Figure 1

How an MRFM works -- The magnetic resonance force microscope (MRFM) uses an ultra-thin silicon cantilever (yellow) with a nanometre size magnetic tip (blue) to detect the magnetic signal from an individual electron buried below the surface of the sample. Because the electron has a quantum mechanical property called spin, it acts like a tiny bar magnet and can either attract or repel the magnetic tip. The interaction between the spin and the tip is confined to the bowl-shaped region in the sample called the "resonant slice", which moves as the cantilever vibrates. With the aid of a high-frequency magnetic field generated by a coil (right, background), the orientation of the electron (green arrow) flips as the resonant slice passes through. The magnetic force between the electron and magnetic tip alternates between attraction and repulsion every time the electron flips its orientation, causing the cantilever frequency to change slightly. A laser beam (left) is used to precisely measure the variations in cantilever vibration frequency (image credit: D Rugar IBM 2004).

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