Direct measurement of internal magnetic fields in natural sands

Local changes in magnetic fields in porous media are important because they can influence measurements of the NMR relaxation parameters. Quantification of internal fields can be difficult by NMR alone. To unambiguously and directly quantify the spatial distribution of internal magnetic fields we employ scanning SQUID microscopy. We measured selected grains of a natural sand (obtained from the Ogallala aquifer) with grain sizes of about 200 μm, and detected relatively high internal magnetic fields (~ 1 mT) and gradients (> 5 T/m) in a very small background field (~ 2 μT).

Journal of Magnetic Resonance (2014)

With: Jan Walbrecker, Kathryn Moler, Rosemary Knight @ Stanford

Tuning the magnetism in LAO/STO

We are trying to learn more about the microscopic nature of this magnetism by tuning it in different ways. For example we found that local strain manipulates the ferromagnetic patches in LAO/STO. The images below show repeated scans of a small group of ferromagnetic patches that change as a result of local strain we apply with the tip of the SQUID’s chip.
Scanning Probe Manipulation of Magnetism at the LaAlO₃/SrTiO₃ Heterointerface
Nano Letters (2012)

With: Kathryn Moler, Harold Hwang