Rotatable magnetic anisotropy in epitaxial ferrite layers

Magnetic domain structure and magnetic anisotropy were studied in monocrystalline epilayers of Mg0.9Mn0.3Fe1.8O4ferrite. The layers, several micrometers thick, were obtained by a CVD method on monocrystalline MgO substrates. Domain observations were performed by the Bitter's method. Magnetic anisotropy measurements were performed by torque and FMR methods. In the demagnetized state, a typical stripe structure of 2.0 to 2.8 μm period was observed. From the domains behavior in the in-plane magnetic fields it was found that in these epilayers the rotatable anisotropy was present. The existence of this anisotropy was confirmed by torque measurements in small in-plane fields. The magnetic parameters characterizing these layers are: 4ΠM = 3500 Gs, K1= - 2.2 × 10⁴ergs/cc, KN= 2.3 × 10⁵ergs/cc.     

The effect of reaction temperature on the particle size, structure and magnetic properties of coprecipitated CoFe2O4 nanoparticles

Magnetic nanoparticles of cobalt ferrite have been synthesized at different temperatures without any subsequent heat treatment. The particle size, crystal structure and magnetic properties of as-synthesized particles were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and vibrating sample magnetometer. The nanoparticles are of cubic spinel structure and equiaxial shape. The average size of nanoparticles increases with the increase of reaction temperature. Magnetic properties of nanoparticles show strong dependence on the particle size. A maximum coercivity of 3267 Oe and a maximum remanence ratio of 0.58 are obtained from the sample synthesized at 80 °C.     

Substrate facet replication by epitaxial magnetic garnet films

Epitaxial ferrimagnetic garnet films were deposited on Czochralski grown single crystal gadolinium gallium garnet substrates containing faceted regions. Films grown by both chemical vapor deposition (CVD) and liquid phase epitaxy (LPE) were studied. Lattice parameter distributions were determined by the method of X-ray double crystal topography with rocking curve analysis. The demagnetized domain strip width, magnetization, and characteristic length were measured in a CVD film in regions inside and outside the substrate facets. It was determined that replication of the substrate facets by the epitaxial film is accomplished by a difference in film stress. This stress difference arises from the lattice parameter difference between the faceted and unfaceted regions of the substrate. These results lead to the establishment of a criterion for allowable lattice parameter variation in substrates to be used for magnetic bubble domain films with stress induced anisotropy.     

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.     

Characterizing the Exchange Interaction of Sm-Co/Co （and Fe65Co35） Magnetic Films

Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co （and Fe65Co35） magnetic films was characterized by measuring static （mr（H）） and demagnetized （md（H）） remanence curves. According to conventional method： δm（H）=md（H） - [1 - 2mr（H）], the exchange interaction was evaluated. The switching fields H′p and Hp, at which static （mr（H）） and demagnetized （md（H）） remanence show the fastest change, were identified. The relative ratio η=Hp-H′p/Hp of switching fields H′p and Hp has a linear relationship with the maximum value δmmax of δm（H） curves, proposing an alternative way to characterize the exchange interaction.     

Study of magnetic properties of thin cobalt films deposited by chemical vapour deposition

Chemical Vapour Deposition (CVD) of cobalt was deposited from a liquid source precursor of cobalt tricarbonyl nitrosyl (Co(CO)₃NO) on to oxidised < 100 > silicon wafers. The cobalt layers were deposited at 450∘C at 1.5 torr chamber pressure of hydrogen for 15 min processing time with various precursor flow rates. X-ray diffraction studies of the cobalt films reveal both hcp and fcc peaks. The vibrating sample magnetometer (VSM) yields coercivity (Hc) 167 Oe and 364 Oe for 46 nm and 30 nm thickness layers respectively at room temperature and squareness (S) M_r/M_s (remanence/saturation of magnetisation) value of ∼ 1. The study of magnetic properties of the cobalt suggests that magnetisation is dependent on grain size and therefore thickness. The grain size was observed by atomic force microscopy (AFM). Magnetic images were observed by magnetic force microscopy (MFM) and analyzed in terms of domain structure. The surface domain structure was recorded with the tip lift height 100 nm so that the magnetic interactions arising produced the topography effect. Where there is repulsive interaction the intensity is recorded as a bright region and where the interaction is attractive the intensity is recorded as a dark region.     

LPE growth of iron garnets containing Ge4+ and Si4+ for bubble applications

Magnetic garnet films containing Ca²⁺ plus Ge⁴⁺ and/or Si⁴⁺ are of interest for bubble device applications. Extensive property variations can be obtained in compositions having a lattice constant essentially the same as GGG and suitable films are easily grown using conventional LPE dipping techniques. Films of Y_3?xCa_xFe_5?xGe_xO₁₂, where x = 0.0 to 3.0, have been prepared on GGG substrates and have bubble diameters from sub-micron sizes to over 150 μm. Preferred device materials having moments between ～ 200 and 500 gauss with bubble diameters of ～ 1 to 6 μm have stable bubble properties from well below ?10 to at least 120°C and mobilities of ～ 2000 cm/sec/Oe. The effect of growth conditions and melt composition on bubble properties are discussed.     

铁纳米粉体的磁性能研究

为了研究铁纳米粉体材料与常规材料在磁性能方面的不同,采用阳极弧放电等离子体方法制备了铁纳米粉体。利用X射线衍射(XRD)、透射电子显微镜(TEM)和振动样品磁强计(VSM)等测试手段对样品的形貌、晶体结构、粒度、磁性能进行表征,并对振动样品磁强计测量静态磁特性的原理进行了分析。测试结果表明,样品呈规则的球形链状分布,表面光洁,平均粒径为39nm,粒径范围分布区间窄,晶体结构为bcc结构的晶态;纳米结构材料与常规材料在磁结构上有差别,铁纳米粉体的饱和磁化强度Ms为53emu/g,剩余磁化强度Mr为1.5emu/g,矫顽力Hc为32.2Oe。     

Surface plasmon mediated interference phenomena in low-q silver nanowire cavities

Optical excitation of surface plasmons in wet-chemically grown monocrystalline silver nanowires ( approximately 100 nm diameter and up to a few tens of micrometers length) is studied by broadband imaging spectroscopy. Surface plasmons excited by an incident light beam in the so-called Kretschmann-Raether configuration give optical interference phenomena in the spectral domain. These spectral oscillations are interpreted in terms of Fabry-Perot cavity modes for surface plasmons in silver nanowires and allow for a direct experimental determination of the surface plasmon group velocity and cavity losses.     

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。     

Synthesis and characterization of carbon nanoribbons and single crystal iron filled carbon nanotubes

Carbon nanoribbons and single crystal iron filled multiwall carbon nanotubes (MWCNTs) have been synthesized by simple pyrolysis technique. SEM investigation shows that the material consist mainly carbon nanoribbons and carbon nanotubes (CNTs). X-ray diffraction (XRD), electron energy loss spectroscopy (EELS), electron energy dispersive X-ray (EDX), transmission electron miscroscopy (TEM) and highresolution transmission electron miscroscopy (HRTEM) studies reveal carbon nanotubes are filled with α-Fe. Closer inspection of HRTEM images indicated that the bcc structure α-Fe nanowires are monocrystalline and Fe (1 1 0) plane is indeed perpendicular to the G (0 0 2) plane, whereas orientation of (0 0 2) lattice planes of carbon nanoribbon is perpendicular to the axis of growth. Magnetic properties studied by superconducting quantum interference device (SQUID) at 300 K and 10 K exhibited coercivity of 1037 Oe and 2023 Oe. The large coercitivity is strongly attributed to the small size monocrystalline single phase α-Fe, single domain nature of the encapsulated Fe crystal, magnetocrystalline shape anisotropy and ferromagnetic behaviour of localized states at the edges of the carbon nanoribbons.     

Electroplated hard magnetic material and its application in microelectromechanical systems

We describe the preparation of CoNiMnP-based permanent-magnet material using several sulfate and chloride solutions. We studied eight samples, and all the samples show vertical magnetic anisotropy. Sample8, which was electroplated from a low-concentration chloride solution and under external magnetic field, demonstrates the best magnetic properties with coercivity 2632 Oe, remanence 0.20 T, and maximum magnetic energy 10.185 kJ/m/sup 3/. An array structure can avoid the stress between the electroplated layer and the seed layer. The electroplated Co/sub 0.8/Ni/sub 0.1174/Mn/sub 0.0062/P/sub 0.0762/ permanent magnet has potential for bidirectional actuators in micro-electromechanical systems.     

Magnetoelastic effects in amorphous Fe40Ni40P14B6alloys

The influence of compressive, tensile, and bending stresses on the magnetization processes, anisotropy energy, and remanence of an as-quenched amorphous Fe40Ni40P14B6ribbon has been studied. The magnetostriction constant has been obtained from the variation of the susceptibility with the applied compressive stress. To better understand the results, domain structures have been observed by using the Bitter technique. Our results show that the Metglas ribbon has a central region with compressive stress, while the edge regions have tensile stress. So, the influence of these regions on the magnetization processes will be very different according to the applied stress.     

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.     

Horizontal Bloch line motion in magnetic bubble materials

Horizontal Bloch line (HBL) motion in magnetic bubble materials is studied by comparing experimental results with a numerical simulation of domain wall motion. The present theory of HBL motion is reviewed and then extended by allowing both the wall position q and azimuthal angle φ to vary with position through the film thickness z. The resulting equations of motion are solved numerically for q(z, t) and φ(z,t), and the solutions are compared with results from wall oscillation experiments. In these experiments, a bias field pulse is used to produce a step change in the equilibrium position of stripe domain walls in the presence of small in-plane fields parallel to the walls, Hx= 0 Oe, 4 Oe, and 10 Oe. The wall response is then measured by using a sampling photometric technique. Good quantitative agreement is found between numerical and experimental results, so that the internal processes that occur during wall motion can be inferred from the calculation. Changes in q through the film thickness play an important role in HBL motion. During the initial response, the twist structure φ(z) is similar to the initial static structure and the wall surface is relatively flat. A backward bulge soon forms near one of the film surfaces as a result of local dynamic properties. This bulge provides the additional torque necessary to form the HBL. The bulge accompanies the HBL as it moves toward the opposite film surface and provides the torque necessary for HBL propagation. Internal vibrations of the wall surface are excited by the bulge and produce irregular motion of the average wall position. Punch-through occurs when the HBL reaches the opposite surface. During this process, φ at the film surface rotates rapidly from π/2 to 3π/2. At the same time the wall section in this region moves backward. As a result, the average wall position is essentially stationary during punch-through.     

Some characteristics of ion-implanted bubble chips

The relations between the position of charged walls and the bubble motion around propagation circuits are discussed. Long walls which extend between adjacent propagation loops are revealed by the Bitter technique. The examination of the domain structure in the implanted layer shows the existence of a magnetic gradient which is a function of the distance from the propagation circuits. The switching of magnetization in particular directions of the in-plane field is reported and correlated with the bubble movement. An additional easy axis is observed along the circuits due to shape anisotropy. Propagation margins are very similar to those obtained with permalloy circuits. Fabrication technology as well as design of 16 μm period circuits is discussed. Nucleation and transfer have been achieved with currents in the range of 50 mA to 200 mA. Phase margins of about a quarter of a period are found, and bias field margins fall between 10 and 15 Oe.     

The temperature dependence of the domain structure of uniaxial single crystals with high-anisotropy field

The temperature dependence of the domain structure of single crystals of uniaxial ferrimagnetic oxides with high-anisotropy field in the SrO(6 - x)Fe2O3xAl2O3compositional series, withx = 1.8and 2.4, was investigated. The domain configurations of thermally and/or ac field demagnetized states and the changes in dc and ac fields were observed by means of the colloid technique using a suspension in paraffine oil. The temperature dependence of the wall energy density between room temperature and the Curie point (270°C) of the compound withx = 1.8was computed using the temperature dependence of the saturation magnetization and the domain width for the Kittel-like domain structure. It has been found that the room temperature domain structure of the compound withx = 2.4depends upon the mode of demagnetization, i.e., thermally or in the ac field. The ac demagnetized states are more stable than the thermally demagnetized ones. The samples exhibit a room temperature memory of the previous magnetization, which decreases with rising temperature. This memory is completely lost after heating at 400°C. The peculiarities of the temperature dependence of the domain structure and magnetic behavior on thermal cycling are explained by considering the existence of magnetic inhomogeneities within the crystal.     

Hard magnetic two-phase Co-Cu thin films

The magnetic properties of sputtered films of 25 Co-75 Cu and 50 Co-50 Cu before and after annealing were investigated. In the as-sputtered state the films exhibit the structure of a metastable fcc solid solution. Annealing at 500 to 700°C causes decomposition into two phases, Cu and fcc 89 Co-11 Cu. The decomposition supposedly occurs by heterogeneous nucleation at the grain boundaries, and growth by grain boundary diffusion. The 89 Co-11 Cu phase exists in the form of small particles with magnetic single domain behavior. The films have coercivities up to 280 Oe. Squareness ratios between 0.7 and 0.9 were found. No strain sensitivity of the magnetic properties could be detected. This material is regarded to be suitable for magnetic recording.     

The magnetic properties of glass-ceramics in the CoO-Fe2O3-B2O3 system

The preparation of glasses in the CoO-Fe₂O₃-B₂O₃ system is described and it is shown that the magnetic spinel cobalt ferrite (CoFe₂O₄) can be obtained in precipitate when the glasses are heat-treated. The identity of the crystalline phase is established by means of Mössbauer spectroscopy. It is shown that the magnetic properties of the glass-ceramics can be controlled by means of the heat-treatment schedule and intrinsic coercivities as high as 1900 Oe are recorded. The magnetic properties of the as-cast and heat-treated material are discussed generally in terms of superparamagnetic, single domain and multi-domain behaviour. The highest values of the intrinsic coercivity and remanence are compared to those calculated for an assembly of non-interacting single domain particles with positive cubic magnetocrystalline anisotropy.     

Differential transformer cores for ground fault interrupting circuit breakers

The magnetic requirements of differential transformers used in ground fault interrupters (GFI) for the sensing of 5 mA ground faults over the temperature range from -35°C to +66°C have been established. Ring laminations made of vacuum-melted permalloy and annealed so that the magnetocrystalline anisotropyK_{1} sim 0just above the maximum operating temperature meet these requirements. Such heat treatment will produce rings with low remanence in which the low-flux-density permeability is stable with temperature and changes little from the demagnetized to the remanent state. The processing of rings and the influence of impurities are briefly discussed.