PALEOMAGNETISM AND GEOPHYSICS

Reading the record one grain at a time

Natural magnetic minerals lock in the Earth's magnetic field as they form, but not every grain is a dependable recorder. Whether a grain holds a stable remanence depends on its internal domain state, and that is a property of the individual particle. Bulk magnetometry averages over millions of them at once.


The QSM measures the stray magnetic field above a single grain, quantitatively and at 30 nm spatial resolution. Instead of inferring what a population is doing, you see what one particle is doing.


Get in touch to discuss your samples, whether they are FIB-prepared grains, polished sections or loose powder.

1 µm magnetite grain scans

A pure magnetite grain of roughly 1 µm was isolated from a natural sample by focused ion beam milling, then magnetised along one cube axis at approximately 700 mT. The stray field was mapped by QSM at a stand-off of 300 nm above the sample surface, at 30 nm resolution. The grain was then re-magnetised at 150 mT along the X and Z directions, with a full field map acquired after each step.


Stray fields of order 10 mT were resolved above the grain. Each magnetisation history produced a distinctly different field pattern, consistent with multi-domain behaviour rather than a single uniform moment. This is the level of detail that separates a grain carrying an interpretable remanence from one that does not.

After 700 mT
After 700 mT
NV scan of the grain after being magnetized to 700 mT along the vertical axis, B pointing down.
After 150 mT
After 150 mT
NV scan of the grain after being magnetized to 150 mT with the QZabre vectormagnet along the horizontal axis, B pointing to the left.
After 150 mT
After 150 mT
NV scan of the grain after being magnetized to 150 mT with the QZabre vectormagnet along the in plane axis, B pointing inwards.

How to measure a single grain?

Sub-micron domain structure is beyond the reach of bulk and widefield methods, grains sit sparsely in a non-magnetic matrix, and contrast-only techniques such as MFM cannot be inverted to a magnetisation. Scanning NV magnetometry addresses all three. The NV center in a QZabre scanning tip is an atomic-sized sensor with a calibrated response, so the output is a magnetic field in physical units, ready for dipole fitting, moment reconstruction or micromagnetic tomography with no separate calibration step.


  • 30 nm spatial resolution, set by the sensor-sample distance rather than a diffraction limit
  • Quickscan and the NV Advanced Modes Extension locate sparse grains over large areas at up to 200 pixels/s, so high-resolution scans follow only on the grains that matter
  • Correlated topography, since the QSM is an AFM: the field map is registered to the grain and the stand-off distance is known (Xu et al., ACS Nano 2025)
  • Room temperature and ambient, no cryogenics or vacuum, so the same grain can be removed, treated and scanned again
  • Powders and dispersed grains work as well as FIB-prepared single grains, provided the grains are immobilised and the scan surface is reasonably flat. Embedded in resin and polished, dispersed on a flat substrate, or held under a thin capping layer are all suitable. Particles in a dispersion are resolved separately within one scan, mapping a size and shape distribution onto a distribution of magnetic states


Send us a description of your sample and we will tell you what preparation is needed.

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QSM microscope