magnetic force

Attraction or repulsion that arises between electrically charged particles that are in motion. While only electric forces exist among stationary electric charges, both electric and magnetic forces exist among moving electric charges. The magnetic force between two moving charges is the force exerted on one charge by a magnetic field created by the other. This force is zero if the second charge is traveling in the direction of the magnetic field due to the first and is greatest if it travels at right angles to the magnetic field. Magnetic force is responsible for the action of electric motors and the attraction between magnets and iron.

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An atomic force microscopy (AFM). Unlike typical AFM, magnetic materials are used for the sample and tip, so that not only the atomic force but also the magnetic interaction are detected. Many kinds of magnetic interactions are measured by MFM, including magnetic dipolar interaction. MFM scanning often uses non-contact AFM (NC-AFM).

In MFM measurements, the magnetic force between the sample and tip is given by:

F = (m .∇)H

m: magnetic moment of the tip

H: magnetic stray field from the sample

Because the magnetic stray field from the sample will affect the magnetized state and vice versa, in most cases it is difficult to obtain quantitative information from the MFM measurement. To interpret the information quantitatively, the configuration of the tip must be known. With this measurement, a typical resolution of 30 nm can be achieved (Abelmann, 1998). Although resolutions as high as 10 nm are attainable (Nanoscan AG, February 2008).

A potential method of increasing the resolution would involve using an electromagnet on the tip instead of a permanent magnet. Enabling the magnetic tip only when placed over the pixel being sampled could increase the resolution.

References

• L. Abelmann, S. Porthun, M. A. M. Haast, J. C. Lodder, A. Moser, M. E. Best, P. J. A. Schendel, B. Stiefel, H. J. Hug, G. P. Heydon, A. Farley, S. R. Hoon, T. Pfaffelhuber, R. Proksch, K. Babcock (1998). "Comparing the resolution ofƏÊ magnetic force microscopes using the CAMST reference samples". J Magn Magn Mater 190 135–147.
• Nanoscan AG Quantum leap in hard disk technology. .