Low-noise magnetic force microscopy with high resolution by tip cooling

Low-noise magnetic force microscopy (MFM) was realized by using a conventional high-vacuum MFM with homemade tip-cooling equipment. The noise level of the MFM at a tip temperature of 130 K was estimated at /spl mu/N/m order. High spatial resolution of 10 nm was obtained for observing high-density recording media with recording density of 1000 kfci. The improvement of resolution by tip cooling was a result of the reduction of thermodynamic noise of a cantilever and the effective reduction of tip-sample distance due to the magnetic hardening of a tip.     

Effect of induced shape anisotropy on magnetic properties of ferromagnetic cobalt nanocubes

We report on the synthesis of ferromagnetic cobalt nanocubes of various sizes using thermal pyrolysis method and the effect of shape anisotropy on the static and dynamic magnetic properties were studied. Shape anisotropy of approximately 10% was introduced in nanocubes by making nanodiscs using a linear chain amine surfactant during synthesis process. It has been observed that, ferromagnetism persisted above room temperature and a sharp drop in magnetic moment at low temperatures in zero-field cooled magnetization may be associated with the spin disorder due to the effective anisotropy present in the system. Dynamic magnetic properties were studied using RF transverse susceptibility measurements at different temperatures and the singularities due to anisotropy fields were probed at low temperatures. Symmetrically located broad peaks are observed in the frozen state at the effective anisotropy fields and the peak structure is strongly affected by shape anisotropy and temperature. Irrespective of size the shape anisotropy gave rise to higher coercive fields and larger transverse susceptibility ratio at all temperatures. The role of shape anisotropy and the size of the particles on the observed magnetic behaviour were discussed.     

Tunneling-stabilized magnetic force microscopy of bit tracks on ahard disk

A scanning tunneling microscope (STM) for surface magnetic force measurements on thin-film longitudinal magnetic storage media is described. The usual rigid PtIr tip of the STM was replaced by a flexible Fe-film tip and the tip position was stabilized near the surface of the sample using the STM feedback system as tunneling occurs between the tip and sample surface. Images of a CoCrTa thin-film hard disk showing 5 μm×3 μm bit tracks written by the ferrite head of a computer disk drive are presented. The images shown are comparable to images of the bit tracks on textured surfaces using either ferrofluid decoration or other magnetic force microscopy (MFM) imaging techniques. The sensitivity of the Fe-film tip was such that the influence on the image due to magnetic forces was larger than the influence due to sample surface topography     

A high performance lipase preparation: characterization and atomic force microscopy

The goal of obtaining enzyme forms which show greater stability, higher catalytic efficiency, and reusability has been pursued since last several decades. Some novel biocatalyst designs have been evolved and protein coated micro-crystals (PCMCs) is one of them. Pseudomonas cepacia lipase coated micro-crystals were prepared by simultaneous precipitation of mixture of aqueous lipase solution and salts such as potassium sulphate by organic solvents. This resulted in lipase coated micro-crystals. The structures of micro-crystals were studied by atomic force microscopy (AFM). The AFM picture confirmed the enzyme coating over the potassium sulphate crystals. These PCMCs are in the size range of 500-1000 nm. These enzyme coated micro-crystals showed enhanced transesterification rates. Also, the PCMC were stable at 60 degrees C whereas the free enzyme lost all its activity. The enzyme coated micro-crystals prepared by 50 mg Pseudomonas cepacia lipase gave 96% conversion in 90 min whereas free enzyme gave 8% conversion. Even PCMCs prepared from 3.12 mg lipase gave 90% conversion in 10 h at 60 degrees C where as free lipase was inactive at 60 degrees C.     

Thermomagnetic fluctuations and hysteresis loops of magnetic cantilevers for magnetic resonance force microscopy

We have used frequency-shift cantilever magnetometry to study individual nickel magnets patterned at the end of ultra-sensitive silicon cantilevers for use in magnetic resonance force microscopy (MRFM). We present a procedure for inferring a magnet's full hysteresis curve from the response of cantilever resonance frequency versus magnetic field. Hysteresis loops and small-angle fluctuations were determined at 4.2 K with an applied magnetic field up to 6 T for magnets covering a range of dimensions and aspect ratios. Compared to magnetic materials with higher anisotropy, we find that nickel is preferable for MRFM experiments on nuclear spins at high magnetic fields.     

Shear-mode magnetic force microscopy with a quartz tuning fork in ambient conditions

We have demonstrated high-resolution shear-mode magnetic force microscopy (MFM) using a quartz tuning fork in ambient conditions. A commercial magnetic cantilever tip was attached to one prong of the tuning fork to realize shear-mode MFM operation. We have obtained MFM images with a spatial resolution of less than 100?nm and demonstrated a frequency resolution of ～1?mHz, values which are achieved by phase shift detection methods.     

3D physical modeling of anisotropic grain growth at high temperature in local strong magnetic force field

A new mechanism based on the effect of local magnetic forces on diffusing ions around a growing ferromagnetic precipitate is proposed. A 3D simulation based only on physical parameters is undertaken in which main assumption is of interface limited growth controlled by the effect of both curvature and local magnetic field distortion. Although usually neglected in magnetic field effect mechanisms, it is shown that these local magnetic forces acting on a single paramagnetic ion can change markedly affect the growth process and induce strong shape anisotropy.     

3D physical modeling of anisotropic grain growth at high temperature in local strong magnetic force field

Abstract

A new mechanism based on the effect of local magnetic forces on diffusing ions around a growing ferromagnetic precipitate is proposed. A 3D simulation based only on physical parameters is undertaken in which main assumption is of interface limited growth controlled by the effect of both curvature and local magnetic field distortion. Although usually neglected in magnetic field effect mechanisms, it is shown that these local magnetic forces acting on a single paramagnetic ion can change markedly affect the growth process and induce strong shape anisotropy.     

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.     

Multimodal atomic force microscopy: Biological imaging using atomic force microscopy combined with light fluorescence and confocal microscopies and electrophysiologic recording

Because the atomic force microscope (AFM) allows molecular resolution imaging of hydrated specimens, it provides a unique window to the microscopic biological world. A high signal-to-noise ratio in AFM images sets them apart from the images obtained from other techniques: One does not need extensive image analyses often required by other techniques to obtain high-resolution information. AFM can provide molecular details on crystalline as well as amorphous materials. However, it is often limited in providing identity of the imaged structures, especially in a complex system such as a cellular membrane. AFM's application for biological imaging will rely on an unambiguous identification of imaged structures. For mixed macromolecules, it may be essential to make critical comparisons of the same structural features imaged with AFM and other techniques such as light fluorescence and confocal microscopies, electron microscopy and X-ray diffraction, and biochemical, immunologic, and pharmacologic techniques and electrophysiologic recordings. Significantly, the simple design of AFM allows it to be integrated with other techniques for simultaneous multimodal imaging. Recent combined multimodal imaging include light fluorescence, confocal, and near-field optical imaging as well as electrophysiologic recordings. Preliminary studies from such multimodal imaging include 1) an independent identification of macromolecules in a complex specimen using appropriately labeled markers such as fluorescent-dye labeled antibodies or dark-field microscopy; 2) imaging real-time reorganization of surface features using laser confocal and AFM; 3) a direct correlation of structural features and ion transfer via pores in a membrane; and 4) macromolecular complexes such as receptor-ligand and antigen-antibody. These features of a multimodal imaging system will provide new and significant avenues for a direct real-time structure-function correlation studies of biological macromolecules. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 293–300, 1997     

具有磁性涂层的连续碳纤维基本磁特性研究及其各向异性计算

具有磁性涂层的连续碳纤维其基本磁参数可以通过振动样品磁强计的测试(VSM)来表征,经理论推算和实验测量,论证了该方法的合理性.同时应用该方法检测了连续纤维的矫顽力(Hc)和比饱和磁化强度(σs),并由此对其各向异性进行理论计算,计算结果与纤维磁性涂层形状各向异性相吻合.     

Extremely high dose neutron dosimetry using CR-39 and atomic force microscopy

Atomic force microscopy (AFM) has been applied to the analysis of CR-39 nuclear track detectors for high dose neutron dosimetry. As a feasible study to extract the neutron dose, we have employed a (239)Pu-Be neutron source with the traditional track density measurement of recoil proton etch pits from a high density polyethylene (CH(2)) radiator. After very short etching ( approximately 1 microm), etch pit densities were measured as a function of neutron fluence (neutron dose) up to 1.4 x 10(10) cm(-2) (6.6 Sv). Neutron sensitivity was also measured to be 6.6 x 10(-4). Maximum measurable neutron dose was estimated to be approximately 200 Sv by measuring the fraction of the total image area occupied by the etch pits.     

强磁场对聚苯胺颗粒结构的取向性研究

聚苯胺颗粒结构对其电学、光学性能有很大的影响。本文首次在10T强磁场的作用下用化学氧化溶液原位聚合法得到聚苯胺并观察充分聚合后聚苯胺的颗粒结构、形貌牲。强磁场作用下的原位聚合聚苯胺颗粒呈现大约50nm的棒状,而对本征态聚苯胺在强磁场下再掺杂得到20～30nm的球状颗粒,与未加强磁场作用下的礁石状颗粒有明显区别。分析认为这是由于强磁场对聚苯胺晶粒的取向作用所至。     

Transition-metal dimers and physical limits on magnetic anisotropy

Recent advances in nanoscience have raised interest in the minimum bit size required for classical information storage. This bit size is determined by the necessity for bistability with suppressed quantum tunnelling and energy barriers that exceed ambient temperatures. In the case of magnetic information storage, much attention has centred on molecular magnets with bits consisting of about 100 atoms, magnetic uniaxial anisotropy energy barriers of about 50 K and very slow relaxation at low temperatures. Here, we draw attention to the remarkable magnetic properties of some transition-metal dimers, which have energy barriers approaching 500 K with only two atoms. The spin dynamics of these ultrasmall nanomagnets is strongly affected by a Berry phase, which arises from quasi-degeneracies at the electronic highest occupied molecular orbital energy. In a giant-spin approximation, this Berry phase makes the effective reversal barrier thicker.     

Permanent magnets based on materials with high crystal anisotropy

The properties of Alnicos and elongated single-domain fine-particle materials, both interpreted as due to shape anisotropy of fine particles, are still far short of those predicted by simple theory. The hard ferrites, with properties due to magnetocrystalline anisotropy, come much closer, but are restricted by their low magnetization. The search for a combination of high magnetization and high magnetocrystalline anisotropy has led to the investigation of a variety of intermetallic compounds. Some of them, particularly the cobalt-rare earths, appear quite promising. Mechanical grinding often has an adverse effect on the magnetic properties of crystal anisotropy materials. Chemical stability is also often a problem. Crystal anisotropy materials in general have high values of intrinsic coercive force. This makes them especially suitable for applications involving widely varying dynamic conditions. Their proper evaluation may be best done using criteria other than the usual maximum energy product.