Synthesis,structure and stability of MoCl5-graphite intercalation compounds

The mechanism for the synthesis of MoCl₅-graphite intercalation compounds (MoCl₅-GICs) with stage-1 structure, which was successfully done in the presence of either MoOCl₃ or MoO₃ with MoCl₅, was discussed. The formation of reactive chlorine gas was supposed to be important for the formation of stage-1 structure. Well-ordered stage structures along the c-axis were easily obtained in MoCl₅-GICs synthesized from natural graphite and also from highly-crystallized graphite films. From detailed observation by STM/AFM on stage-4 GICs, a superstructure in the graphite basal plane (in-plane structure) was found in large intercalated domains with an area of more than 150 μm², having a hexagonal symmetry of which axes rotated by about 30° from graphite axes and having a periodicity of 1.9 nm. The boundaries between large intercalated and non-intercalated domains consisted of linear segments which were parallel to certain crystallographic axes of graphite, but those between small intercalated domains with the area less than 100 nm² and non-intercalated domains were irregular. These MoCl₅-GICs were experimentally shown to have very high stability in various liquids, all of which can dissolve MoCl₅ itself. Even in boiling water, the compounds prepared from graphite hosts with a flake size as large as 400 μm showed only a trace of decomposition of GICs, but those from a flake size as small as 10 μm were decomposed.     

Magneto-microstructural coupling during stress-induced phase transformation in Co49Ni21Ga30 ferromagnetic shape memory alloy single crystals

The present study reports on direct magneto-microstructural observations made during the stress-induced martensitic transformation in Co₄₉Ni₂₁Ga₃₀ alloy single crystals with optical, scanning electron, and magnetic force microscopy (MFM). The evolution of the microstructure and the associated magnetic domain morphology as a function of applied strain were investigated in the as-grown condition and after thermo-mechanical training. The results demonstrated that the stress-induced martensite (SIM) evolves quite differently in the two conditions and depending on the martensite formation mechanisms, the magnetic domain configuration was dissimilar. In the as-grown crystals two twin-related martensite variants were formed and the growth of these twin variants resulted in large strain. After thermo-mechanical training a morphology similar to a self-accommodating martensite structure was present at the initial stages of the transformation and thereafter martensite reorientation (MR) was the main transformation mechanism. The magnetic domains were found to be superimposed on the nano-scaled martensite twins in the as-grown condition, whereas training brought about the formation of domains on the order of a few microns without showing the one-to-one correspondence between domains and the twin structure. After the thermo-mechanical training detwinning at high-strain levels led to the formation of stripe-like domain structures. The ramifications of the results with respect to the magneto-microstructural coupling that may cause the magnetic shape memory effect (MSME) in Co–Ni–Ga alloys under constant external stress is addressed.     

Cooling rate induced variation in microstructure and magnetic structure of Nd60Fe30Al10 glass forming alloy

Cooling rate induced variation in microstructure and magnetic structure was investigated in the as-cast Nd₆₀Fe₃₀Al₁₀ alloy. Because the cooling rate was different from the periphery to the center regions, apparent evolution from a full amorphous to a partial precipitated crystalline structure was observed in one as-cast sample. Corresponding to different microstructures, two magnetic domain structures, i.e. fine strip-like domains in sub-micron scale and sunflower-like domains in micron scale, were observed at the periphery and the center of a cross section, respectively. The variation of magnetic properties was discussed in the view of exchange interaction coupling.     

钴基非晶薄带交换偏置现象稳定性和可控性的研究

钴基(Co58Fe5Ni10Si11B16)非晶薄带在一定温度范围内做热磁处理之后,由于薄带内有少量磁性较硬结晶相析出,其磁矩对非晶软磁基体的钉扎作用使样品出现交换偏置行为。在研究过程中采用X射线衍射仪、高分辨透射电镜表征样品相组成及微观结构,利用冲击检流测量法测试其磁滞回线,通过扫描探针显微镜观测薄带表面磁畴,由此深入分析内在磁矩配置情况。结果表明,在利用横向冲击场调控钴基薄带交换偏置行为的过程中存在临界场。当横向冲击场低于临界场时,结晶相磁矩几乎不受其影响,交换偏置行为呈稳定状态;而大于临界场时,结晶相磁矩在其冲击作用下按自由能最小原则重新配置,交换偏置行为可通过调节横向冲击场的大小有效调控。     

SEM investigation of the magnetic domain structure of sintered SmCo5 permanent magnets

The paper presents scanning electron microscopy (SEM) study of the magnetic microstructure of anisotropic sintered SmCo₅ permanent magnets. Observations were made in the thermally demagnetized state of the magnets at the surfaces both perpendicular and parallel to the alignment axis. Magnetic domains were revealed using the technique of type-I magnetic contrast (for the first time) and the colloid-SEM method. The domain structure consists of main domains (which extend through the whole grain thickness) and surface domains of reverse magnetization (reverse spikes). The main domains form a maze pattern near the surface perpendicular to the alignment axis. The reason for the presence of the maze domain structure and reverse spikes at the surface perpendicular to the alignment axis is the reduction in the magnetostatic energy at the cost of a larger total Bloch wall area. Investigations carried out on the surface parallel to the alignment axis allowed to obtain much better insight into the orientation of grains.     

Crystalline structures and misfit strain inside Er silicide nanocrystals self-assembled on Si(001) substrates

The morphology and crystalline structure of Er silicide nanocrystals self-assembled on the Si(001) substrate were investigated using scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). It was found that the nanowires and nanorods formed at 630?°C has dominant hexagonal AlB(2)-type structure, while inside the nanoislands self-organized at 800?°C the tetragonal ThSi(2)-type structure is prevalent. The lattice analysis via cross-sectional high-resolution TEM demonstrated that internal misfit strain plays an important role in controlling the growth of nanocrystals. With the relaxation of strain, the nanoislands could evolve from a pyramid-like shape into a truncated-hut-like shape.     

Highly organized crystalline monolayer of a semi-fluorinated alkane on a solid substrate obtained by spin-coating

We have obtained a 40 nm parameter crystalline monolayer of a semifluorinated alkane on a silicon wafer using the spin-coating technique. Its structure, analyzed by atomic force microscopy (AFM), is identical to that recently observed at the air-water interface, showing the existence of hexagonal nanodomains, organized on a long range order hexagonal lattice of a few tens of nanometers lateral parameter. Considering AFM images published on films transferred by the usual Langmuir-Blodgett method, one can note that the monolayers form locally ordered rounded domains. With our procedure, the original highly organized large crystalline structure is recovered.     

PMNT单晶电畴结构随组分与结构的变化

利用多种方法观察了弛豫型铁电单晶ＰＭＮＴ中电畴结构随组分与结构的演变过程与特征．观察发现,在ＰＭＮ－ＰＴ的三方相区内,随ＰＴ含量的增加,电畴结构表现出微畴一（亚微畴）－不规则宏畴一规则宏畴转变历程;在三方－四方相变中,非１８０°电畴发生７１°（或１０９°）宏畴－９０°宏畴的转化,同时电畴图像变得更为规则．根据不同组分ＰＭＮＴ电畴的显示特征,提出晶体的最大双折射率可以作为度量其弛豫性强弱的光学参数．观察到了电畴的分布不均匀与多级结构现象,前者与组分或结构的起伏有关,后者与多期式马氏体转变有关．本文还分析了偏光显微镜、ＤＩＣ、ＳＥＭ、ＳＥＡＭ等观察方法中电畴的成像特征．     

3D magnetic characterization of nanocrystalline cobalt thin films by combined magnetic force and Lorentz microscopy

Thin films of cobalt and cobalt-based compounds are recently popular for magnetic recording media because of their high recording density and great magnetic properties. Many techniques exist to image magnetic structures in thin films, nevertheless, none of them can furnish complete information about the magnetic details. In the present work the combined use of the information obtainable with Lorentz microscopy, performed in a transmission electron microscope (TEM), and of an atomic force microscope (AFM) working in the magnetic mode (MFM, magnetic force microscopy), both performed on the same specimen area, enabled, in a easy way, the study of the 3D magnetic structure of domains, of single cross-ties, the location of Bloch lines within a domain wall and the magnetic structure of magnetisation ripples. The 3D magnetic structure and contrast of nanocrystalline thin films of cobalt (100 nm thick), prepared by evaporation in high vacuum, were investigated at a spatial resolution of tens of nanometers.     

Observation of magnetic domains in NdCo5using an electro-etching technique

Magnetic domains have been observed in NdCo5using an electro-etching technique. Electro-etching in an applied magnetic filed yields a surface record of the field related domain structure that can be viewed using a light microscope without polarizers. High contrast between oppositely magnetized domains can be obtained on surfaces both parallel and perpendicular to thecaxis. The effect of increasing the magnetic field to the point where circular or spike domains are obtained is shown and other etching variables are discussed     

The magnetic domain and properties of amorphous ribbons

The magnetic behavior of Fe78B13Si9amorphous ribbons has been investigated by means of observations of the magnetic domains and measurements of the magnetization curves and core losses. The Fe78B13Si9samples, which were 10 mm wide and approximately 25 μm thick, were annealed under 10^-3torr, from 200°C to 425°C, in a dc magnetic field of 1600 A/m directed along the ribbon length. The magnetic domains formed simple 180° patterns parallel to the ribbon length, and the ribbons showed the best quality magnetic properties after magnetic field annealing at 350°C. After annealing below this temperature, the domain patterns and magnetic properties of the samples were similar to those of the as-cast ribbons. In contrast, after a magnetic field annealing above 400°C, the domain patterns distorted, and the magnetic properties deteriorated. The resultant air-pockets and holes on the surfaces of the amorphous ribbons trapped the magnetic domains and caused distorted domain patterns. In the stress pattern observed on the convex side of a bent amorphous ribbon, the domain width narrowed as the bending radius was increased.     

Mechanism of Residual Stress Reduction in Low Alloy Steel by a Low Frequency Alternating Magnetic Treatment

Residual stress reduction in low alloy steel by a low frequency alternating magnetic treatment and its mechanism were investigated. Experimental results revealed that average stress reductions of 20%-24% were obtained in the welded samples. Moreover, compared with the zones with lower initial stress levels, more remarkable stress reductions were obtained in the stress concentration zones. The microstructures and magnetic domains were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Based on the analysis of the microstructure and magnetic domain changes, the mechanism of stress reduction by the magnetic treatment has been concluded: (1) the magneto-plastic deformations mainly due to the more uniform redistribution of dislocations are the fundamental cause of stress relaxation; and (2) surface topography is also proved to affect the magnetic treatment results to some degree by influencing magnetic domains.     

Ferromagnetic domains in EuS investigated by low-temperature Lorentz microscopy

Thin films of EuS, prepared by electron beam evaporation, were investigated by Lorentz microscopy in a special low-temperature object stage. In the thermally demagnetized state of an isotropic film, a multidomain configuration is observed with the smallest detectable domain size being about 200 nm. In the ac-demagnetized state, the domain configuration is similar to the configuration during a magnetization reversal. The magnetization reversal in an isotropic film starts by nucleation of small domains at inhomogeneities in the film, mostly at the edges, and by the growth of the nuclei. The domain configuration is strongly influenced by mechanical stress. The mechanical stress has an effect on the magnetization reversal of EuS similar to a field-induced anisotropy in NiFe films. The walls in EuS films down to a film thickness of 7 nm are Bloch walls.     

Effect of thermal stress on magnetic domain patterns of multiferroic Bi1-xDyxFeO3 thin films

Effect of temperature on magnetic domain structure of Bi_0.7Dy_0.3FeO₃ (BDFO) multiferroic thin films is studied in situ using magnetic force microscopy (MFM). Initially, as the temperature increases the domains start aligning from irregular to more distinct stripe pattern. However, above 250 °C, the domain alignment is disturbed. The systematic change in the domain configuration with temperature, suggests a strong thermal history of the system. The randomness in domain alignment caused above 250 °C is correlated to internal stress developed during ferromagnetic to paramagnetic phase transition occurring in BDFO. Indirect experimental evidence is given to support the explanation based on stress.     

Micromagnetic Structure of Co-Rich Amorphous Microwires

1. IntroductionSince the discovery of amorphous materials theirmagnetic prOPerties have been eXtensively studieddue to a great deal of laterest for fundamental investigations and their enormous potelltial in technological applications (in sensors, transducers, magnetic screens). Co-rich amorphous wires are promising candidates for a variety of sensor applications.It is knownlll thst some importal magnetic characteristics for technical applications (for example,low field magnetoresistance, mag…     

Magnetization reversal and microstructure in polycrystalline Fe50Pd50 dot arrays by self-assembling of polystyrene nanospheres

Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe₅₀Pd₅₀ thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L1₀ phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity.     

First-Principles Investigation of Electronic Structure Features of TbOFeAs Compound

We report a theoretical investigation on the electronic and magnetic properties of rare-earth pnictide parent compound, such as TbOFeAs. Employing first-principles method supplemented by the local spin density approximation (LSDA), we discuss the electronic structure with the incorporation of the role of Coulomb on-site repulsion (U) of Tb 4f states as well as the spin-orbit (SO) coupling on the magnetic and nonmagnetic phases. For ferromagnetic (FM) and antiferromagnetic (AFM) phases, we have determined the spin and orbital magnetic moments of Tb ions and confer the significance of the spin-orbit interaction of Tb 4f states in this parent compound. In the FM state, the reduction of Fe moment is about a factor of 3.5 with respect to AFM configuration. The most energetically favorable state is AFM configuration. Our theoretical findings surmise that the magnetic moments on Fe sites carry an AFM order. Based on LSDA + U + SO approximation, we infer that the Tb magnetic moments also carry an AFM order, albeit the spin Tb sites in TbO layer possess the same orientation as the Fe spins in FeAs layer. With the incorporation of on-site Coulomb repulsion and spin-orbit interaction in AFM state, the Fe 3d states are large near the Fermi level and this phase is illustrating a metallic behavior. Moreover, the Fermi surface topology and nesting features are presented.     

Imaging domains of hard magnetic materials by SEM and MFM

The paper deals with observation of the magnetic domain structure of hard magnetic materials by the colloid-scanning electron microscopy (colloid-SEM) technique and the magnetic force microscopy (MFM) method. The specimens studied were anisotropic sintered Nd-Fe-B-based and SmCo₅ magnets, produced by powder metallurgy route. Observations of the magnetic microstructure were carried out in the thermally demagnetized state of the magnets at the surface perpendicular to the alignment axis. The domain structure is of complicated character. The coarse domain pattern consists of the main domains (forming a maze pattern near the specimen surface) and surface reverse spikes. Besides the coarse domain structure, the presence of fine scale surface domains is revealed by MFM.     

In-situ examination of the selective etching of an alkanethiol monolayer covered Au{111} surface

An examination of the selective etching mechanism of a 1-alkanethiol self-assembled monolayer (SAM) covered Au{111} surface using in-situ atomic force microscopy (AFM) and molecular resolution scanning tunnelling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au{111} surface and typically contains nanoscale non-uniformities such as pinholes, domain boundaries and monatomic depressions. During etching in a ferri/ferrocyanide water-based etchant, selective and preferential etching occurs at SAM covered Au(111) terrace and step edges where a lower SAM packing density is observed, resulting in triangular islands being relieved. The triangular islands are commensurate with the Au(111) lattice with their long edges parallel to its [11¯0] direction. Thus, SAM etching is selective and preferential attack is localized to defects and step edges at sites of high molecular density contrast.