Magnetic Force Microscopy: Recent Advances and Applications
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ABSTRACT We review the principles of magnetic force microscopy and describe recent advances in imaging methods and probes. Some current applications of MFM in experimental micromag-
netism and materials development are also discussed, as well as challenges in image interpretation and in using MFM for quantitative work.
INTRODUCTION Magnetic force microscopy (MFM) has emerged as a powerful tool for mapping surface magnetic
fields. The basic capabilities of MFM include resolution on a 10 nm scale, sensitivity ample to image single submicron particles, imaging through opaque and nonmagnetic overlayers, and operation in ambient conditions with minimal sample preparation.Y"3 These have made MFM an appealing alternative to conventional magnetic imaging methods (eg., Kerr microscopy and Lorenz TEM) since its inceptionI as an offshoot of scanning probe microscopy (SPM). Early MFMs were cumbersome and difficult to use for all but SPM experts, and MFM did not spread widely at first. Recent advances in batch-fabrication of scanning probes4'5 and improved methods for acquisition of topographical and magnetic data have increased reliability and ease-of-use. The appearance of commercial instruments has made MFM feasible for a wide range of users, and there has been rapid growth in MFM applications in materials science and data storage. 6 Some current work still focuses on aspects of MFM itself, particularly probes and quantitative analysis, and in specialty areas such as low temperature imaging.' There is,nonetheless, an ongoing shift in the scientific literature from papers demonstrating particular MFM capabilities to those which present new results obtained by MFM. In this paper we review the principles of MFM required to produce images such as Fig. 1. We
also describe a widely-used technique for imaging surface topography with the full resolution of atomic force microscopy, while simultaneously acquiring magnetic data. Comparing both data types
gives valuable information about surface morphology and its effect on magnetic properties. In the course of this discussion we will describe some recent applications from materials science and data
storages. A few of these applications demonstrate the utility of MFM for experimental testing of Fig 1. Magnetic force gradient image of an experimental PrFeB-based permanent magnet material. As explained in the text, shifts in the 85 kHz cantilever resonant frequency were mapped with the tip lifted 30 nm above the surface. Lipht (dark) areas indicate positive (negative) frequency
shifts, with a range of 75 Hz for the image. The magnetition is in-plane except for the grain of pendicular serpentine domains Sample courtesy of Prof. R. Street, L. Folks, and R. Woodward, Dept. of Physics, University of Western Australia.
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20 gm 311 Mat. Res. Soc. Symp. Proc. Vol. 355 01995 Materials Research Society
micromagnetic theory, an area that has long lacked the necessary tools for experimental tests on relevant length scales. Others focus on the characterization of magnetic materials and rec
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