Abstract
Sensitive detection of weak magnetic moments is an essential capability in many areas of nanoscale science and technology, including nanomagnetism, quantum readout of spins and nanoscale magnetic resonance imaging. Here we show that the write head of a commercial hard drive may enable significant advances in nanoscale spin detection. By approaching a sharp diamond tip to within 5 nm from a write pole and measuring the induced diamagnetic moment with a nanomechanical force transducer, we demonstrate a spin sensitivity of 0.032 μB Hz−1/2, equivalent to 21 proton magnetic moments. The high sensitivity is enabled in part by the pole's strong magnetic gradient of up to 28 × 106 T m−1 and in part by the absence of non-contact friction due to the extremely flat writer surface. In addition, we demonstrate quantitative imaging of the pole field with ∼10 nm spatial resolution. We foresee diverse applications for write heads in experimental condensed matter physics, especially in spintronics, ultrafast spin manipulation and mesoscopic physics.
Highlights
Sensitive detection of weak magnetic moments is an essential capability in many areas of nanoscale science and technology, including nanomagnetism, quantum readout of spins and nanoscale magnetic resonance imaging
We introduce a variant of force microscopy—magnetic susceptibility force microscopy—to localize and measure the write pole field quantitatively and with high spatial resolution
For a point-like particle located at position r, the force is where l 1⁄4 VM 1⁄4 VwB/m0 is the magnetic moment and V the volume of the particle
Summary
Sensitive detection of weak magnetic moments is an essential capability in many areas of nanoscale science and technology, including nanomagnetism, quantum readout of spins and nanoscale magnetic resonance imaging. By approaching a sharp diamond tip to within 5 nm from a write pole and measuring the induced diamagnetic moment with a nanomechanical force transducer, we demonstrate a spin sensitivity of 0.032 mB Hz À 1/2, equivalent to 21 proton magnetic moments. Write fields must be confined to a very narrow region in space, leading to extremely high local gradients These gradients cannot be precisely measured, they are estimated to exceed 20 Â 106 T m À 1 Write poles are rapidly switchable, potentially allowing for dynamical control of magnetic fields up to 1 GHz (refs 5,6) at low power consumption With these features, the hard drive industry has created a tool that could enable important advances in many areas of nanoscale experimental physics. Our method provides advantages over magnetic force microscopy (MFM)[13,14,15,16,17] and electron holography[18], which are difficult to quantify, barely reach sufficient resolution, or provide two-dimensional projections
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