Nanoparticle composites: FePt with wide-band-gap semiconductor

We present a simple way to synthesize FePt and ZnO (wide-band-gap semiconductor) nanoparticle composites. The FePt nanoparticles were fabricated using the method reported by Sun et al. By controlling the heating rate, 3 nm FePt nanoparticles were synthesized. Well-dispersed FePt and ZnO nanoparticle composites were prepared by further adding zinc acetate and oleyl amine into the 3 nm FePt nanoparticle dispersion. By controlling the molar ratio of the FePt and zinc acetate, FePt and ZnO nanoparticle composites with different FePt particle fractions were obtained. The intensity of photo luminescence spectra of the nanoparticle composites increases very much with decreasing FePt particle fraction, whereas the peak position shifts a little. After annealing at 550 °C for half an hour, the nanoparticle composites become magnetically hard or semi-hard with coercivity much dependent on the FePt particle volume fraction. The coercivity of the composites increases with annealing temperature. The composites hold the promise of applications in new generation recording and/or optical devices.     

Very high coercivities of top-layer diffusion Au/FePt thin films

The Au/FePt samples were prepared by depositing a gold cap layer at room temperature onto a fully ordered FePt layer, followed by an annealing at 800 °C for the purpose of interlayer diffusion. After the deposition of the gold layer and the high-temperature annealing, the gold atoms do not dissolve into the FePt Ll₀ lattice. Compared with the continuous FePt film, the TEM photos of the bilayer Au(60 nm)/FePt(60 nm) show a granular structure with FePt particles embedded in Au matrix. The coercivity of Au(60 nm)/FePt(60 nm) sample is 23.5 kOe, which is 85% larger than that of the FePt film without Au top layer. The enhancement in coercivity can be attributed to the formation of isolated structure of FePt ordered phase.     

室温生长MgO底层诱导(001)取向FePt薄膜的有序化过程对FePt成分的依赖

室温下通过磁控溅射在表面热氧化的Si基片上生长了MgO/Fe_xPt_100-x双层膜和Fe_xPt_100-x单层膜系列样品，Fe_xPt_100-x的原子成分x=48—68.研究了热处理前后不同成分FePt薄膜的晶体结构和磁性的变化，尤其是MgO底层的引入对FePt的晶体结构和磁性的影响 关键词： FePt(001)薄膜 0相')" href="#">L1₀相     

Strongly in-plane magnetized FePt thin film on ultrathin Fe underlayer

The effect of ultrathin Fe underlayer on the strong in-plane magnetization of FePt magnetic thin film was investigated. This FePt thin film could be attained using the ultrathin Fe underlayer with 1 nm thickness. The in-plane coercivity of FePt film with 20 nm thickness grown on ultrathin Fe underlayer was high up to 7400 Oe. However, its out-of-plane coercivity was extremely low to 350 Oe compared to those of FePt thin films in other conventional studies. This result indicates that FePt thin film was strongly in-plane magnetized by ultrathin Fe underlayer. The strong ordering phase transformation kinetics and the high texturing to in-plane direction of the FePt thin film by ultrathin Fe underlayer were confirmed by Kinetics Monte Carlo (KMC) simulation and XRD measurement result, respectively. It is also supposed that they are associated with the reduction of an interface free energy between the film and the substrate with an introduction of ultrathin underlayer.     

High coercivity FePt-C bulk magnet processed by spark plasma sintering and hot deformation

A high coercivity of 11 kOe has been obtained in spark plasma sintered and hot-deformed Fe₅₃Pt₄₄C₃ bulk magnets. The origin for the high coercivity has been investigated using X-ray diffraction and transmission electron microscopy. The average grain size of the ordered phase was ∼100 nm, which is less than the single domain size of the L1₀-FePt phase. Fe₃C particles were found surrounding the L1₀-FePt grains, which suppress the grain growth. The L1₀ ordering is also found to increase in hot-deformed sample by annealing in a magnetic field of 10 T at 600 °C.     

CoPt(FePt)-C纳米复合膜的结构与磁性

用磁过滤脉冲真空电弧沉积方法制备了CoPt(FePt) C纳米复合薄膜，并在不同温度下进行了退火处理，研究了薄膜中碳的含量以及退火温度对薄膜结构与磁性能的影响.制备态薄膜经过足够高的温度退火后，x射线衍射和磁力显微镜分析发现，在碳基质中生成了面心四方相的CoPt(FePt)纳米颗粒.对于特定组分为Co24Pt31C45和Fe43Pt35C22的薄膜，矫顽力以及颗粒尺寸都随退火温度的升高而增大，当退火温度为700℃时，Co24Pt31C45薄膜的矫顽力为21×105A/m，晶粒尺寸为17nm;当退火温度为650℃时，Fe43Pt35C22相应值分别为28×105A/m和105nm. 关键词： 磁记录材料 磁性薄膜 CoPt FePt纳米复合薄膜     

Effects of target-substrate geometry and ambient gas pressure on FePt nanoparticles synthesized by pulsed laser deposition

FePt nanoparticles, in the forms of nanoparticle agglomerates and floccules-like nanoparticle networks, can be synthesized by pulsed laser deposition (PLD) at different ambient gas pressures. Backward plume deposition (BPD), as special target-substrate geometry, can achieve higher uniformity in terms of agglomerate size and size distribution, compared to conventional PLD. Both as-deposited FePt nanoparticles exhibit low K_u fcc phase and post-annealing at 600 °C is required for the phase transition to high K_u fct phase. FePt nanoparticle agglomerates deposited by BPD were found to have better fct phase crystallinity after annealing, which may be caused by the higher kinetic energy of backward moving ablated species due to shorter travel distance.     

Langmuir-Blodgett self-assembly and electrochemical catalytic property of FePt magnetic nano-monolayer

Dispersed-well FePt nanoparticles with particle size ~5 nm have been prepared by hydrazine hydrate reduction of H₂PtCl₆·6H₂O and FeCl₂·4H₂O in ethanol–water system. By employing as-synthesized FePt nanoparticles, the monolayer can be formed by LB Technique. The structural, magnetic properties and electrochemical properties of FePt monolayer were respectively studied by XRD, TEM, VSM and CHI 820 electrochemical workstation. The as-synthesized particle has a chemically disordered fcc structure and can be transformed into chemically ordered fct structure after annealing treatment above 400°C. The coercivity of ordered fct FePt phase can be up to 2515Oe. CVs of 0.5 M H₂SO₄/0.5M CH₃OH on GCE modified with FePt nanoparticles monolayer films illustrate that the as-synthesized FePt is a kind of active electrochemical catalyst.     

Structural and magnetic properties of RF sputtered FePt/Fe multilayers

Series of [FePt(4min)/Fe(t_Fe)]₁₀ multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]_n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]_n multilayers decrease with Fe layer deposition time, and the energy product (BH)_max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase.     

缓冲层Ta对FePt薄膜L10有序相转变及矫顽力的影响

制备了Ta/FePt/C系列多层膜，研究了样品在不同温度退火后的磁特性和微结构.实验结果表明，不同厚度的Ta缓冲层具有不同的微结构特征，显著影响FePt层的L1₀有序相的形成及相应的矫顽力.当Ta缓冲层较薄，Ta层为非晶态，且较为粗糙，由此使FePt在界面处产生较多的缺陷并导致较高密度的晶界，在退火过程中，受束缚相对较弱的非晶态的Ta原子比较容易沿FePt的缺陷和晶界处向FePt层扩散，使FePt在相变过程中产生的应力比较容易释放，同时，Ta在扩散过程中产生的缺陷，降低了FePt有序 关键词： FePt薄膜 0相')" href="#">L1₀相 原子扩散