Magnetic, structural and microstructural properties of FePt/M (M=C,BN) granular films

Christodoulides, Joseph A.; Farber, P.; Dannl, M.; Okumura, Hideyuki; Hadjipanaysi, G.C.; Skumryev, V.; Simopoulos, A.; Weller, D.

doi:10.1109/20.950821

Cited by 118 publications

(57 citation statements)

References 9 publications

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“…For example, the chemical ordering parameters can be calculated by the equation S Х 0.85͑I 001 / I 002 ͒ 1/2 , where I hkl is the integrated intensity of ͑hkl͒ XRD peak of L1 0 -FePt nanoparticles. 11,23,24 For 8 nm L1 0 particles, S was found to increase from 0.88 to 0.92 as a result of the high-temperature annealing.…”

Section: Resultsmentioning

confidence: 99%

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

Rong

Poudyal

Chaubey

et al. 2008

Journal of Applied Physics

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Monodisperse L1 0 -FePt nanoparticles with size ranging from 3 to 8 nm were prepared by the salt-matrix annealing method. It was observed that the annealed particles have high thermal stability-no sintering occurred even when the particles were heated at 1100°C for an hour. This high thermal stability resulted from carbon coating of the particles during salt-matrix annealing as consequence of decomposition of surfactants.

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Section: Resultsmentioning

confidence: 99%

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

Rong

Poudyal

Chaubey

et al. 2008

Journal of Applied Physics

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“…Subscripts f and s indicate values for the fundamental and the superlattice reflections, respectively. 8,15,16 S of the 3 nm annealed particles is 0.62± 0.05 by the above formula. The error is estimated by the standard deviation based on four independent XRD measurements.…”

Section: ͑1͒mentioning

confidence: 96%

Structural phase transition and ferromagnetism in monodisperse 3 nm FePt particles

Rong

Poudyal

Chaubey

et al. 2007

Journal of Applied Physics

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FePt nanoparticles with a size of 3 nm and thermally stable room-temperature ferromagnetism are investigated. The monodisperse nanoparticles were prepared by chemical synthesis and a salt-matrix annealing technique. Structural and magnetic characterizations confirmed the phase transition from the disordered face-centered cubic structure to the L1 0 structure with the chemical ordering parameter of 0.62± 0.05. Analysis in blocking temperature and fitting of temperature dependence of switching field reveals that the transformed 3 nm nanoparticles have a magnetic anisotropy constant of ͑2.8± 0.2͒ ϫ 10 6 J/m 3 , smaller than those for the bigger particles and the fully ordered L1 0 bulk phase.

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“…To evaluate the effect of chemical ordering of the L1 0 phase in a quantitative way, the following equation was used to calculate the ordering parameter S [17][18][19] S ≅ 0:85…”

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Size‐Dependent Chemical and Magnetic Ordering in L1₀‐FePt Nanoparticles

et al. 2006

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FePt nanoparticles have great application potential in advanced magnetic materials such as ultrahigh-density recording media and high-performance permanent magnets. [1][2][3] The key for applications is the very high uniaxial magnetocrystalline anisotropy of the L1 0 -FePt phase, which is based on crystalline ordering of the face-centered tetragonal (fct) structure, described by the chemical-ordering parameter S.[4] Higher chemical ordering results in higher magnetocrystalline anisotropy. Unfortunately, as-synthesized FePt nanoparticles take a disordered face-centered cubic (fcc) structure that has low magnetocrystalline anisotropy. Heat-treatment is necessary to convert the fcc structure to the ordered fct structure. Several previous theoretical and experimental investigations have been reported on the size-dependent chemical ordering of FePt nanoparticles. [5][6][7][8][9] It has been observed that the degree of ordering decreases with decreasing particle size of the sputtered FePt nanoparticles. [5,6] Theoretical simulation predicted that the ordering would not take place when the particle size is below a critical value. [8,9] However, there have not been systematic experimental studies on quantitative size dependence of chemical ordering of FePt nanoparticles due to the lack of monodisperse L1 0 -FePt nanoparticles with controllable sizes.There are also few studies reported to date on the quantitative particle size dependence of magnetic properties, including the Curie temperature, coercivity, and magnetization of the L1 0 -FePt phase, although it has been well accepted that there is a size effect on the ferromagnetism of any low-dimensional magnets. [10,11] Additionally, the magnetic properties of FePt ferromagnets, as observed in thin-film samples, [4,12] are affected by the degree of chemical ordering, which is in turn size dependent. It is therefore highly desirable to understand the size and chemical-ordering effects, and their influence on the magnetic properties of the nanoparticles. A major hurdle in obtaining the particle size dependence of structural and magnetic properties of the L1 0 phase is particle sintering during heat-treatments that convert the fcc phase to the fct phase. [13,14] This long-pending problem has been solved recently by adopting the salt-matrix annealing technique. [15,16] With this technique, particle aggregation during the phase transformation has been avoided so that the true size-dependent properties of the fct phase can be measured. In this paper, we report results on quantitative particle size dependence of the chemical-ordering parameter S and selected magnetic properties, including the Curie temperature, T c , magnetization, M s , and coercivity, H c , with the particle size varying from 2 to 15 nm. Figure 1 shows the transmission electron microscopy (TEM) images of the FePt nanoparticles with different sizes before and after annealing in a salt matrix at 973 K for 4 h. The images, from left to right, show nanoparticles with nominal diameters of 2, 4, 6, 8, and 15 nm, res...

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Magnetic, structural and microstructural properties of FePt/M (M=C,BN) granular films

Cited by 118 publications

References 9 publications

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

Structural phase transition and ferromagnetism in monodisperse 3 nm FePt particles

Size‐Dependent Chemical and Magnetic Ordering in L1₀‐FePt Nanoparticles

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Magnetic, structural and microstructural properties of FePt/M (M=C,BN) granular films

Cited by 118 publications

References 9 publications

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

High thermal stability of carbon-coated L10-FePt nanoparticles prepared by salt-matrix annealing

Structural phase transition and ferromagnetism in monodisperse 3 nm FePt particles

Size‐Dependent Chemical and Magnetic Ordering in L10‐FePt Nanoparticles

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Size‐Dependent Chemical and Magnetic Ordering in L1₀‐FePt Nanoparticles