Nanoscale Magnetic Characterization
An elusive goal in the studies of different phenomena in a wide variety of magnetic nanostructures and nanosystems is the observation of very weak magnetic fields with atomic resolution. To map magnetic fields directly and non-invasively, we use Scanning Hall Probe Microscopy, a quantitative technique that allows one to register minute magnetic fields from a sample with high spatial resolution. Scanning Hall Probe Microscope (SHPM) developed by the team members from NanoMagnetics Instruments is capable of performing both high-resolution imaging and spectroscopy (presently with 120nm spatial and with magnetic field sensitivity ~3.3 nT/√Hz at 4.2K). SHPM has a number of important advantages compared to other magnetic probes:
  • It is non-invasive, as the probe is non-magnetic and thus does not disturb the system under study.
  • It measures magnetic field directly rather than field derivatives (as in MFM).
  • Its sensitivity at low temperatures is already compatible to the best micro-SQUIDs.
  • It has scanning capabilities and (in contrast to a micro-SQUID) can operate in large external magnetic fields.
A detailed description of the SHPM and examples of scans taken at different temperatures are given in Techniques. Several images of magnetic systems obtained at WSU during the microscope testing and calibration are shown below.

Fig. 1 - Left panel: Room temperature "magnetograph" of magnetic domains and domain walls in an NdFeB bulk sample. The sample is scanned in a contact mode (provided by the STM feedback), providing a fairly good spatial resolution of the large magnetic fields on the surface (of the order of 2-3kGs). The scan size is 56µmx56µm. Below: A 3D representation of the magnetic image. Right panel: Surface morphology the same sample obtained with Scanning Tunneling Microscope in the same scan.

Fig. 2 - A magnetic image of a commercial hard drive obtained with the SHPM.

Copyright ©2006 Boris Edward Nadgorny