Applications of Electron Microscopy in Collaborative Industrial Research
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MRS BULLETIN/MAY 1996
sider collaborations with institutes such as NCEM. We have chosen three very different materials systems from a wide variety of projects in progress. In the first section, we describe a recent example where highresolution TEM has provided a clear picture of the microstructure of magnetic multilayers grown by molecular-beam
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Au spacer layer thickness (nm)
Figure 1. Oscillatory behavior of the magnetoresistance (AR/RJ as a function of the Au layer thickness. Data is shown for Py/Au and Pya6Au14/Au (where Py is permalloy, a Ni-Fe alloy) multilayers grown with (111)tcc epitaxy on a 2-nm Pt (111) buffer layer on a sapphire substrate.
epitaxy (MBE) at IBM's Almaden Research Center, enabling the magnetic properties of permalloy/gold multilayers to be correlated with the atomic-level structure. In the second section, we describe a study of the layered material SrBi2Ta2O9, which is of interest to Symetrix Corporation because of its applications in ferroelectric memory elements. Analytical and high-resolution microscopy were used to determine the phases present and to characterize the film quality, and the results were used to modify the device-processing conditions. Finally we describe research from Xerox Corporation on epitaxy in the GaN system, which has applications in blue light-emitting devices. In this project, the atomic arrangement at the interfaces between Al T Gai-,N epilayers and SiC and sapphire substrates was examined.
The Correlation Between Giant Magnetoresistance and Interface Structure in Magnetic Multilayers The discovery of giant magnetoresistance (GMR) in 19881*2 opened up a new chapter in the field of magnetism and magnetic materials. The origin of the effect is believed to be interfacial spindependent scattering of electrons as they traverse a thin nonmagnetic layer sandwiched between two magnetic layers. This scattering, and hence the magnetoresistance, is enhanced when the magnetization of adjacent magnetic layers is in opposite directions (antiferromagnetic [AF] coupling) and minimized when the magnetizations are in the same direction. Oscillations in both magnetoresistance and interlayer exchange coupling were found to be common to multilayers containing a variety of 3d transition and noble-metal spacer layers.3'4 This suggested the possibility of tailoring magnetic multilayers to achieve useful properties. For field-sensing applications, for example in magnetic read heads, it is essential to have GMR response in fields of only a few Oe. This requires that interlayer AF exchange-coupling fields be very weak so that they can easily be overcome by the external field to be sensed. Such a response can be achieved in multilayers made of permalloy (Py, a Ni-Fe alloy with -80% Ni) alternating with Au spacer layers.5 Figure 1 shows the variation of magnetoresistance with the Au spacer thickness for a Py/Au multilayer grown by MBE on a sapphire substrate. At each of the four maxima of magnetoresistance, AF coupling
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