Magnetic force microscopy: General principles and application to longitudinal recording media

Abstract

This paper discusses the principles of magnetic force microscopy (MFM) and its application to magnetic recording studies. We use the ac detection method which senses the force gradient acting on a small magnetic tip due to fields emanating from the domain structure in the sample. Tip fabrication procedures are described for two types of magnetic tips: etched tungsten wires with a sputter-deposited magnetic coating and etched nickel wires. The etched nickel wires are shown to have an apex radius on the order of 30 nm and a taper half-angle of approximately 3°. Lorentz-mode transmission electron microscopy of the nickel tips reveals that the final 20 μm is essentially single domain with magnetization approximately parallel with the tip axis. Images of written bit transitions are presented for several types of magnetic media, including CoPtCr, CoSm, and CoCr thin films, as well as γ-Fe2O3 particulate media. In general, the written magnetization patterns are seen with high contrast and with resolution better than 100 nm. A number of magnetic recording applications are discussed, including the investigation of overwrite behavior and the writing characteristics in CoSm media at high data density. Computer calculations were performed to simulate the MFM response to written magnetic transitions. By including the extended geometry of the tip, the nonparallel orientation of the cantilever, and the finite width of the magnetic transitions, good agreement with experiment was obtained. The model calculations correctly predict the experimentally observed change in image contrast that occurs as a function of tip orientation. Computer calculations showing the dependence of resolution on tip geometry are also presented.

The importance of cantilever dynamics in the interpretation of Kelvin probe force microscopy

“…Our analysis here has centered around amplitude modulated KPFM, but these findings and methods are relevant to any AFM technique that uses a long-range interaction, including other types of EFM and Magnetic Force Microscopy. 29 FIG. 5.…”

Magnetic, morphological and structural investigations of CoFe/Si interfacial structures

“…The shift in resonant frequency is proportional to @F z @Z ; with F z being the component of force acting along z-direction on the tip by field of the sample. [26] This change in resonant frequency causes phase lag ðDf ¼ Q K 0 ÁF 0 Þ in cantilever's oscillation, which is measured by the optical interferometry technique and forms the image as bright (i.e. @F z @Z < 0, þve phase shift) and dark (i.e.…”

“…[26] Due to the presence of tip-sample interaction, the cantilever behaves as it had modified spring constant K, according to the relation: K ¼ K 0 þ F 0 , where K 0 is a natural spring constant and F 0 @F z @Z is the derivative of interaction force gradient along z-axis.…”

Fabrication and characterization of high aspect ratio perpendicular patterned information storage media in an Al2O3/GaAs substrate

“…8 we use a home made MFM utilizing electrochemically etched nickel tips 9 and a fiber-optic interferometer 10 as the vibration detector. We focused our investigation on the corner pattern of one of the fabricated arrays in order to compare images from the same columns obtained through the two measurement techniques.…”