Interactions between transition metals and defective carbon nanotubes

Interactions between 3d transition-metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and (5,5) carbon nanotube (CNT) with a vacancy defect are quantitatively characterized using first-principles calculations. The binding energies between CNT and transition metals are found to be significantly enhanced when vacancy defects are introduced into the CNT. For the defective CNTs doped with Sc, Cr and Zn atoms, the structures of defective CNTs are found to be intact. The doping of Ti, Mn, Cu, Fe, Ni and Co alternates the structures of defective CNTs. Among all 3d transition metals, only the ferromagnetic metal atoms Fe, Co and Ni form bonds with carbon atoms of CNT, suggesting the important role of magnetic exchange interaction in the p–d hybridisation between carbons and transition-metal atoms. The results also indicate that the 3d transition-metal atoms acting as substitutional defects can substantially modify the electronic structure of CNT. It is suggested that these stable CNT-metal systems could become promising engineering materials in many fields such as CNT devices for various spintronics applications and CNT metal–matrix composites.     

Synthesis of highly stable graphite-encapsulated metal (Fe, Co, and Ni) nanoparticles

Graphite-encapsulated metal magnetic nanoparticles have been attracted for biological applications because of their high magnetization of the encapsulated particles. However, most of the synthetic methods have limitations in terms of scalability and economics because of the demanding synthetic conditions and low yields. Here, we show that well-controlled graphite-encapsulated metal (Fe, Co, and Ni) nanoparticles can be synthesized by a hydrothermal method, simply by mixing metal source with sucrose as a carbon source. The saturation magnetization (Ms) values of Fe/C, Co/C, and Ni/C were 86.6, 43.8, and 113.1?emu/g, respectively. The Fe/C and Ni/C showed higher Ms values than bulk Fe₃O₄ (75.5?emu/g). The graphite-encapsulated metal nanoparticles showed good stability against acid and base environments.     

非晶丝微磁化线圈磁电阻抗效应研究

本文研究了铁基及钴基非晶态合金丝在由微磁经线圈所产生的轴向交变磁场的作用下所呈现的磁电阻抗效应，经出了一些测试结果，结果表明，微磁化线圈两端的电压信号峰－峰值随轴向外磁场Ｈｅ的增加而单调减少，钴基非晶丝可呈现巨磁电阻抗效应，利用该效应可制成新型磁敏元件及器件。     

Ab initio study of structure and magnetism of late transition metal oxide TMnOm clusters (TM = Fe, Co, Ni, n = 1, 2, m = 1-6)

We systematically investigate the structural and magnetic properties of late transition metal oxide clusters, TMnOm (TM = Fe, Co, Ni; n = 1, 2; m = 1-6) by using ab initio density functional theory approach. FenOm clusters prefer to adopt three dimensional configurations, while ConOm and NinOm clusters are apt to form planar structures. The O atoms are all atomic bonding to Fe atoms in the FenOm clusters, and are partly molecularly adsorbed to Co(Ni) in ConOm(NinOm) clusters, such as Co2O(5-6) (NiO3, and Ni2O(4-6)). The average binding energies per atom of TMnOm show a monotonous increase trend with the increase of O atoms for both n = 1 and 2 for TM = Fe, Co and Ni, and reach the peak at m = 4 for TM2Om and decrease a little bit afterwards. The odd-even magnetic oscillation is major trait with the peaks at odd and bottoms at even sizes for Fe2Om and Ni2Om (m = 2-6), respectively and large magnetic moments are found in Co2O3 and Co2O6.     

Formation of Extended Covalently Bonded Ni Porphyrin Networks on the Au（lll） Surface

The growth and ordering of {5,10,15,20-tetrakis(4-bromophenyl)porphyrinato}nickel(II) (NiTBrPP) molecules on the Au(111) surface have been investigated using scanning tunnelling microscopy, X-ray absorption, core-level photoemission, and microbeam low-energy electron diffraction. When deposited onto the substrate at room temperature, the NiTBrPP forms a well-ordered close-packed molecular layer in which the molecules have a flat orientation with the porphyrin macrocycle plane lying parallel to the substrate. Annealing of the NiTBrPP layer on the Au(111) surface at 525 K leads to dissociation of bromine from the porphyrin followed by the formation of covalent bonds between the phenyl substituents of the porphyrin. This results in the formation of continuous covalently bonded porphyrin networks, which are stable up to 800 K and can be recovered after exposure to ambient conditions. By controlling the experimental conditions, a robust, extended porphyrin network can be prepared on the Au(111) surface that has many potential applications such as protective coatings, in sensing or as a host structure for molecules and clusters.     

Unintended Phosphorus Doping of Nickel Nanoparticles during Synthesis with TOP: A Discovery through Structural Analysis

We report the discovery of unintentional phosphorus (P) doping when tri-n-octylphosphine (TOP) ligands are used in Ni nanoparticle synthesis, which is the most common method for monodisperse Ni nanoparticle synthesis. The nanoparticles appear pure face-centered cubic (fcc) Ni in X-ray diffraction despite the surprisingly high level (5 atomic %) of P. We find that the P doping follows a direct relationship with increased reaction time and temperature and that the P doping can be estimated with the degree of lattice expansion shown from a peak shift in the XRD spectrum. Through EXAFS modeling and density-functional (DFT) calculations of defect formation energies we find that the P atoms are preferentially located on the fcc lattice as substitutional dopants with oxidation state of zero. Magnetic and catalytic properties are shown to be greatly affected by this doping; DFT calculations show magnetization losses in the Ni system, as well as in Fe and Co systems. These findings are likely relevant for other metal syntheses that employ phosphine ligands.     

Magnetic properties of thin-film Co/Fe/Ni magnetic systems

The magnetic properties of Co/Fe/Ni thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. The results of x-ray diffraction measurements showed that all samples possessed a nanocrystalline structure. The magnetization curves and hysteresis loops were measured using the equatorial Kerr effect for two orientations of the external magnetic field. It is established that the Co/Fe/Ni thinfilm structures exhibit a planar magnetic anisotropy. The magnetic behavior of each layer in the initial inhomogeneous Co/Fe/Ni structure is substantially influenced by stray fields of the adjacent layers. This circumstance accounts for the complex shapes of hysteresis loops. The annealing in vacuum at T = 500°C renders Co/Fe/Ni thin-film structures magnetically hard compared to the initial state. The experimental results are explained by certain features of the microstructure of samples.     

Co0.5Fe2.5O4/ZrO2磁性纳米固体酸的合成与表征

将磁性基质Co0.5Fe2.5O4与ZrO2进行组装制备出磁性固体酸催化剂，采TEM,DTA,XRD,FTIR等手段对Co0.5Fe2.5O4/ZrO2磁性固体酸催化剂的结构和性能进行了研究，结果表明磁性基质的引入延迟了ZrO2的晶化以及ZrO2(t）相向ZrO2(m)相的转变，使ZrO2更加稳定，我们合成的Co0.5F2.5O4/ZrO2粒径在40nm左右，且具有良好的催化性能和适宜的磁学性能。     

静电纺丝法制备的Co0.6Ni0.3Cu0.1Fe2O4和Co0.6Ni0.3Zn0.1Fe2O4纳米纤维的结构及磁性能

采用静电纺丝技术制备出表面光滑、直径均匀的Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4/PVP和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4/PVP纳米纤维前驱丝,经500~900℃煅烧后得到Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维。用TG-DSC、XRD、SEM及VSM现代测试分析手段对Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的结构、形貌及磁学性能进行测试表征。结果表明:在空气气氛中经500~900℃煅烧后可得到纯尖晶石相、结晶度良好的纳米纤维或短纤维;当温度为700℃时,Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4和Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的形貌细长而光滑且直径相对均匀,大约为80nm;此时Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维则保有较高的剩磁比(M_r/M_s)及矫顽力,分别为0.56和1 088.87Oe。在500℃、600℃、700℃、800℃、900℃煅烧后,Co_(0.6)Ni_(0.3)Zn_(0.1)Fe_2O_4纳米纤维的饱和磁化强度分别比Co_(0.6)Ni_(0.3)Cu_(0.1)Fe_2O_4纳米纤维增大了14.5%、7%、16%、10.7%、8%,而矫顽力则分别降低了38%、51%、50%、46%、46.7%。两种纳米纤维的饱和磁化强度及矫顽力存在差异,为CoNi铁氧体在电磁方面的应用提供了很好的参考。     

超薄Ni81Fe19薄膜的各向异性磁电阻及磁性能

利用磁控溅射方法制备了一系列超薄Ta(5nm)/Ni81Fe19(20nm)/Ta(3nm)磁性薄膜。着重研究了基片温度、缓冲层厚度对Ni81Fe19薄膜各相异性磁电阻(AMR)及磁性能的影响。利用X射线衍射仪分析了薄膜结构、晶粒取向;用四探针技术测量了薄膜的电阻率和各向异性磁电阻;用FD-SMOKE-A表面磁光克尔效应试验系统测量了薄膜的磁滞回线。结果表明:在基片温度为400℃时制备的Ni81Fe19薄膜具有较大的各向异性磁电阻效应和较低的磁化饱和场,薄膜最大各向异性磁电阻为3.5%,最低磁化饱和场为739.67A/m。基片温度为500℃制备的薄膜,饱和磁化强度Ms值最大。随着缓冲层厚度x的增加,坡莫合金薄膜的AMR值先变大后减小,在x=5nm时达到最大值。     

Magnetic Ordering and Exchange Interaction of Laves Compounds Sm0.9Pr0.1（Fe1—xCox）2

Structure,magnetic properties and magnetostriction of Sm0.9Pr0.1(Fe1-xCox)2 compounds have been investi-gated by means of X-ray diffraction,a.c. initial susceptibility, extracting sample magnetometer,Mossbauer spec-troscopy and standard strain gauge techniques.The lattice parameter a of the MgCu2-type Laves compounds Sm0.9Pr0.1(Fe1-xCox)2 decreases nonlinearly with increasing Co concentration,deviating from the Vegardˊs law.Curie temperature Tc increases initially from 668 K for x=0 to 694 K for x=0.2 and then decreases to 200 K for x=1.0.The saturation magnetization Ms at temperatures 1.5K, 77K and 300K have the same variation tendency as the composition dependence of Curie temperature,in consistence with rigid-band model.The easy magnetization direction(EMD) od Sm0.9Pr0.1(Fe1-xCox)2 lies along [111] direction in the range x≤0.6,and changes to [110] for x=0.8 ,while Sm0.9Pr0.1(Fe1-xCox)2 stays in the paramagnetic state at room temperature.The composition dependence of the average hyperfine field,Hhf,demonstrates a similar variation tendency as that of the saturation magnetiza-tion Ms and Curie temperature Tc .The spontaneous magnetostricton λ111 increases with increasing Co content.The saturation magnetostriction λs decreases monotonically with increasing x,which is caused by the increase of magnetostriction constant λ100 with opposite sign to that of λ111.A two-sublattice model has been proposed to understand the intermediate region between the [111]and [110] spin configurations ,which can also be used to explain the temperature dependence of magnetization.     

Spin polarization measurement of homogeneously doped Fe(1-x)Co(x)Si nanowires by Andreev reflection spectroscopy

We report a general method for determining the spin polarization from nanowire materials using Andreev reflection spectroscopy implemented with a Nb superconducting contact and common electron-beam lithography device fabrication techniques. This method was applied to magnetic semiconducting Fe(1-x)Co(x)Si alloy nanowires with x? = 0.23, and the average spin polarization extracted from 6 nanowire devices is 28 ± 7% with a highest observed value of 35%. Local-electrode atom probe tomography (APT) confirms the homogeneous distribution of Co atoms in the FeSi host lattice, and X-ray magnetic circular dichroism (XMCD) establishes that the elemental origin of magnetism in this strongly correlated electron system is due to Co atoms.     

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。     

Synthesis of Nano Crystalline Ni and Fe by Levitational Gas Condensation Method

Nanocrystalline Ni and Fe were synthesized by the levitaional gas condensation (LGC) method using wire feeding (WF) and micron powder feeding (MPF) systems. The magnetic properties have been characterized using a vibrating sample magnetometer (VSM) and Moumlssbauer spectroscopy. The X-ray diffraction and saturation magnetization results indicate the small amount of oxidized phases such as amorphous NiO and Fe₃O₄ on the surface of metal powders. The size and shape of the nano powders were investigated by transmission microscopy (TEM). It was found that particles have a mean crystallite size about 22 and 24 nm for Fe and Ni. The surface effect might influence the magnetic hysterisis behavior of Ni and Fe     

Observation of Exchange Interaction in Iron(II) Spin Crossover Molecules in Contact with Passivated Ferromagnetic Surface of Co/Au(111)

Spin crossover (SCO) complexes sensitively react on changes of the environment by a change in the spin of the central metallic ion making them ideal candidates for molecular spintronics. In particular, the composite of SCO complexes and ferromagnetic (FM) surfaces would allow spin-state switching of the molecules in combination with the magnetic exchange interaction to the magnetic substrate. Unfortunately, when depositing SCO complexes on ferromagnetic surfaces, spin-state switching is blocked by the relatively strong interaction between the adsorbed molecules and the surface. Here, the Fe(II) SCO complex [Fe^II(Pyrz)₂] (Pyrz = 3,5-dimethylpyrazolylborate) with sub-monolayer thickness in contact with a passivated FM film of Co on Au(111) is studied. In this case, the molecules preserve thermal spin crossover and at the same time the high-spin species show a sizable exchange interaction of > 0.9 T with the FM Co substrate. These observations provide a feasible design strategy in fabricating SCO-FM hybrid devices.     

Probing interfacial properties of ferromagnetic/insulator bilayers with X-ray spectroscopies: Application to Fe,Co, Mn/MgO(0 0 1) interfaces

Electronic and magnetic properties of bcc Co, Fe and Mn(0 0 1) epitaxial monolayers in contact with a single-crystalline MgO(0 0 1) film were studied using X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements. The XPS and XAS analysis clearly evidenced the weak hybridization between the MgO barrier and Fe or Co. On the contrary, a net oxidization of the Mn layer in contact with the MgO layer was observed. The magnetic properties were characterized by probing the XMCD signal of a unique atomic plane of transition metal in contact with MgO. The total magnetic moment per Co and Fe atoms were observed to increase compared to the bulk at the metal/oxide interface. Finally, Mn at the interface with MgO does not present any ferromagnetic behavior. This was assumed to be a consequence of the Mn oxidization.     

Magnetism and solid solution effects in NiAl (40% Al) alloys

The solid solution effects of ternary additions of transition elements in intermetallic Ni–40% Al were investigated by both experimental studies and theoretical calculations. Co solute atoms when sitting at Ni sublattice sites do not affect the lattice parameter and hardening behavior of Ni–40Al. On the other hand, Fe, Mn, and Cr solutes, which are mainly on Al sublattice sites, substantially expand the lattice parameter and produce an unusual solid solution softening effect. First-principles calculations predict that these solute atoms with large unfilled d-band electrons develop large magnetic moments and effectively expand the lattice parameter when occupying Al sublattice sites. The theoretical predictions were verified by both electron loss-energy spectroscopy (EELS) analyses and magnetic susceptibility measurements. The observed softening behavior can be explained quantitatively by the replacement of Ni anti-site defects (potent hardeners) by Fe, Mn, and Cr anti-site defects with smaller atom size mismatch between solute and Al atoms. This study has led to the identification of magnetic interaction as an important physical parameter affecting the solid solution hardening in intermetallic alloys containing transition elements.     

Influence of different conducting substrates on magnetic properties of electrodeposited Ni–Fe thin films

Electrodeposition of Ni–Fe soft magnetic alloy on copper and stainless steel substrates was performed in chloride bath. The deposition parameters such as current density, pH, temperature and deposition time have been investigated. From the investigation the optimized deposition parameters were current density 3.5 mA/cm², pH 3, temperature 30 °C and deposition time 15 min. The Ni–Fe magnetic alloys deposited on copper and stainless steel substrates under optimized deposition parameters are subjected to various characterizations. The structural and surface morphology of the Ni–Fe films were detected by using X-ray diffractogram (XRD) and scanning electron microscope (SEM) respectively. The constituents in the films were determined by energy dispersive X-ray spectroscopy (EDAX) technique. The magnetic properties such as the coercivity (H_c) and saturation magnetization of the films were studied with the help of vibrating sample magnetometer (VSM). From the magnetic studies it is concluded that the grain size are create a considerable impact on magnetic behavior of the films on both the substrates. The films prepared on stainless steel substrate of 0.1 M concentration at optimized deposition parameters exhibits higher coercivity (5010 Oe) which seems to be ideal for magnetic sensor applications.     

Magnetic properties of binary Cu50–(Ni, Fe and Co)50 alloys prepared by ball milling and isothermal annealing

The magnetic properties of Cu–Ni, Cu–Fe and Cu–Co binary alloys prepared by ball milling and subsequent isothermal annealing have been investigated systematically. A detailed microstructural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopic (HRTEM) analysis shows that single phase Cu–Ni solid solution formed by isothermal annealing of ball-milled Cu–Ni powder blend deteriorates the magnetic properties. In contrast, isothermal annealing of Cu–Fe and Cu–Co powder blends resulted into significant improvement of magnetic properties due to precipitation of Fe and Co from the respective supersaturated solid solution. Dispersion of Co nanoparticle in Cu matrix yielded the most attractive magnetic properties.     

The dependence of the magnetic properties of non-magnetostrictive NiFeCo films on the deposition conditions of aluminium underlayers

Results are presented which describe the effect of the deposition parameters of aluminium underlayers on the magnetic properties of non-magnetostrictive NiFeCo films. Three aluminium film deposition parameters were considered: evaporation rate, substrate temperature and film thickness. The effects of these parameters on the structure of the aluminium film and on the coercivity, angular dispersion, anisotropy field and saturation magnetization of the subsequent magnetic film in the thickness range 0.06–0.5 μm are reported.A correlation of the angular dispersion with underlayer grain size was established experimentally and is explained in terms of a linear micromagnetic theory of dispersion.