Статті в журналах: "Ordered L10-FePt phase"

1

Tamura, Shota, Zhazgul Kelgenbaeva, Kenta Yamamoto, Li Liang Chen, and Tsutomu Mashimo. "Preparation of FePt Nanoparticles by Pulsed Plasma in Liquid Method." Key Engineering Materials 730 (February 2017): 248–52. http://dx.doi.org/10.4028/www.scientific.net/kem.730.248.

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FePt alloys are an important class of materials in permanent magnetic applications because of their large uniaxial magnetocrystalline anisotropy and good chemical stability. We have applied the pulsed plasma in liquid method to synthesis nanoparticles. Short duration of pulse and quenching effects of the surrounding liquid limit the size of crystal. That enable synthesis of small size and metastable nanoparticles. In this study, ferromagnetic FePt nanoparticles were successfully synthesized. Face-centered-cubic (FCC) A1-type phase was synthesized from FePt (Fe:PT=50:50, 55:45 in atomic %) alloy rod electrodes using the pulsed plasma in ethanol. The ordered face-centered-tetragonal (FCT) L10-type phase FePt was obtained by annealing the A1-type phase at 400oC for 1 h. The average diameter of L10-type FePt nanoparticles was less than 10 nm. Vibrating Sample Magnetometer (VSM) analysis showed that the coercivity of L10-type nanoparticles was much larger than that of the A1-type phase nanoparticles.

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2

Stappert, Sonja, Bernd Rellinghaus, Mehmet Acet, and Eberhard F. Wassermann. "Gas-phase preparation of L10 ordered FePt nanoparticles." Journal of Crystal Growth 252, no. 1-3 (May 2003): 440–50. http://dx.doi.org/10.1016/s0022-0248(03)00935-7.

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3

Makushko, P. V., M. N. Shamis, N. Y. Schmidt, I. E. Kotenko, S. Gulyas, G. L. Katona, T. I. Verbytska, D. L. Beke, M. Albrecht, and Iu M. Makogon. "Formation of ordered L10-FePt phase in FePt–Ag thin films." Applied Nanoscience 10, no. 12 (September 18, 2020): 4809–16. http://dx.doi.org/10.1007/s13204-020-01552-2.

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4

Jang, Tae Suk, J. H. Yu, D. W. Lee, and B. K. Kim. "Characterization of FePt Nanopowder Synthesized by a Chemical Vapor Condensation (CVC) Process." Materials Science Forum 638-642 (January 2010): 1708–13. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.1708.

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FePt binary alloy nanopowder has been synthesized by a chemical vapor condensation process using a mixture of iron acetylacetonate and platinum acetylacetonate. Particle size of the synthesized powder was less than 10 nm and the powder had very narrow size distribution with relatively high dispersivity. FePt nanopowder possessing L10 ordered phase was synthesized at the condition of well controlled precursor mixing ratio and reaction temperature with some disordered cubic phase.

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5

Ciprian, R., M. Carbucicchio, and G. Turilli. "Exchange-spring magnets based on L10-FePt ordered phase." Hyperfine Interactions 191, no. 1-3 (April 1, 2009): 33–40. http://dx.doi.org/10.1007/s10751-009-9981-0.

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6

Vladymyrskyi, Igor A., Anna I. Oleshkevych, S. I. Sidorenko, and Yurii N. Makogon. "FePt Thin Films – Prospective Materials for Ultrahigh Density Magnetic Recording." Journal of Nano Research 39 (February 2016): 151–61. http://dx.doi.org/10.4028/www.scientific.net/jnanor.39.151.

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Constant increase of magnetic recording density requires application of modern ferromagnetic materials with high value of magnetic anisotropy constant and coercivity. Thin films on the bases of L10-FePt ordered phase is one of such materials. However, practical application of such materials requires to solve a number of materials science problems such as decrease of ordered phase formation temperature, formation of its predominantly oriented grains and increase of coercivity. Factors that affect structure formation and properties of FePt based films have been examined in this study. A number of modern studies aimed on solving problems mentioned above have been analyzed.

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7

Sui, Yang, Zi Yu Chen, Xiao Lin Shu, and Tian Min Wang. "Point Defects in L1₀ Phase FePt Alloy: A First Principle Study." Materials Science Forum 561-565 (October 2007): 1923–26. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.1923.

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L10 phase FePt alloy is regarded as one of the most promising materials for ultra high density magnetic recording media. However, structural point defects, which would reduce the media's signal to noise ratio, are inevitable in non-stoichiometric L10 FePt alloy. Hence, possible types of point defect (vacancy and anti-site defect) in non-stoichiometric ordered FePt alloy were fully studied using density functional theory. Investigation over vacancy shows the formation energy of Fe and Pt vacancy is respectively 2.58eV and 3.20eV. Geometry relaxation implies Fe vacancy has a stronger deformation force upon the original lattice. Meanwhile, anti-site defect study shows that the formation energy of Fe anti-site (Fe occupation in Pt sublattice) and Pt anti-site (Pt occupation in Fe sublattice) is respectively 1.05eV and 0.66eV. Therefore, for Fe-rich and Pt-rich alloy, the preferred structural point defects are both anti-site substitution rather than vacancy due to the much lower formation energy.

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8

Tsoufis, Theodoros, Aphrodite Tomou, Dimitrios Gournis, Alexios P. Douvalis, Ioannis Panagiotopoulos, Bart Kooi, Vasilios Georgakilas, Imad Arfaoui, and Thomas Bakas. "Novel Nanohybrids Derived from the Attachment of FePt Nanoparticles on Carbon Nanotubes." Journal of Nanoscience and Nanotechnology 8, no. 11 (November 1, 2008): 5942–51. http://dx.doi.org/10.1166/jnn.2008.18366.

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Multiwalled carbon nanotubes (MWCNTs) were used as nanotemplates for the dispersion and stabilization of FePt nanoparticles (NPs). Pre-formed capped FePt NPs were connected to the MWCNTs external surface via covalent binding through organic linkers. Free FePt NPs and MWCNTs-FePt hybrids were annealed in vacuum at 700 °C in order to achieve the L10 ordering of the FePt phase. Both as prepared and annealed samples were characterized and studied using a combination of experimental techniques, such as Raman and Mössbauer spectroscopies, powder X-ray Diffraction (XRD), magnetization and transmittion electron microscopy (TEM) measurements. TEM measurements of the hybrid sample before annealing show that a fine dispersion of NPs along the MWCNTs surface is achieved, while a certain amount of free particles attached to each other in well connected dense assemblies of periodical or non-periodical particle arrangements is also observed. XRD measurements reveal that the FePt phase has the face-centered cubic (fcc) disordered crystal structure in the as prepared samples, which is transformed to the face-centered tetragonal (fct) L10 ordered crystal structure after annealing. An increase in the average particle size is observed after annealing, which is higher for the free NPs sample. Superparamagnetic phenomena due to the small FePt particle size are observed in the Mössbauer spectra of the as prepared samples. Mössbauer and magnetization measurements of the MWCNTs-FePt hybrids sample reveal that the part of the FePt particles attached to the MWCNTs surface shows superparamagnetic phenomena at RT even after the annealing process. The hard magnetic L10 phase characteristics are evident in the magnetization measurements of both samples after annealing, with the coercivity of the hybrid sample over-scaling that of the free NPs sample by a factor of 1.25.

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9

Zhang, Luran, Xinchen Du, Hongjie Lu, Dandan Gao, Huan Liu, Qilong Lin, Yongze Cao, Jiyang Xie, and Wanbiao Hu. "Influence of Cu on the Improvement of Magnetic Properties and Structure of L10 FePt Nanoparticles." Nanomaterials 11, no. 5 (April 23, 2021): 1097. http://dx.doi.org/10.3390/nano11051097.

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L10 ordered FePt and FePtCu nanoparticles (NPs) with a good dispersion were successfully fabricated by a simple, green, one-step solid-phase reduction method. Fe (acac)3, Pt (acac)2, and CuO as the precursors were dispersed in NaCl and annealed at different temperatures with an H2-containing atmosphere. As the annealing temperature increased, the chemical order parameter (S), average particle size (D), coercivity (Hc), and saturation magnetization (Ms) of FePt and FePtCu NPs increased and the size distribution range of the particles became wider. The ordered degree, D, Hc, and Ms of FePt NPs were greatly improved by adding 5% Cu. The highest S, D, Hc, and Ms were obtained when FePtCu NPs annealed at 750 °C, which were 0.91, 4.87 nm, 12,200 Oe, and 23.38 emu/g, respectively. The structure and magnetic properties of FePt and FePtCu NPs at different annealing temperatures were investigated and the formation mechanism of FePt and FePtCu NPs were discussed in detail.

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10

Abdank-Kozubski, Rafal, Andrzej Biborski, Mirosław Kozłowski, Christine Goyhenex, Veronique Pierron-Bohnes, Mebarek Alouani, Marcus Rennhofer, and Savko Malinov. "Atomic-Migration-Controlled Processes in Intermetallics." Defect and Diffusion Forum 277 (April 2008): 113–18. http://dx.doi.org/10.4028/www.scientific.net/ddf.277.113.

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Chemical ordering kinetics in L10- and B2-ordered AB binary intermetallics was simulated by means of Monte Carlo (MC) technique implemented with vacancy mechanism of atomic migration. While vacancy concentration is usually much lower than the antisite defect concentration in L10-ordered systems, triple defects are generated in particular B2–ordered systems. The latter definitely affects the chemical ordering process and requires that full thermal vacancy thermodynamics is involved in B2-ordering simulations. The study on L10-ordered binaries was dedicated to FePt thin layers considered as a material for ultra-high-density magnetic storage media. Metastability of the L10 c-variant with monoatomic planes parallel to the layer surface and off-plane easy magnetization was revealed. Thermal vacancy formation in B2-ordered binaries was modelled by implementing a mean-field Hamiltonian with a specific formalism of phase equilibria in a latticegas composed of atoms and vacancies. It was demonstrated that for particular pair-interaction energetics, equilibrium concentrations of vacancies and antisites result mutually proportional in well-defined temperature ranges. The MC simulations of B2-ordering kinetics involved the modelled equilibrium vacancy concentration and reproduced the experimentally observed low rate of the process.

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11

Li, Cui Xia, Zhi Hong Li, Xue Yan Du, and Hai Xia Guo. "Synthesis and Magnetic Properties of FePt /Silica Core-Shell Nanoparticles." Advanced Materials Research 178 (December 2010): 291–95. http://dx.doi.org/10.4028/www.scientific.net/amr.178.291.

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FePt nanoparticles (NPS), ~2nm in diameter, were synthesized and then coated with silica (SiO2) shells ~1.5nm-thick using reverse micelles as nanoreactors. The silica-coated FePt core–shell (FePt @silica) NPS were characterized by direct techniques of transmission electron microscopy (TEM). The results showed that the silica shells prevented the aggregation in liquid comparing to their bare counterparts. The as-synthesized FePt@SiO2 NPS exhibited essential characteristics of superparamagnetic behavior, as investigated by a vibrating sample magnetometer (VSM). X-ray diffraction (XRD) studies proved that the annealing at 700 °C for 30min under argon atmosphere caused the crystal structure of FePt core to transform from disordered face centered cubic (fcc) to the chemically ordered L10 FePt with face-centered tetragonal (fct) structure. This phase transition caused the change of magnetic properties of the FePt@SiO2 particles from superparamagnetism to ferromagnetism.

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12

Wiezorek, Jörg M. K. "Cold-Working and Annealing of L1₀-Ordering Iron-Palladium Base Intermetallics." Materials Science Forum 539-543 (March 2007): 1487–94. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1487.

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Alloys based on FePd in the vicinity of the equiatomic composition are good model systems to study the microstructrual and phase transformation behavior of the class of technologically interesting ferromagnetic L10-intermetallics that includes also FePt and CoPt. Here, thermo-mechanical processing, involving cold-work and annealing at temperatures below the ordering temperature was used to control microstructures and to improve properties of FePd. L10- ordered FePd with ultra-fine grain sizes and up to about 8-fold increased coercivity compared with conventionally processed material has been obtained. Relationships between processing condition, microstructure (scale, morphology and texture) and the magnetic properties are discussed.

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13

Qiu, Jiao-Ming, and Jian-Ping Wang. "Monodispersed and highly ordered L10 FePt nanoparticles prepared in the gas phase." Applied Physics Letters 88, no. 19 (May 8, 2006): 192505. http://dx.doi.org/10.1063/1.2202130.

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14

Ohmori, Kazuhiko, Tomonori Umeda, Takuya Sakaguchi, Masaaki Doi, Pan Huayong, Hidefumi Asano, Nobuo Tanaka, and Masaaki Matsui. "Magnetic Properties of Fe-Pt Nanoparticle Protected by PVP Polymer." Materials Science Forum 475-479 (January 2005): 2131–34. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.2131.

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Annealing effect on the magnetic properties of Fe-Pt nanoparticle was investigated. Fe-Pt nanoparticles were synthesized by the chemical reduction of H2PtCl6 and the decomposition of Fe(CO)5 in the presence of PVP polymers. The samples were annealed at several temperatures from 350°C to 600°C and the structural and magnetic properties were studied by TEM, XRD and magnetization measurements. FePt nanoparticles as-synthesized showed super-paramagnetism and annealed samples at temperatures more than 400°C, ferromagnetism. The crystal structure of as-synthesized sample was disordered fcc, but chemically ordered fct, when it was annealed at more than 400°C. The annealing effects are the concatenation or agglomeration of nanoparticles accompanied with the increase in particle diameter and with the ordering of the FePt superlattice. The critical diameter for emergence of ferromagnetism of FePt particle has been considered to be 3.6 to 5.6 nm in mean diameter, under the existence of the ordered L10 phase The blocking temperature as a function of the annealing temperature was investigated.

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15

Liu, Xiaoqi, and Jian-Ping Wang. "Fabrication and morphologies of large directly ordered L10 FePt nanoparticles in gas phase." Journal of Applied Physics 105, no. 7 (April 2009): 07A722. http://dx.doi.org/10.1063/1.3067847.

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16

Chen, S. C., T. H. Sun, and Po Cheng Kuo. "Effect of Annealing on Magnetic Properties and Domain Structures of FePt Thin Films by Rapid Thermal Annealing Technique." Advanced Materials Research 79-82 (August 2009): 911–14. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.911.

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Single-layered FePt films of 30 nm thick were annealed at temperature between 300 and 800 °C for 1–180 sec by a rapid thermal annealing (RTA) with a high heating rate of 100 °C/sec. It is found that both the grain size and magnetic domain size of the FePt film increase with increasing annealing temperature and annealing time. The FePt films exhibited soft magnetic properties and without domain images were observed by magnetic force microscope (MFM) when the films were post-annealed at below 500 °C for 180 sec. The in-plane coercivity (Hc//) and perpendicular coercivity (Hc⊥) of FePt film increases significantly to 7.5 and 6.5 kOe respectively as annealing temperature increases to 600 °C. When the annealing temperature is increased to 700 °C, they are increased to 11.1 and 9.5 kOe, respectively, and the domain structure inclines to isolated domain. However, further increasing the annealing temperature to 800 °C, the Hc// and Hc⊥ values decrease to 9.8 and 8.9 kOe respectively due to largely increase the grain size of FePt and change the domain structure from isolation to continuity. On the other hand, in order to transform the FePt film from disordered γ phase to the ordered L10 phase, the annealing time of over 3 seconds is necessary when the film was post-annealed at 700 °C with a high heating rate of 100 °C/sec by RTA technique.

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17

Tzitzios, Vasileios, Georgia Basina, Nikolaos Tzitzios, Vasileios Alexandrakis, Xiaocao Hu, and George Hadjipanayis. "Direct liquid phase synthesis of ordered L10 FePt colloidal particles with high coercivity using an Au nanoparticle seeding approach." New Journal of Chemistry 40, no. 12 (2016): 10294–99. http://dx.doi.org/10.1039/c6nj01801g.

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18

Zhao, Z. L., J. Ding, K. Inaba, J. S. Chen, and J. P. Wang. "Promotion of L10 ordered phase transformation by the Ag top layer on FePt thin films." Applied Physics Letters 83, no. 11 (September 15, 2003): 2196–98. http://dx.doi.org/10.1063/1.1611280.

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19

Schilling, Martin, Paul Ziemann, Zaoli Zhang, Johannes Biskupek, Ute Kaiser, and Ulf Wiedwald. "Orientation of FePt nanoparticles on top of a-SiO2/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size." Beilstein Journal of Nanotechnology 7 (April 21, 2016): 591–604. http://dx.doi.org/10.3762/bjnano.7.52.

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Texture formation and epitaxy of thin metal films and oriented growth of nanoparticles (NPs) on single crystal supports are of general interest for improved physical and chemical properties especially of anisotropic materials. In the case of FePt, the main focus lies on its highly anisotropic magnetic behavior and its catalytic activity, both due to the chemically ordered face-centered tetragonal (fct) L10 phase. If the c-axis of the tetragonal system can be aligned normal to the substrate plane, perpendicular magnetic recording could be achieved. Here, we study the orientation of FePt NPs and films on a-SiO2/Si(001), i.e., Si(001) with an amorphous (a-) native oxide layer on top, on MgO(001), and on sapphire(0001) substrates. For the NPs of an approximately equiatomic composition, two different sizes were chosen: “small” NPs with diameters in the range of 2–3 nm and “large” ones in the range of 5–8 nm. The 3 nm thick FePt films, deposited by pulsed laser deposition (PLD), served as reference samples. The structural properties were probed in situ, particularly texture formation and epitaxy of the specimens by reflection high-energy electron diffraction (RHEED) and, in case of 3 nm nanoparticles, additionally by high-resolution transmission electron microscopy (HRTEM) after different annealing steps between 200 and 650 °C. The L10 phase is obtained at annealing temperatures above 550 °C for films and 600 °C for nanoparticles in accordance with previous reports. On the amorphous surface of a-SiO2/Si substrates we find no preferential orientation neither for FePt films nor nanoparticles even after annealing at 630 °C. On sapphire(0001) supports, however, FePt nanoparticles exhibit a clearly preferred (111) orientation even in the as-prepared state, which can be slightly improved by annealing at 600–650 °C. This improvement depends on the size of NPs: Only the smaller NPs approach a fully developed (111) orientation. On top of MgO(001) the effect of annealing on particle orientation was found to be strongest. From a random orientation in the as-prepared state observed for both, small and large FePt NPs, annealing at 650 °C for 30 min reorients the small particles towards a cube-on-cube epitaxial orientation with a minor fraction of (111)-oriented particles. In contrast, large FePt NPs keep their as-prepared random orientation even after doubling the annealing period at 650 °C to 60 min.

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20

Crisan, O., I. Dan, P. Palade, A. D. Crisan, A. Leca, and A. Pantelica. "Magnetic Phase Coexistence and Hard–Soft Exchange Coupling in FePt Nanocomposite Magnets." Nanomaterials 10, no. 8 (August 18, 2020): 1618. http://dx.doi.org/10.3390/nano10081618.

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With the aim of demonstrating phase coexistence of two magnetic phases in an intermediate annealing regime and obtaining highly coercive FePt nanocomposite magnets, two alloys of slightly off-equiatomic composition of a binary Fe-Pt system were prepared by dynamic rotation switching and ball milling. The alloys, with a composition Fe53Pt47 and Fe55Pt45, were subsequently annealed at 400 °C and 550 °C and structurally and magnetically characterized by means of X-ray diffraction, 57Fe Mössbauer spectrometry and Superconducting Quantum Interference Device (SQUID) magnetometry measurements. Gradual disorder–order phase transformation and temperature-dependent evolution of the phase structure were monitored using X-ray diffraction of synchrotron radiation. It was shown that for annealing temperatures as low as 400 °C, a predominant, highly ordered L10 phase is formed in both alloys, coexisting with a cubic L12 soft magnetic FePt phase. The coexistence of the two phases is evidenced through all the investigating techniques that we employed. SQUID magnetometry hysteresis loops of samples annealed at 400 °C exhibit inflection points that witness the coexistence of the soft and hard magnetic phases and high values of coercivity and remanence are obtained. For the samples annealed at 500 °C, the hysteresis loops are continuous, without inflection points, witnessing complete exchange coupling of the hard and soft magnetic phases and further enhancement of the coercive field. Maximum energy products comparable with values of current permanent magnets are found for both samples for annealing temperatures as low as 500 °C. These findings demonstrate an interesting method to obtain rare earth-free permanent nanocomposite magnets with hard–soft exchange-coupled magnetic phases.

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21

Ristau, R. A., K. Barmak, L. H. Lewis, K. R. Coffey, and J. K. Howard. "On the relationship of high coercivity and L10 ordered phase in CoPt and FePt thin films." Journal of Applied Physics 86, no. 8 (October 15, 1999): 4527–33. http://dx.doi.org/10.1063/1.371397.

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22

Kang, Eunae, Hyunok Jung, Je-Geun Park, Seungchul Kwon, Jongmin Shim, Hiroaki Sai, Ulich Wiesner, Jin Kon Kim, and Jinwoo Lee. "Block Copolymer Directed One-Pot Simple Synthesis of L10-Phase FePt Nanoparticles inside Ordered Mesoporous Aluminosilicate/Carbon Composites." ACS Nano 5, no. 2 (January 12, 2011): 1018–25. http://dx.doi.org/10.1021/nn102451y.

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23

Verbitskaya, T. I., E. V. Figurnaya, M. Yu Verbitskaya, I. A. Vladymyrskyi, S. I. Sidorenko, E. P. Pavlova, and Yu N. Makogon. "Effect of Copper on the Formation of Ordered L10(FePt) Phase in Nanosized Fe50Pt50/Cu/Fe50Pt50 Films on SiO2/Si (001) Substrates." Powder Metallurgy and Metal Ceramics 55, no. 1-2 (May 2016): 109–13. http://dx.doi.org/10.1007/s11106-016-9785-0.

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24

Goyhenex, Christine, R. V. P. Montsouka, Mirosław Kozłowski, and Veronique Pierron-Bohnes. "Interdiffusion of Two L1₀Phases without Long-Range Order Decrease: Experiments and Molecular Dynamics Simulations." Solid State Phenomena 129 (November 2007): 59–66. http://dx.doi.org/10.4028/www.scientific.net/ssp.129.59.

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The L10 ordered MPt(001) thin films (M = Fe or Co) are very interesting for perpendicular recording due to their magnetic anisotropy and magneto-optical behaviours. Epitaxial L10-ordered NiPt(001) / FePt(001) bi-layers were co-deposited on MgO(100) substrates by MBE. The L10 order parameter is high with the concentration modulation along the growth direction. Some FeNiPt2(001) thin films were obtained by interdiffusion of the bilayers. The long-range-order parameter is conserved after interdiffusion (S = 0.75 ± 0.06), which can be explained by different mechanisms: a second-neighbour jump, a six-jump cycle, an anti-structural bridge mechanism or an antisite-pair elimination and creation mechanism, a double vacancy or a triple defect diffusion mechanism. Quenched molecular dynamics calculations in the frame of the second moment approximation of the tight binding method have been performed to obtain the energetic paths of the different mechanisms. The secondneighbour vacancy jump, the simultaneous jumps of bivacancies and the triple defect mechanisms can be ruled out for energetic reasons.

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25

Huang, Y. H., J. Wan, Y. Zhang, G. C. Hadjipanayis, and D. Weller. "Fabrication of FePt/M (M=C, Ag) Nanoparticulate Thin Films with Perpendicular Anisotropy." MRS Proceedings 853 (2004). http://dx.doi.org/10.1557/proc-853-i5.1.

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ABSTRACTMagnetic nanoparticles with perpendicular anisotropy are attractive for applications in high-density recording media. For these applications, it is highly desirable to have particles with a size below 8 nm, a uniform size distribution, and a reduced ordering temperature to avoid unwanted particle agglomeration upon the required heat treatment to obtain the high anisotropy ordered L10 structure. In this work, FePt nanoparticles embedded in non-magnetic matrices M (M=C, Ag) have been fabricated by sputtering FePt and M multilayered thin films onto single crystal MgO [100] substrates at elevated temperatures up to 650 °C. The transformation from the disordered fcc to the ordered L10 phase in FePt nanoparticles was observed at temperatures as low as 300 °C. Besides the reduced transformation temperature, the deposited material showed an improved [001] texture for FePt/Ag thin films as compared to FePt/C due to lattice parameter matching between Ag and FePt. As the deposition temperature increases, the degree of atomic ordering approaches that of the fully ordered phase as indicated by the shift in the [002] XRD peak. TEM images showed that isolated particles with smaller average particle size (around 7 nm) were formed when the thickness of sputtered film is less than 4 nm. However, with a further increase of thickness of sputtered FePt film, a continuous layer of FePt particles was observed and the coercivity decreased rapidly due to a domain wall motion mechanism.

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26

Nakanishi, Masatoshi, Gen-ichi Furusawa, Kokichi Waki, Yasushi Hattori, Takeo Kamino, Katsuhiro Sasaki, Kotaro Kuroda, and Hiroyasu Saka. "In Situ HREM Observation of Phase Transformation Process in FePt and FePtCu Nanoparticles." MRS Proceedings 907 (2005). http://dx.doi.org/10.1557/proc-0907-mm05-04.

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AbstractThe processes of phase transformation in individual nanoparticles of FePt and FePtCu synthesized by the reverse micelle method, which are chemically homogeneous and monodisperse, have been investigated by an in-situ HREM observation in a FE-TEM. Polycrystalline FePt particles, initially of chemically disordered face-centered cubic phase (A1) were reconstructed into A1 single crystals between 25 °C and 650 °C, followed by phase transformation from A1 to chemically ordered face-centered tetragonal phase (L10) which began between 650 °C and 680 °C. The coalescence began concurrently with phase transformation, i. e., between 650 °C and 680 °C. They turned to be a round-shaped L10 particle between 680 °C and 720 °C. The single crystal formation, the phase transformation from A1 to L10, the coalescence and the round-shaped particle formation were also observed in the FePtCu nanoparticles. The temperatures of single crystal formation, phase transformation (and coalescence) and round-shaped particle formation of the FePtCu nanoparticles were between 25 °C and 500 °C, between 550 °C and 600 °C and between 600 °C and 650 °C, respectively. These temperatures were substantially lower than those for the FePt nanoparticles.

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27

Lai, Chih-Haung, Sheng-Huang Huang, Cheng-Han Yang, C. C. Chiang, S. H. Liou, D. J. Sellmyer, M. L. Yan, L. Yuan, and T. Yokata. "Effects of ion-beam irradiation on the L10 phase transformation and their magnetic properties of FePt and PtMn films (Invited)." MRS Proceedings 887 (2005). http://dx.doi.org/10.1557/proc-0887-q07-05.

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ABSTRACTIon-beam irradiation shows enhancement or degradation of magnetic properties on L10 phase of FePt and PtMn films. A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The in-plane coercivity greater than 5700 Oe can be obtained after disordered FePt films were irradiated at the beam current of several μA/cm2 with the ion does of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230°C. The comparison has been made on the [Fe/Pt]10/C films by RTA and high current-density He irradiation. Although RTA and ion irradiation both reach high coercivity, ion irradiation seems to suppress the (001) texture, leading to isotropic Hc. Ion-beam irradiation can also be applied to the transformation of PtMn. An ordered PtMn phase, a large exchange field and a high GMR ratio (11%) were obtained in PtMn-based spin valves by using 1.25 μA/cm2 He-ions. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and GMR of PtMn-based spin valves, respectively. We propose a novel approach to achieve magnetic patterning by using ion irradiation, which can be applied for patterned media and magnetic sensors.

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Miyata, Mai, Kyosuke Kishida, Katsushi Tanaka, and Haruyuki Inui. "Synthesis of Magnetic Nanoparticles by Sputtering." MRS Proceedings 980 (2006). http://dx.doi.org/10.1557/proc-980-0980-ii05-45.

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AbstractThe influence of experimental condition on morphology of FePt and Sm-Co nanoparticles synthesized by sputtering in a relatively high gas pressure has been studied. The sputtering apparatus is equipped with an annealing furnace that enables pre-deposition annealing of the nanoparticles. The effect of the annealing temperature on the ordering to the L10 FePt nanoparticles was also investigated. The morphology of the particles depends on a gas pressure and gas flow rate, but the sensitivity to experimental condition differs between FePt and Sm-Co. The morphology and domain structure of FePt nanoparticle are relatively the same in a wide range of experimental condition, whereas those of Sm-Co nanoparticle are significantly changed by variation of a gas pressure. FePt nanoparticles annealed in the annealing furnace prior to their deposition onto the substrate have the ordered L10 phase, which has an advantage for producing a magnetic recording media.

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29

Berry, David C., and Katayun Barmak. "L10 Ordered Intermetallics for Ultrahigh Density Magnetic Recording Media: Phase Formation and the Role of Alloy Chemistry and Composition." MRS Proceedings 980 (2006). http://dx.doi.org/10.1557/proc-980-0980-ii03-05.

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AbstractIn this paper we provide a summary review of our research regarding the effect of composition on the A1 to L10 transformation in binary FePt with compositions in the range of 39.3 to 55.3 at.% Pt and ternary FeCuPt alloys with Cu additions in the range of 1.0 to 19.4 at.%. These binary and ternary alloy films have been studied using non-isothermal differential scanning calorimetry (DSC) combined with the calculation of TTT diagrams generated via experimentally validated Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Composition is found to play a significant role in the transformation kinetics in both FePt and FeCuPt. However, when comparing equivalent FePt and FeCuPt alloys, the addition of Cu has no significant effect. TTT diagrams show that as little as a 90 °C increase in peak temperature from the DSC measurements can result in a >300× increase in the time required for full transformation using isothermal anneals. Our results on the effect of Cu additions are compared with those reported in the literature.

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30

Wen, Zunhong, Yanglin Wang, Cong Wang, Min Jiang, Hongxiao Li, Yuping Ren, and Gaowu Qin. "Redetermination of the Fe–Pt phase diagram by using diffusion couple technique combined with key alloys." International Journal of Materials Research, April 13, 2022. http://dx.doi.org/10.1515/ijmr-2021-8496.

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Abstract Fe–Pt intermetallic nanocrystals exhibit good chemical stability and unique magnetic and catalytic properties. However, there are still some discrepancies with regard to the order–disorder transitions of Fe–Pt phases, and experimental works reported for the phase equilibria of Fe–Pt alloys at low temperatures are scarce. Therefore, in this work, the phase equilibria and phase transformations of Fe–Pt alloys were systematically studied by using the diffusion couple technique combined with key alloys through electron probe microanalysis, X-ray diffraction and differential scanning calorimetry. As a result, the composition ranges of the ordered L12-Fe3Pt, L10-FePt and L12-FePt3 phases, especially at low temperatures, have been well determined, and the related invariant reactions have been evaluated. Finally, a revised Fe–Pt phase diagram has been proposed.

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31

"L10 ordered phase formation in FePt, FePd, CoPt, and CoPd alloy thin films epitaxially grown on MgO(001) single-crystal substrates." Journal of Applied Physics 111, no. 7 (April 2012): 07A708. http://dx.doi.org/10.1063/1.3672856.

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