Fe3O4纳米粒子的制备与超顺磁性

采用红外光谱、X射线衍射、透射电子显微镜和振动样品磁强计对用化学共沉淀法制备出的纳米Fe3O4粒子进行了形貌、结构及磁性能表征.其中,红外和XRD测试结果表明制备出的Fe3O4粒子的物态和晶相结构;透射电子显微镜照片表明制备出的纳米四氧化三铁成球性好,且大部分四氧化三铁粒子的粒径在10nm左右;磁化曲线表明制备出的Fe3O4粒子无剩磁和矫顽力,具有超顺磁性.并且,将制备出的纳米Fe3O4粒子和块状Fe3O4的磁性能进行对比,探讨了Fe3O4由块状的亚铁磁性向纳米级的超顺磁性转变的原因.     

热处理工艺对尖晶石型Ni0.5Zn0.45Co0.05Fe2O4静磁性能的影响

利用溶胶凝胶法制备了尖晶石型 Ni0.5Zn0.45Co0.05Fe2O4 纳米颗粒,设置了3种热处理工艺,发现随着热处理温度的提高,热处理时间的延长,颗粒长大,静磁性能提高。当热处理温度为800℃,保温8h,材料具有比较好的静磁性能（Ms=30.241Oe,Hc=73.261 emg/g,μi=0.210）。另外,将前驱体在磁场条件下热处理,得到颗粒尺寸比同种热处理工艺未加磁场条件下的大,并且静磁性能有了比较大的提高,其比饱和磁化强度甚至比在更高热处理温度,更长热处理时间下制备的NiZnCo铁氧体大。     

High coercivity and high saturation magnetization Mn-Al thin films

Mn-Al thin films with the composition of 31-68 at.% Mn were prepared by rf magnetron sputtering at various substrate temperatures then annealed in vacuum. Effects of the chemical composition, substrate temperature and annealing temperature on the magnetic properties of Mn-Al films have been investigated. The analysis of X-ray diffraction and magnetic measurement indicate that τ-phase was synthesized at a composition range of 40-60 at.% Mn. However, the formation of large amount of τ-phase occurred for Mn₅₀-Al₅₀ films, which have a high coercivity up to about 3000 Oe and a fairly large saturation magnetization of about 420 emu/cc     

Influence of grain boundaries and voids on the saturated magnetization in Fe/sub 3/O/sub 4/ films at a low magnetic field

We report the magnetic behaviors of Fe/sub 3/O/sub 4/ thin films grown by zero field growth (ZFG) and field growth (FG) techniques during the sputtering process. In FG conditions, an in situ 300 Oe field during growth is applied to a substrate, inducing an easy axis of magnetization. Structural observations obtained by high-resolution transmission electron microscopy measurements clearly depicted a significant reduction of the grain boundaries and voids in the Fe/sub 3/O/sub 4/ films grown under FG conditions, thus explaining the saturated magnetization of the Fe/sub 3/O/sub 4/ films at about 0.01 T. This behavior was expected due to a remarkable reduction of the antiferromagnetic exchange couplings between grains for FG conditions. In addition, the zero-field-cooled magnetization of the ZFG samples showed an abrupt change at about 285 K, confirming the existence of defects or other phases in the ZFG films.     

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).     

磁场诱导和晶种联合法制备链状Fe_3O_4

以粒径为700nm的球形Fe3O4为晶种,将晶种加入到含有FeSO4.7H2O、FeCl3.6H2O与尿素的混合溶液中,在磁场诱导下制备链状Fe3O4。研究了磁场强度、晶种添加量、分散剂聚乙烯吡咯烷酮(PVP)质量浓度以及反应时间对产品形貌的影响。研究结果表明,随着磁场强度的增大、晶种量的增加,链状粒子数目显著增多;适量的PVP能使链状粒子分散平行排列。合成链状Fe3O4粒子的最佳工艺条件为磁场强度0.35T,晶种用量10%,PVP质量浓度7.5g/L,反应18h。磁性能测试表明,该链状Fe3O4粒子具有亚铁磁性,磁饱和强度为72.3emu/g,矫顽力为381Oe。     

Correlation study between structural, magnetic and transport properties of annealed Co thin films

This paper presents structural, magnetization and transport properties measurements carried out on as-deposited Co (400 Å) thin film as well as samples annealed in the temperature range 100-500 °C in steps of 100 °C for 1 h. The samples used in this work were deposited on float glass substrates using ion beam sputtering technique. The magnetization measurements carried out using MOKE technique, clearly indicates that as-deposited as well as annealed samples up to 500 °C show well saturation magnetization with applied magnetic field. The as-deposited sample shows coercivity value (H_c) of 26 Oe, and it is increased to 94 Oe for 500 °C-annealed sample. A minimum coercivity value of 15 Oe is obtained for 200 °C annealed sample. The XRD measurements of as deposited films show microcrystalline nature of Co film, which becomes crystalline with increase in annealing temperature. The corresponding resistivity measurements show gradual decrease in resistivity. AFM technique was employed to study the surface morphology of as deposited film as well as annealed thin films. Observed magnetization, and resistivity behaviour is mainly attributed to the (i) change in crystal structure (ii) increase in grain size and (iii) stress relaxation due to the annealing treatment.     

Preparation of cobalt-zinc ferrite (Co0.8Zn0.2Fe2O4) nanopowder via combustion method and investigation of its magnetic properties

Cobalt-zinc ferrite (Co_0.8Zn_0.2Fe₂O₄) was prepared by combustion method, using cobalt, zinc and iron nitrates. The crystallinity of the as-burnt powder was developed by annealing at 700 °C. Crystalline phase was investigated by XRD. Using Williamson-Hall method, the average crystallite sizes for nanoparticles were determined to be about 27 nm before and 37 nm after annealing, and residual stresses for annealed particles were omitted. The morphology of the annealed sample was investigated by TEM and the mean particle size was determined to be about 30 nm. The final stoichiometry of the sample after annealing showed good agreement with the initial stoichiometry using atomic absorption spectrometry. Magnetic properties of the annealed sample such as saturation magnetization, remanence magnetization, and coercivity measured at room temperature were 70 emu/g, 14 emu/g, and 270 Oe, respectively. The Curie temperature of the sample was determined to be 350 °C using AC-susceptibility technique.     

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。      

Preparation of Fe3O4 Film by in-situ Oxidative Hydrolysis on Chitosan

The Fe3O4 films were prepared by in-situ oxidative hydrolysis on chitosan. The structures and characteristics of the prepared Fe3O4 films were investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, atom force microscopy （AFM）, vibrating sample magnetometry （VSM） and thermogravimetric-differentia thermal analysis （TG-DTA）. The results show that, （1） the as-synthesized Fe3O4 films are pure Fe3O4 with cubic inverse spinel structure; （2） the network structured film can be obtained at lower temperature, and the compact particle film at higher temperature; （3） the prepared Fe3O4 films are super-paramagnetic, and the saturation magnetization is improved with increasing the reaction temperature, which is 49.03 emu/g at 80℃; （4） the temperature of phase transformation from Fe3O4 to a-Fe2O3 is about 495℃. Besides, the formation mechanism of Fe3O4 film was also proposed.     

Tuning exchange bias in core/shell FeO/Fe3O4 nanoparticles

Monodisperse 35 nm FeO nanoparticles (NPs) were synthesized and oxidized in a dry air atmosphere into core/shell FeO/Fe(3)O(4) NPs with both FeO core and Fe(3)O(4) shell dimensions controlled by reaction temperature and time. Temperature-dependent magnetic properties were studied on FeO/Fe(3)O(4) NPs obtained from the FeO NPs oxidized at 60 and 100 °C for 30 min. A large exchange bias (shift in the hysteresis loop) was observed in these core/shell NPs. The relative dimensions of the core and shell determine not only the coercivity and exchange field but also the dominant reversal mechanism of the ferrimagnetic Fe(3)O(4) component. This is the first time demonstration of tuning exchange bias and of controlling asymmetric magnetization reversal in FeO/Fe(3)O(4) NPs with antiferromagnetic core and ferrimagnetic shell.     

溅射法制备Mn-Zn铁氧体薄膜的磁性与微结构

以交替真空溅射的方法使用成分分别为MnFe2O4与ZnFe2O4的双靶制备了成分变化的系列Mn1-xZnxFe2O4铁氧体薄膜,衬底为Si(100)。薄膜的成分通过控制不同靶的溅射时间来进行调整。沉积态的薄膜呈非晶结构,在真空炉中以适当的温度对薄膜进行退火之后能够得到多晶Mn-Zn铁氧体薄膜。组成成分为Mn0.5Zn0.5Fe2O4的薄膜呈现了相对最高的饱和磁化强度。同时还研究了制备条件对薄膜结构与磁性的影响,如溅射氧分压,退火真空度,退火温度及薄膜厚度等等。制备的薄膜相对于块状材料具有较高的矫顽力,进而讨论了应力对薄膜矫顽力的影响。     

葡聚糖包覆纳米Fe3O4颗粒的研究

采用化学共沉淀法制备了葡聚糖包覆的纳米Fe3O4颗粒,平均粒径为6nm,包覆层厚度约为3～5nm,纳米Fe3O4粒径分布较窄.红外光谱分析可知,葡聚糖与纳米Fe3O4主要以氢键结合,结合Zeta电位和热重分析,分散作用主要是空间位阻作用,葡聚糖的包覆量约为10%.吸光度测试表明,随着葡聚糖用量的增加,悬浮液的稳定性提高.用量为25%时,悬浮液在室温下静止1周,无分层现象.包覆样的饱和磁化强度为60emu/g,具有良好的超顺磁性.     

油酸对微波水热法制备的纳米Fe_3O_4的影响

采用微波水热法制备纳米Fe3O4,并用油酸对其进行表面改性,获得油酸包覆的Fe3O4纳米粒子。利用XRD、FT-IR、TEM和振动样品磁强计对Fe3O4纳米粒子的结构、形貌、磁性能进行表征。结果表明:表面改性使得油酸分子中—COOH和Fe离子形成化学键;改性后的纳米Fe3O4粒子为粒度均匀的球形,具有良好的分散性,平均粒径约8nm;该产物具有超顺磁性,饱和磁化强度为61.8emu/g。     

Fe3O4/ 聚吡咯复合材料的制备及表征

以化学沉淀法制备Fe₃O₄ 纳米粒子, 采用乙醇对Fe₃O₄ 纳米粒子表面进行处理, 使其表面有机化, 然后通过乳液原位复合制备Fe₃O₄ / 聚吡咯复合材料。利用TEM, XPS, 四探针测试仪和震荡磁力计对其进行表征和检测。结果表明: 经醇处理的Fe₃O₄ 纳米粒子的分散性得到明显改善, Fe₃O₄ 纳米粒子被包覆在聚吡咯层内, 包覆层厚度为10 nm 左右, 复合材料具有优良的电性能和磁性能, 电导率e= 7. 69 s/ cm～13. 6 s/ cm, 饱和磁强度M_s= 12. 06 emu/ g～24. 38 emu/ g, 矫顽力H_c= 11 Oe～41 Oe。其环境稳定性明显优于纯聚吡咯。      

Preparation of α-Fe_2O_3 Nanodisks by Blocking the Growth of (001) Plane

Based on the difference of hydroxy group configuration on different planes of α-Fe2O3 nanoparticles, using the special adsorption and coordination of phosphate on the (001) plane of α-Fe2O3, well-crystallized and well dispersed α-Fe2O3 nanodisks with diameter of 150–200 nm and thickness of 40–80 nm were synthesized via a hydrothermal method. The magnetic properties of synthesized nanodisks were investigated. It was found that the nanodisks possessed a saturation magnetization (Ms) of 0.38 emu/g, a remanent ...     

Synthesis of nano-sized Fe–Co alloy powders by chemical solution mixing of metal salts and hydrogen reduction (CSM-HR)

Powder mixtures of (99.9% pure) FeCl₂ and CoCl₂ were used for synthesis of nanostructured Fe–Co alloy powders by chemical solution mixing and hydrogen reduction (CSM-HR). Nano-sized Fe–Co alloy powders were successfully fabricated by CSM-HR. The CSM-HR synthesized Fe–Co powder showed an ordered α′ phase with a particle size of 45 nm. The synthesized SMHR powder exhibited a coercivity force of 36 Oe and saturation magnetization value of 214 emu/g.     

Synthesis of the Fe3O4@SiO2@SiO2-Tb(PABA)3 luminomagnetic microspheres

In this paper, we describe the synthesis and characterization of a luminomagnetic microspheres with core-shell structures (denoted as Fe3O4@ SiO2 @SiO2-Tb(PABA)3). The luminomagnetic microspheres were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), and photoluminescence spectrophotometer (PL). The SEM observation shows that the microsphere consists of the magnetic core with about 400 nm in average diameter and silica shell doped with terbium complex with an average thickness of about 90 nm. It has a saturation magnetization of 15.8 emu/g and a negligible coercivity at room temperature and exhibits strong green emission peak from 5D4 --> 7F5 transition of Tb3+ ions. The luminomagnetic microspheres with good magnetic response and fluorescence probe property as well as water-dispersibility would have potential medical applications, such as time-resolved fluoroimmunoassay (TR-FIA), fluorescent imaging, and magnetic resonance imaging (MRI).     

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.     

Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.