. Nanobeam electron diffraction revealed that the axial ratio is constant for FePdCu nanoparticles with sizes between 10 and 25 nm. Interparticle magnetostatic and exchange interactions played an insignificant role in the isolated FePdCu nanoparticles. The correlation between their preferential c -axis orientation and magnetic properties is discussed based on the rotation magnetization of single magnetic domain particles. © 2006 American Institute of Physics.Hiroshi Naganuma, Kazuhisa Sato, and Yoshihiko Hirotsu, "Perpendicular magnetic anisotropy of epitaxially grown L1₀-FePdCu nanoparticles with preferential c-axis orientation", Journal of Applied Physics 100, 074914 (2006) https://doi.org/10.1063/1.2357420

Fabrication of oriented L1₀-FePt and FePd nanoparticles with large coercivity

Oriented L1 0-FePt and FePd nanoparticles with coercivities as large as 5 kOe (FePt) and 3 kOe (FePd) were fabricated by alternating deposition of Pt(or Pd) and Fe nanoparticles and their annealing at the temperatures between 773 and 873 K on single crystal NaCl and MgO. Atomic ordering reactions and degrees of order towards the L1 0-structure formation in these nanoparticles were investigated by high resolution electron microscopy and electron diffraction, and magnetic coercivities at low temperature were also measured. The long range order parameter of the FePt nanoparticles was ∼0.56 even after annealing at 873 K for 24 h. The coercivity of the FePt nanoparticles at 100 K was as high as twice the room temperature value. The low degree of order in the L1 0-structure formation and the thermal effect on magnetization have been found in the present FePt and FePd nanoparticles. These are closely concerned with the origin of the coercivity values which are very small in comparison with those expected from the single magnetic domain theory. © 2002 American Institute of Physics.Kazuhisa Sato, Bo Bian, and Yoshihiko Hirotsu, "Fabrication of oriented L10-FePt and FePd nanoparticles with large coercivity", Journal of Applied Physics 91, 8516-8518 (2002) https://doi.org/10.1063/1.1456446