결정 구조가 FePt 산소 발생 반응 전기 화학적 촉매에 미치는 영향

정원석,강기재,김계엽,윤갑인,강기석,한승우 한국물리학회 2015 New Physics: Sae Mulli Vol.65 No.9

We investigated the overpotential of the oxygen evolution reaction for the FePt catalyst by using a density functional theory calculation. We conducted the calculation for two types of FePt catalysts: FePt with an ordered L10 crystal structure and FePt with atoms randomly distributed at the face-centered-cubic (FCC) crystal sites. First, we investigated the surface energy of the L10 FePt surface and concluded that the reacting surface was a (111) surface because of its low surface energy. Next, we calculated the free energy of the oxygen evolution reaction (OER) steps and obtained the theoretical overpotentials for the two types of FePt catalysts. The overpotentials for the ordered L10 and the disordered FCC FePt catalysts were found to be 2.26 V and 2.17 V, respectively. The disordered FCC FePt is expected to have a higher catalyst activity than the ordered L10 FePt. 제일원리 밀도범함수이론 계산을 통해 정렬된 L10 결정구조의 FePt와 FCC 구조에서 원자가 무작위로 배치되어 있는 FePt 촉매의 산소 발생 반응 과전압을 알아보았다. 다양한 표면 방위에 대한 에너지 계산 결과, L10 FePt의 (111)면이 가장 안정하여 반응에 가장 크게 관여하는 표면임을 알 수 있었다. 산소 발생 반응의 각 단계의 자유 에너지를 계산하여 각 촉매의 이론적 과전압을 계산한 결과, L10 결정구조의 FePt와 원자 배열이 무작위한 FCC FePt의 과전압은 각각 2.26 V, 2.17 V로 원자 배열이 무작위한 FCC FePt의 과전압이 0.09 V 낮게 계산되었다. 이는 산소 발생 반응 촉매로서 널리 쓰이는 Pt의 과전압인 2.55 V 보다 낮은 값이다.

Block Copolymer Directed One-Pot Simple Synthesisof L1₀-Phase FePt Nanoparticles inside Ordered MesoporousAluminosilicate/Carbon Composites

Kang, Eunae,Jung, Hyunok,Park, Je-Geun,Kwon, Seungchul,Shim, Jongmin,Sai, Hiroaki,Wiesner, Ulich,Kim, Jin Kon,Lee, Jinwoo American Chemical Society 2011 ACS NANO Vol.5 No.2

<P>A 'one-pot' synthetic method was developed to produce L1(0)-phase FePt nanopartides in ordered mesostructured aluminosilicate/carbon composites using polyisoprene-block-poly(ethylene oxide) (Pl-b-PEO) as a structure-directing agent. Pl-b-PEO block copolymers with aluminosilicate sols are self-assembled with a hydrophobic iron precursor (dimethylaminomethylferrocene) and a hydrophobic platinum precursor (dimethyl(1,5-cyclooctadiene)platinum(II)) to obtain mesostructured composites. The as-synthesized material was heat-treated to 800 degrees C under an Ar/H-2 mixture (5% v/v), resulting in the formation of fct FePt nanocrystals encapsulated in ordered mesopores. By changing the quantities of the Fe and Pt precursors in the composite materials, the average particle size of the resulting fct FePt, estimated using the Debye-Scherer equation with X-ray diffraction patterns, can be easily controlled to be 2.6-10.4 nm. Using this simple synthetic method, we can extend the size of directly synthesized fct FePt up to similar to 10 nm, which cannot be achieved directly in the colloidal synthetic method. All fct FePt nanoparticles show hysteresis behavior at room temperature, which indicates that ferromagnetic particles are obtained inside mesostructued channels. Well-isolated, similar to 10 nm fct FePt have a coercivity of 1100 Oe at 300 K. This coercivity value is higher than values of fct FePt nanoparticles synthesized through the tedious hard template method by employing SBA-15 as a host material. The coercivity value for FePt-1 (2.6 nm) at 5 K is as high as 11 900 Oe, which is one of the largest values reported for FePt nanoparticles, or any other magnetic nanoparticles. The fct FePt nanoparticles also showed exchange-bias behavior.</P>

FePt-Al-O 후막의 자기특성

장평우 청주대학교 산업과학연구소 2007 産業科學硏究 Vol.24 No.2

Coercively of FePt binary alloy films manufactured in an rf magnetron equipment was reported to decrease with film thickness. To improve the low coercively of FePt thick films FePt-Al-O films were sputtered from fePt-Al_(2)O_(3) compiles target for which several Al_(2)O_(3) chips were placed on the Feet alloy target. As a result a coercively larger than 7 kOe could be obtained in FePt-Al-O films with Al contents less than 0.5 at. %.

Synthesis and characterization of FePt nanoparticle/ multi walled carbon nanotube composites

Yan Wang,Lian Gao,Jing Sun,Yangqiao Liu 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.1

This paper reports the synthesis of FePt nanoparticle (NPs)/multi walled carbon nanotube (FePt/MWNTs) nanocomposites,which have important potential implications to orient CNTs and the development of catalysts. FePt NPs have been synthesized by a chemical method, whose crystallite size is about 2.5-4 nm with a Fe content ranging from 50 to 65. MWNTs produced by chemical vapor deposition have been decorated with FePt nanoparticles under mild conditions without any pretreatment. When the diameter of MWNTs is about 20-30 nm, FePt NPs mostly attach onto the sidewalls of MWNTs. The amount of FePt NPs attached onto the MWNTs can be well controlled. Transmission electron microscope (TEM), high-resolution transmission electron micrograph (HRTEM) studies, and energy dispersive X-ray spectroscopy (EDS) spectra were performed to observe the nanostructure of these nanocomposites. The orientation in these nanocomposites has been studied initially.

The Effect of Cr Dosage on FePt Nanoparticle Formation

C. Won,D. J. Keavney,R. Divan,S. D. Bader 한국자기학회 2006 Journal of Magnetics Vol.11 No.4

The search for high-density recording materials has been one of most active and vigorous field in the field of magnetism. FePt-L1? nanoparticle has emerged as a potential candidate because of its high anisotropy. In this paper, we provide an overview of recent work at Argonne National Laboratory that contributes to the ongoing dialogue concerning the relation between structure and properties of the FePt nanoparticle system. In particular we discuss the ability to control structure and properties via dosing with Cr. Cr-dosed FePt films were grown via molecular beam epitaxy and annealed at 550℃ in an ultrahigh vacuum chamber, and were studied with the surface magneto-optic Kerr effect (SMOKE), scanning electron microscopy (SEM) and x-ray magnetic circular dichroism (XMCD). We found that small dosage of Cr helps to generate L1? phase FePt magnetic nanoparticles with small size, defined shape and regular spatial distribution on MgO (001) substrate. The nanostructures are ferromagnetic with high magnetic coercivity (~0.9T) and magnetic easy axis in the desired out-of-plane orientation. We also show that controlling the lateral region where nanostructures exist is possible via artificial patterning with Cr.

Effects of Annealing Pressures on the Ordering and Microstructures of FePt

Xiaohong Li,Zhaodi Feng,Yang Li,Wenpeng Song,Qian Zhang,Baoting Liu 한국자기학회 2013 Journal of Magnetics Vol.18 No.4

FePt:Ag (100 nm) nanocomposite thin films were prepared on naturally-oxidized Si substrates by dc magnetron sputtering at room temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to investigate the effects of annealing pressures on the ordering processes and microstructures of these films. The average sizes for the L10 ordered domains and the FePt grains are reduced to d = 9 nm and D = 13 nm from d = 19 nm and D = 34 nm, respectively, when the annealing pressure is enhanced to 0.6 GPa from room pressure at 873 K. Furthermore, the size distribution is improved into a narrow range. With increasing pressure, the coercivity of L10-FePt:Ag thin films decreases from 15.1 to 7.6 kOe. In the present study, the effects of high pressure on the L10 ordering processes and microstructures of FePt:Ag nanocomposite films were discussed.

PREVENTION OF SINTERING DURING ANNEALING PROCESS OF FePt NANOPARTICLES COATED WITH ZnO SHELL

HOSSEIN ZEYNALI,HOSSEIN AKBARI,S. ARUMUGAM,ZOHREH CHAMANZADEH,G. KALAISELVAN,REYHANEH KARIMI GHASABEH 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2012 NANO Vol.7 No.6

Monodispersed 4.1 nm FePt nanoparticles with narrow size distribution were successfully synthesized by the chemical polyol process with co-reduction of Fe(acac)3 and Pt(acac)2 in the presence of 1,2-hexadecanediol as a reducing agent. To achieve hard ferromagnetic behavior with L10 phase and face center tetragonal (fct) structure, high temperature annealing is performed. Annealing causes the surfactant surrounding particles to decompose and agglomeration of particles occurs. In the present work, chemically synthesized FePt nanoparticles were coated with nonmagnetic ZnO oxide shell to prevent them from sintering. Coercivity of FePt and FePt/ZnO nanoparticles increases from 5 kOe to 10 kOe and 1.8 kOe to 6 kOe respectively, with the increasing annealing temperatures from 650 to 750?C.

FePt/MgO(001) 자성박막 결정화의 두께의존성

정지욱,이민수,조태식,Jeung, Ji-Wook,Yi, Min-Soo,Cho, Tae-Sik 한국전기전자재료학회 2010 전기전자재료학회논문지 Vol.23 No.2

The crystallization of FePt/MgO(001) magnetic thin films of various thicknesses has been studied using synchrotron x-ray scattering, atomic force microscope, and vibrating sample magnetometer. In film with a 499-$\AA$-thick, face-centered tetragonal, ordered FePt phase was dominantly crystallized into perpendicular (001) grains keeping the magnetically easy c-axis normal to the film plane during annealing. In film with a 816-$\AA$-thick, however, longitudinal (110) grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular (001) grains. The behavior of the magnetic properties was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of the c-axis oriented perpendicular grains near the film/substrate interfacial area.

<Retraction> INVESTIGATION OF HIGH-COERCIVITY FePt-C NANOGRANULAR FILMS FOR PERPENDICULAR MAGNETIC RECORDING (PMR) MEDIA

JIEGANG PENG,S. XUE,Z. YAN,X. WU,L. ZHAN 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2011 NANO Vol.6 No.6

In this work, we studied FePt-C nanogranular films were fabricated for ultrahigh density perpendicular recording media towards 1 Tbits/in^2. For the optimized growth conditions, we achieved a Fe_(52)Pt_(48)-C50% granular film with uniform grain size of 6.4 ± 1.5 nm, shown in the TEM image. It also has an excellent MH loop shape with a perpendicular coercivity of 20 kOe, and squareness of 1.We studied the thermal stability of the optimized film and obtained the energy barrier Eb of 340 k_BT at room temperature, meaning that excellent thermal stability as magnetic recording media.

Amorphous Cr-Ti Texture-inducing Layer Underlying (002) Textured bcc-Cr alloy Seed Layer for FePt-C Based Heat-assisted Magnetic Recording Media

Seong-Jae Jeon,Shintaro Hinata,Shin Saito 한국자기학회 2016 Journal of Magnetics Vol.21 No.1

Cr100-xTix amorphous texture-inducing layers (TIL) were investigated to realize highly (002) oriented L1₀ FePt-C granular films through hetero-epitaxial growth on the (002) textured bcc-Cr80Mn20 seed layer (bcc-SL). Asdeposited TILs showed the amorphous phase in Ti content of 30 ≤ x (at%) ≤ 75. Particularly, films with 40 ≤ x ≤ 60 kept the amorphous phase against the heat treatment over 600 ℃. It was found that preference of the crystallographic texture for bcc-SLs is directly affected by the structural phase of TILs. (002) crystallographic texture was realized in bcc-SLs deposited on the amorphous TILs (40 ≤ x ≤ 70), whereas (110) texture was formed in bcc-SLs overlying on crystalline TILs (x < 30 and x > 70). Correlation between the angular distribution of (002) crystal orientation of bcc-SL evaluated by full width at half maximum of (002) diffraction (FWHM) and a grain diameter of bcc-SL indicated that while the development of the lateral growth for bcc-SL grain reduces FWHM, crystallization of amorphous TILs hinders FWHM. L1₀ FePt-C granular films were fabricated under the substrate heating process over 600 ℃ with having different FWHM of bcc-SL. Hysteresis loops showed that squareness (Mr/Ms) of the films increased from 0.87 to 0.95 when FWHM of bcc-SL decreased from 13.7 ˚ to 3.8 ˚. It is suggested that the reduction of (002) FWHM affects to the overlying MgO film as well as FePt-C granular film by means of the hetero-epitaxial growth.