Magnetic microscopy

H.Hopster, H.P.Oepen, Magnetic Microscopy of Nanostructures (Springer, Berlin, 2005). 

Rombaoh K, Laukemper-Ostendorf and Blumler P 1998 Applioations of NMR flow imaging in materials soienoe Spatially Resolved Magnetic Resonance, Proc. 4th Int. Cent, on Magnetic Resonance Microscopy and Macroscopy ed P Blumler, B Blumioh, R E Botto and E Fukushima (Weinheim Wiley-VCFI) pp 517-29... 

Biumioh B and Kuhn W (eds) 1992 Magnetic Resonance Microscopy Methods and Applications in Materials Science, Agriouiture and Biomedioine (Weinheim Wiiey-VCFI)... 

Biumier P, Biumioh B, Botto R E and Fukushima E (eds) 1998 Spatially Resolved Magnetic Resonance, Pros. 4th int. Conf. on Magnetio Resonance Microscopy and Macroscopy Ne nUe m Wiiey-VCFI)... 

These two references give an excellent overview over the most recent examples in this research field. Callaghan P T 1993 Principles of Nuclear Magnetic Resonance Microscopy (Oxford Clarendon)... 

Figure Bl.19.22. Magnetic force microscopy image of an 8 pm wide track on a magnetic disk. The bit transitions are spaced every 2 pm along the track. Arrows point to the edges of the DC-erased region. (Taken from [109], figure 7.)...

Kent A D, Shaw T M, Moinar S V and Awschaiom D D 1993 Growth of high aspect ratio nanometer-scaie magnets with chemicai vapor deposition and scanning tunneiiing microscopy Science 262 1249... 

Flobbs P, Abraham D and Wickramasinghe FI 1989 Magnetic force microscopy with 25 nm resolution Appl. Phys. Lett 55 2357... 

Rugar D, Mamin FI J, Guenther P, Lambert S E, Stern J E, McFadyen I and Yogi T 1990 Magnetic force microscopy general principles and application to longitudinal recording media J. Appl. Phys. 68 1169... 

For bulk structural detemiination (see chapter B 1.9). the main teclmique used has been x-ray diffraction (XRD). Several other teclmiques are also available for more specialized applications, including electron diffraction (ED) for thin film structures and gas-phase molecules neutron diffraction (ND) and nuclear magnetic resonance (NMR) for magnetic studies (see chapter B1.12 and chapter B1.13) x-ray absorption fine structure (XAFS) for local structures in small or unstable samples and other spectroscopies to examine local structures in molecules. Electron microscopy also plays an important role, primarily tlirough unaging (see chapter B1.17). 

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

Particles can be manipulated in suspension using strongly focused laser beams ( optical tweezers ) [25] or magnetic fields [26] and by collecting statistics on tire particle movements using video microscopy, infonnation on the particle interactions can be obtained. 

A variety of experimental techniques have been employed to research the material of this chapter, many of which we shall not even mention. For example, pressure as well as temperature has been used as an experimental variable to study volume effects. Dielectric constants, indices of refraction, and nuclear magnetic resonsance (NMR) spectra are used, as well as mechanical relaxations, to monitor the onset of the glassy state. X-ray, electron, and neutron diffraction are used to elucidate structure along with electron microscopy. It would take us too far afield to trace all these different techniques and the results obtained from each, so we restrict ourselves to discussing only a few types of experimental data. Our failure to mention all sources of data does not imply that these other techniques have not been employed to good advantage in the study of the topics contained herein. 

Several striking examples demonstrating the atomically precise control exercised by the STM have been reported. A "quantum corral" of Fe atoms has been fabricated by placing 48 atoms in a circle on a flat Cu(lll) surface at 4K (Fig. 4) (94). Both STM (under ultrahigh vacuum) and atomic force microscopy (AFM, under ambient conditions) have been employed to fabricate nanoscale magnetic mounds of Fe, Co, Ni, and CoCr on metal and insulator substrates (95). The AFM has also been used to deposit organic material, such as octadecanethiol onto the surface of mica (96). New appHcations of this type of nanofabrication ate being reported at an ever-faster rate (97—99). 

The mechanism for coercivity in the Cr—Co—Fe alloys appears to be pinning of domain walls. The magnetic domains extend through particles of both phases. The evidence from transmission electron microscopy studies and measurement of JT, and anisotropy vs T is that the walls are trapped locally by fluctuations in saturation magnetization. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

A detailed account is given in Reference 20. The techniques giving the most detailed 3-D stmctural information are x-ray and neutron diffraction, electron diffraction and microscopy (qv), and nuclear magnetic resonance spectroscopy (nmr) (see Analytical methods Magnetic spin resonance X-ray technology). 

Alternatives to XRD include transmission electron microscopy (TEM) and diffraction, Low-Energy and Reflection High-Energy Electron Diffraction (LEED and RHEED), extended X-ray Absorption Fine Structure (EXAFS), and neutron diffraction. LEED and RHEED are limited to surfaces and do not probe the bulk of thin films. The elemental sensitivity in neutron diffraction is quite different from XRD, but neutron sources are much weaker than X-ray sources. Neutrons are, however, sensitive to magnetic moments. If adequately large specimens are available, neutron diffraction is a good alternative for low-Z materials and for materials where the magnetic structure is of interest. 

---