The high spatial resolution imaging of magnetic microstructure has important ramifications for both fundamental studies of magnetism and the technology surrounding the magnetic recording industry. One technique for imaging surface magnetic microstructure on the 10‐nm‐length scale is scanning electron microscopy with polarizationanalysis (SEMPA). This technique employs a scanning electron microscope(SEM) electron optical column to form a medium energy (10–50 keV), small probe ( 1 nA) on a ferromagnetic specimen. Secondary electrons excited in the ferromagnet by the high spatial resolution probe retain their spin‐polarization orientation as they leave the sample surface. The spin polarization of the emitted secondary electrons can be related directly to the local magnetization orientation. A surfacemagnetization map is generated when the spin polarization of the secondary electrons is analyzed as the electron beam is rastered point‐by‐point across the ferromagnet’s surface. In this review article we review the important instrumental components characterizing the SEMPA system. Characteristics of the electron probe forming optics, electron spin‐polarization analyzers with associated transport optics, and signal processing electronics will be described. Emphasis on the fundamental design requirements will be stressed. Data acquisition, storage, and processing, as it applies specifically to SEMPA, will be reviewed. Instrumental artifacts specific to SEMPA will be outlined and techniques for their correction given. Examples of magnetic images at high spatial resolution will be shown.

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Scanning electron microscopy with polarization analysis (SEMPA)

Spin-polarized scanning electron microscopy (spin-SEM) is a magnetic domain observation method. In spin-SEM, polarization of secondary electrons emitted from a sample in a scanning electron microscope is detected by a spin detector and used as a signal for forming an image. The characteristics of spin-SEM are detection of all three magnetization vector components, which leads to the detection of the magnetization vector direction, high spatial resolution of around 3 nm and applicability to samples with rough or even 3D surfaces. Spin-SEM combined with other imaging methods using an electron probe beam such as scanning Auger electron microscopy for imaging element distribution and electron backscattering diffraction microscopy for imaging crystal direction distribution provides additional information that is important to study the magnetism. Spin-SEM with these excellent characteristics has a broad range of applications from basic research to applied research and developments in various industries.

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Spin-polarized scanning electron microscopy

We compare quantitative results from two methods of solving the micromagnetics equations for 180° domain walls. The first method solves the Landau–Lifshitz–Gilbert equation by time integration of the stiff differential equations. The second method uses a relaxation scheme to determine the equilibrium domain wall magnetization configuration. We compare results from these calculations for various damping parameters and discretization mesh densities, and also compare our results with domain wall measurements made using scanning electron microscopy with polarization analysis. We conclude that equilibrium domain wall microstructure is insensitive to the damping parameter used in the time method of solution for domain walls in magnetically soft iron and Permalloy. For large damping parameters, the approach to equilibrium is the same for the time method and the relaxation method. Further, we can obtain metastable equilibrium states with both methods.

Micromagnetic calculations of 180° surface domain walls

Electrodeposition processes have been extensively used in thin-film head fabrication. Extremely fine features can be produced using photolithographic pattern definition followed by electroplating. Permalloy has been exclusively used for the pole material. Some critical aspects, such as film composition, magnetostriction, and stress level, were found to have a significant effect on head performance. Attempts were made to produce single-domain pole structures by lamination to eliminate output instability caused by nonrepeatable domain wall motions. Alternative improvements were brought about by increasing H/sub k/ and thus reducing the size of the closure domains. Electroplated CoFe and CoFe ternary alloy thin films were found to have very high saturation magnetization ( approximately 1.9 T). The CoFe ternary alloy has rotatable anisotropy. Higher permeability can be obtained by electroplating under an alternatingly switched field. >

Electrodeposition of magnetic materials for thin-film heads

Using controlled N2/Ar sputtering gas mixtures, rf‐sputtered films were prepared from Fe, Ni, and Ni81Fe19 targets, and their structure and orientation were studied by x‐ray diffraction. When no N2 was introduced during sputtering, all the films were oriented in the highest density planes; i.e., in (110), (111), and (111) for α‐Fe, Ni, and γ‐Ni81Fe19, respectively. With increasing N2 introduction, however, the orientation shifted to lower density planes, and eventually nitrides were formed. Multilayer films of metal and nitride were prepared with the Ni81Fe19 target by repetitive supply of N2 for short periods during sputtering. Strong orientation effects were observed depending on the number of layers grown. In addition, the x‐ray diffraction of these films presented evidence of epitaxial growth of the nitrides (Ni,Fe)4N on the alloy layers.

Structure and orientation of films prepared by reactive sputtering of Ni, Fe, and NiFe in Ar/N2 mixtures

The domain structures of cores patterned in thin film heads for disk drive systems were investigated by using spin-polarized SEM. This method made it possible to determine the direction of the magnetization at the domains and domain walls in magnetic cores accurately. Domain structures in the track width, as small as 10 μ m could be observed. Domain structure could also be observed at the tapering area of a thin film head. It was found that the triangular domains without the closure domains are located at the edge of the magnetic core in single- and six-layered permalloy films in some cases. Such a domain structure was regarded as causing the wiggles in the read-out waveforms.

N. Narishige

Papers

Magnetic domains of permalloy films for magnetic recording thin film heads observed by spin-polarized SEM