Microstructures and magnetic anisotropy of single-layered Fe-Pt alloy films by in-situ annealing

The single-layered Fe-Pt films with thickness of 30 nm are in-situ deposited directly on Si substrate at various substrate temperatures (Ts) of 350 to 590 degrees C. As the Fe-Pt film is sputtered at substrate temperature is 350 degrees C, it shows (111) preferred orientation and tends to in-plane magnetic anisotropy. The L1(0) Fe-Pt film with (001) texture is obtained and exhibited perpendicular magnetic anisotropy as the substrate temperature is increased to 470 degrees C. The perpendicular coercivity (Hc perpendicular), saturation magnetization (Ms) and perpendicular squareness (S perpendicular) of this film are 6.9 kOe, 674 emu/cm3 and 0.89, respectively, which reveal its significant potential as perpendicular magnetic recording media.     

Low-rate sputter-deposited Fe3Si thin films on Si substrates: structural and ferromagnetic properties

Fe3Si thin films were sputter-deposited on Si(001) substrates. Structural investigations show that Fe3Si was deposited poly-crystalline with a Si-containing layer at the Fe3Si/Si interface. The formation of the layer was attributed to the influence of low deposition rates used in this study on the grain nucleation in Fe3Si. This layer helps to stabilize the ferromagnetic properties of the subsequent annealed films at 350 degrees C with 5 Oe obtained for coercive field H(c), approximately 920 emu/cm3 for saturation magnetization M(s) and approximately 0.9M(s) for remnant magnetization M(r).     

Structural and Magnetic Properties of Sm_3(Fe,Ti)_(29) and Sm_3(Fe,Ti)_(29)X_y (X=H, N) Compounds

1. IntroductionRecelltly new intermetallic compounds NdZ(Fe,Ti)lo and RZ(Feo.91Vo.og)19 (R=Y, Nd, Sin, Gd) werediscovered by Collocott et al.II] and Shcherbakovaat al.IZ], respectively. The crystal structure of thesenew phases has been identified to be Nd3(Fe, Ti)29type structure using X-ray diffraction by Li et al.I3].Among them, the Sin3(Fe,Ti)29N. compound exhibitsstrong uniaxial anisotropy' and its saturation magnetization is very close to that of S.,Fe,,N;'] compound.The hydr…     

Rapid synthesis and characterization of maghemite nanoparticles

Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe203-SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.     

Magnetic and catalytic properties of Cu0.5Zn0.5Fe2O4 nanocrystallite powders

Cu0.5Zn0.5Fe2O4 nanocrystallite powders (average size 13 nm) were synthesized from Cu-Zn spent catalyst (fertilizers) industries and ferrous sulfate wastes formed during iron and steel making. Cu-Zn catalyst (22.4% Cu and 26.4% Zn) was chemically treated with sulfuric acid at temperature 80 degrees C for 1 hr for the complete dissolving of copper and zinc into sulfate solution, then the produced solution was mixed with stoichiometric ratio of ferrous sulfate and the mixture was chemically precipitated as hydroxides followed by hydrothermal processing. The parameters affecting the magnetic properties and crystallite size of the produced ferrites powder e.g., temperature, time, and pH were systemically studied. X-ray diffraction analysis was used in order to determine the average crystallite size and phase identifications of the produced powder. The magnetic properties were studied by vibrating sample magnetometry. The results showed that the average crystallite size of the powder decreased for the ferrites powder formed at 150 degrees C and then increased by increasing the temperature to 200 degrees C. Interestingly, the saturation magnetization (Bs), remanent magnetization (Br) and coercive force (Hc) were 25.03 emu/g, 0.71 emu/g, and 4.83 Oe, respectively at hydrothermal temperature 150 degrees C for 24 hr and changed to 16.38 emu/g, 0.3864 emu/g, and 5.2 Oe at 150 degrees C and 72 hr. The produced nanoferrite powders are used for studying the catalytic activity of CO conversion to CO2 at different temperatures, pH and times. The maximum conversion (82%) is obtained at temperature 150 degrees C for 24 hrs and pH 12.     

Microstructural enhancement of high coercivity L1(0)-FePt films for next-generation magnetic recording media

The effects of substrate Ar-ion milling and Ta adhesion layer on the microstructural and magnetic properties of L1(0)-FePt films prepared on Si, SiO2, and glass substrates were investigated. It was discovered that the relatively large in-plane surface roughness of CrRu/MgO/FePt films deposited on Si substrates was due to the deformation of the CrRu layer when the composition was heated to 550 degrees C. More than an order of magnitude improvement for the in-plane surface roughness was achieved when substrate Ar-ion milling or Ta adhesion layer was incorporated into the process. While the Ta adhesion layer proved to be detrimental to the (200) growth of the CrRu layer, optimal FePt film properties with coercivity values larger than 2 Tesla and out-of-plane roughness less than 1 nm were achieved when only substrate Ar-ion milling was implemented.     

过渡金属(Mn2+、Ni2+、Fe3+、Cu2+)掺杂ZnO基稀磁半导体的制备及性质

利用溶液腐蚀法制备了Mn2+、Ni2+、Fe3+、Cu2+离子掺杂的ZnO基稀磁半导体。XRD表明掺杂后的ZnO仍然保持单一的纤锌矿结构,没有任何杂质相产生。由紫外-可见光反射谱可知掺杂后吸收边发生了红移。掺杂前ZnO的带隙为3.20eV,对样品分别掺入Mn、Ni、Fe和Cu后的带隙分别为3.19eV、3.15eV、3.08eV和3.17eV。掺杂后样品的室温PL谱除了紫外发射峰外,对于Mn掺杂的样品还在蓝光区域出现了2个分别位于424nm和443nm的发射峰,Fe掺杂的样品出现了一个位于468nm的微弱发射峰,Cu掺杂的样品出现了位于469nm及535nm的很宽的发射峰。室温磁滞回线显示掺杂后样品有明显的铁磁性,掺入Mn、Ni、Fe和Cu样品的剩余磁化强度(Ms)分别为0.3902×10-3emu/cm3、0.454emu/cm3、0.372emu/cm3和0.962×10-3emu/cm3,矫顽力分别为47Oe、115.92Oe、99.33Oe和23Oe。经分析室温铁磁性来源于缺陷调制的Mn2+-Mn2+长程铁磁交换相互作用。     

Co-Fe metal/native-oxide multilayers: a new direction in soft magnetic thin film design II. Microscopic characteristics and interactions

Co/sub x/Fe/sub 100-x/ metal/native-oxide multilayer (MNOM) films exhibit soft magnetic properties, large magnetization, high resistivity, and a potential operating bandwidth of several gigahertz. These attractive characteristics are facilitated by ultrathin magnetic native oxide layers introduced to provide a high-resistivity barrier between nanocrystalline metal layers while preserving interlayer coupling and contributing to the net moment. This paper addresses several important features of the MNOM system from a microscopic perspective. The uniaxial anisotropy of MNOM thin films is discussed in detail and "exchange averaging" is invoked to account for its vanishingly small effective dispersion. The role of the native oxide in establishing interlayer exchange coupling is demonstrated, and a detailed account of the nature of the oxide is presented. In the Fe MNOM system, the oxide is shown to have a volume-averaged magnetization of 732(35) emu/cm/sup 3/, with a temperature dependence comparable to that of metallic Fe. The magnetism of this largely "interfacial" oxide is supported by the metal and collapses in the absence of the metal. The oxide retains a large net moment for Co fractions up to at least x=50, but oxide magnetism is lost at high Co fractions, coinciding with the loss of soft magnetic properties.     

Removal of organic carbon from wastepaper pulp effluent by lab-scale solar photo-Fenton process

The bleaching wastewater effluent from a pulp and paper mill (located in Tianjin, China) was treated with solar photo-Fenton process in a lab-scale reactor (22 cm x 15 cm thermostatic dish). The mill used wastepaper as raw material and the effluent contained 332 mgL(-1) of total organic carbon (TOC) and 1286 mg L(-1) of COD. The treatment involved a constant intensity of irradiation (0.2 kW/m(2)) with a solar simulator of 250 W xenon lamp and various conditions of pH, temperature, and initial concentrations of H(2)O(2) and Fe(II). The better treatment conditions were searched for in the ranges of initial Fe(II) concentration from 31 to 310 mgL(-1) (initial pH 3.0, 30 degrees C), initial H(2)O(2) concentration from 0.5 to 3 Dth (1 Dth=1883 mg L(-1) for TOC mineralization) (initial pH 3.0, 30 degrees C), initial pH from 2.0 to 6.0 (1 and 2 Dth, 10:1 of H(2)O(2)/Fe(II), 30 degrees C), and temperature from 30 to 50 degrees C (1 Dth, 10:1 of H(2)O(2)/Fe(II), initial pH 2.8). TOC removal generally showed the initial fast increase stage within the first sampling time of 15 min, followed by the gradual increase stage in the remaining sampling time of 180 min experimental time course. The highest percentage of TOC removal in the first stage was about 60% when the initial pH was either 2.8 (H(2)O(2)=1 Dth, ratio=10:1, temperature=30-50 degrees C) or 3.5 (H(2)O(2)=2 Dth, ratio=10:1, temperature=30 degrees C). Also under the latter condition, the value reached 82% at 120 min and was projected to reach 94% at 180 min. According to the positive effect of temperature increase on TOC removal observed in this experiment, further increase above these maximum values is possible if the temperature of the above condition were increased from 30 to 40 degrees C or 50 degrees C. Furthermore, under most of the treatment conditions, the TOC removal reached or was projected to reach over 60% toward the end of the experiments. The result indicated that the solar photo-Fenton process has a potential to effectively remove TOC from the wastepaper pulp effluent on a large scale.     

Room temperature ferromagnetism in Co-incorporated TiO2 thin films

Observation of room temperature ferromagnetism (RTFM) in nano-crystalline Co-incorporated titanium dioxide [Ti(1-x)Co(x)O2(x = 0.05)] thin films prepared by spray pyrolysis technique is reported. While only the anatase phase was detected in as-deposited 5 at.% Co-incorporated TiO2 film, a small amount of rutile phase developed following its vacuum annealing. Besides, no X-ray diffraction peak corresponding to cobalt metal could be detected in any of the two films. SQUID magnetometry of both pristine and Co-doped thin films at room temperature elucidated distinct ferromagnetic behavior in 5 at.% Co-incorporated as-deposited film with saturation moment M(s) approximately 5.6 emu/cm3 which got enhanced up to 11.8 emu/cm3 on subsequent vacuum annealing. From the zero field cooled magnetization measurement we confirmed the absence of Co-metal clusters. The electrical resistivity was found to be greater than 108 omega-cm for the films. Based on the magnetic and electrical measurements the origin of RTFM has been attributed to the bound magnetic polaron (BMP) model.     

Effect of MoO3 on the synthesis of boron nitride nanotubes over Fe and Ni catalysts

Synthesis of boron nitride nanotubes at reduced temperature is important for industrial manufactures. In this study boron nitride nanotubes were synthesized by thermal evaporation method using B/Fe2O3/MoO3 and B/Ni2O3/MoO3 mixtures separately with ammonia as the nitrogen source. The growth of boron nitride nanotubes occurred at 1100 degrees C, which was relatively lower than other metal oxides assisted growth processes requiring higher than 1200 degrees C. MoO3 promoted formation of B2O2 and aided boron nitride nanotubes growth at a reduced temperature. The boron nitride nanotubes with bamboo shaped, nested cone structured and straight tubes like forms were evident from the high resolution transmission electron microscopy. Metallic Fe and Ni, formed during the process, were the catalysts for the growth of boron nitride nanotubes. Their formation was established by X-ray diffraction. FT Raman showed a peak due to B-N vibration of BNNTs close to 1370 cm(-1). Hence MoO3 assisted growth of boron nitride nanotubes is advantageous, as it significantly reduced the synthesis temperature.     

Synthesis of high magnetic moment CoFe nanoparticles via interfacial diffusion in core/shell structured Co/Fe nanoparticles

We report the synthesis of high magnetic moment CoFe nanoparticles via the diffusion of Co and Fe in core/shell structured Co/Fe nanoparticles. In an organic solution, Co nanoparticles were coated with a layer of Fe to form a Co/Fe core/shell structure. Further raising the solution temperature led to inter-diffusion of Co and Fe and formation of CoFe alloy nanoparticles. These nanoparticles have high saturation magnetization of up to 192 emu/g CoFe and can be further stabilized by thermal annealing at 600 °C. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. These two authors made an equal contribution to the work.     

Low temperature synthesis of magnetite and maghemite nanoparticles

We report on the synthesis of iron oxide nanoparticles below 100 degrees C by a simple chemical protocol. The uniqueness of the method lies in the use of Ferrous ammonium sulphate (in conjugation with FeCl3) which helps maintain the stability of Fe2+ state in the reaction sequence thereby controlling the phase formation. Hexamine was added as the stabilizer. The nanoparticles synthesized at three different temperatures viz, 5 degrees, 27 degrees, and 95 degrees C are characterized by several techniques. Generally, when a mixture of Fe3+ and Fe2+ is added to sodium hydroxide, alpha-Fe2O3 (the anti-ferromagnetic phase) is formed after the dehydration process of the hydroxide. In our case however, the phases formed at all the three temperatures were found to be ferro (ferri) magnetic, implying modification of the formation chemistry due to the specifics of our method. The nanoparticles synthesized at the lowest temperature exhibit magnetite phase, while increase in growth temperature to 95 degrees C leads to the maghemite phase.     

Temperature-programmed GC using silicon microfabricated columns with integrated heaters and temperature sensors

Columns were fabricated in silicon substrates by deep reactive-ion etching. The channels were sealed with a glass wafer anodically bonded to the silicon surface. Heaters and temperature sensors were fabricated on the back side of each column chip. A microcontroller-based temperature controller was used with a PC for temperature programming. Temperature programming, with channel lengths of 3.0 and 0.25 m, is described. The 3.0-m-long channel was fabricated on a 3.2 cmx3.2 cm chip. Four columns were fabricated on a standard 4-in. silicon wafer. The 0.25-m-long channel was fabricated on a 1.1 cmx1.1 cm chip, and approximately 40 columns could be fabricated on a 4-in. wafer. All columns were coated with a nonpolar poly(dimethylsiloxanes) stationary phase. A static coating procedure was employed. The 3.0-m-long column generated about 12000 theoretical plates, and the 0.25-m-long channel generated about 1000 plates at optimal carrier gas velocity. Linear temperature ramps as high as 1000 degrees C/min when temperature programmed from 30 to 200 degrees C were obtained with the shorter column. With the 0.25-m-long column, normal alkanes from n-C5 through n-C15 were eluted in less than 12 s using a temperature ramp rate of 1000 degrees C/min. Temperature uniformity over the column chip surface was measured with infrared imaging. A variation of about 2 degrees C was obtained for the 3.0-m-long channel. Retention time reproducibility with temperature programming typically ranged from +/-0.15% to +/-1.5%. Design of the columns and the temperature controller are discussed. Performance data are presented for the different columns lengths.     

Influence of column temperature on the electrophoretic behavior of myoglobin and alpha-lactalbumin in high-performance capillary electrophoresis

The influence of column temperature on the electrophoretic behavior of myoglobin and alpha-lactalbumin in high-performance capillary electrophoresis (HPCE) is presented. The major effect of temperature is to shorten the analysis time by decreasing the viscosity, but specific temperature effects on the protein migration behavior were also observed. Myoglobin, under high field (350 V/cm), was essentially temperature stable from 20 to 45 degrees C, but at constant current, a second form of myoglobin could be detected at both 214 and 410 nm. The initial form appeared to correspond to the Fe3+ and the second to the Fe2+ oxidation state of the heme iron. The rate of conversion from Fe3+ to the reduced Fe2+ in myoglobin, under given electrophoretic conditions, followed first-order kinetics with a rate constant at 30 degrees C of 304 s-1. A second protein, alpha-lactalbumin type III, demonstrated a conformational transition that resulted in asymmetric peaks and sigmodial mobility plots versus temperature in the transition region.     

Magnetic and hydrogel composite materials for hyperthermia applications

Micron-sized magnetic particles (Fe3O4) were dispersed in a polyvinyl alcohol hydrogel to study their potential for hyperthermia applications. Heating characteristics of this ferrogel in an alternating magnetic field (375 kHz) were investigated. The results indicate that the amount of heat generated depends on the Fe3O4 content and magnetic field amplitude. A stable maximum temperature ranging from 43 to 47 degrees C was successfully achieved within 5-6 min. The maximum temperature was a function of Fe3O4 concentration. A specific absorption rate of up to 8.7 W/g Fe3O4 was achieved; this value was found to depend on the magnetic field strength. Hysteresis loss is the main contribution to the heating effect experienced by the sample.     

纳米Fe3O4/聚苯胺复合粒子的制备及其在交变磁场下的发热性能

用水解沉淀法合成了纳米Fe₃O₄粒子,并在其悬浮液中原位包覆聚苯胺,制备出纳米Fe₃O₄/聚苯胺复合粒子。研究了两种纳米粒子在交变磁场下的发热性能,对它们在定向集热治疗肿瘤中的应用前景进行了评价。纳米Fe₃O₄粒子的粒径为10~30nm,表面包覆聚苯胺后,复合粒子的粒径为30~50nm。纳米Fe₃O₄粒子的比饱和磁化强度为50.05Am2/kg,矫顽力为10.9kA/m;纳米Fe₃O₄/聚苯胺复合粒子的比饱和磁化强度为26.34Am2/kg,矫顽力为0。在10mg/mL的生理盐水悬浮液中,在外加交变磁场作用30min后,纳米Fe₃O₄粒子悬浮液的温度为63.6℃,纳米Fe₃O₄/聚苯胺悬浮液的温度为52.4℃,二者均达到了医学上定向集热治疗肿瘤用热籽的发热要求,是很有应用前景的医用纳米材料。      

Effect of Annealing Conditions in Hydrogen Atmosphere on Structural,Optical and Magnetic Properties of Nanocrystalline CdO Codoped with Cu and Co Ions for DMS Applications

Cadmium oxide powder codoped with Cu and Co ions (Cd_0.94Cu_0.01Co_0.05O) was synthesised by thermal co-decomposition of a mixture of cadmium acetate dihydrate, bis(acetylacetonato)copper(II) and bis(acetylacetonato)cobalt(II) complexes. The purpose of the present investigation is to study the effect of H₂-annealing conditions on the evolution of structure, optical and magnetic properties by varying temperature (300, 350 and 400 °C) and duration time (30 and 60 min). X-ray fluorescence (XRF) and X-ray diffraction (XRD) methods confirm the purity and the formation of single nanocrystalline phase of the as-prepared powder; thus, both Cu and Co ions were incorporated into CdO lattice, forming solid solutions. Magnetic measurements reveal that the as-prepared solid solution (SS) gained paramagnetic (PM) properties, although pure CdO itself is considered as diamagnetic (DM). The measured effective magnetic moment of doped Co²⁺ was 3.55 μ _B. Interestingly, it was found that the hydrogenation process could transform the properties of the SS into room-temperature ferromagnetic (RT-FM) only. For example, the coercivity (H _c), remanence (M _r) and saturation magnetisation (M _s) were 279 Oe, 0.187 emu/g and 1.739 emu/g, respectively for SS annealed in H₂ gas at 350 °C for 30 min. Thus, the possibility of producing CdO with RT-FM was proved, where the magnetic characteristics were tailored by doping and post treatment under H₂ gas, thereby a new potential candidate to be used as a dilute magnetic semiconductor (DMS). However, the real effect of H₂ annealing on such drastic transformation in the magnetic behaviour needs some in-depth theoretical research work.     

Dependence of ferroelectric and magnetic properties on measuring temperatures for polycrystalline BiFeO(3) films

A multiferroic BiFeO(3) film was fabricated on a Pt/Ti/SiO(3)/Si(100) substrate by a chemical solution deposition (CSD) method, and this was followed by postdeposition annealing at 923 K for 10 min in air. X-ray diffraction analysis indicated the formation of the polycrystalline single phase of the BiFeO(3) film. A high remanent polarization of 89 microC/cm(2) was observed at 90 K together with a relatively low electric coercive field of 0.32 MV/cm, although the ferroelectric hysteresis loops could not be observed at room temperature due to a high leakage current density. The temperature dependence of the ferroelectric hysteresis loops indicated that these hysteresis loops lose their shape above 165 K, and the nominal remanent polarization drastically increased due to the leakage current. Magnetic measurements indicated that the saturation magnetization was less than 1 emu/cm(3) at room temperature and increased to approximately 2 emu/cm(3) at 100 K, although the spontaneous magnetization could not appear. The magnetization curves of polycrystalline BiFeO3 film were nonlinear at both temperatures, which is different with BiFeO3 single crystal.