Washington, March 31 : Researchers have succeeded, for the first time, in a direct, three-dimensional visualisation of magnetic fields inside solid, non-transparent materials.
Nikolay Kardjilov and colleagues from the Hahn-Meitner-Institute (HMI), in cooperation with University of Applied Sciences in Berlin, conducted the research.
The researchers in the imaging group used neutrons, subatomic particles that have zero net charge, but do have a magnetic moment, making them ideal for investigating magnetic phenomena in magnetic materials.
When in an external magnetic field, the neutrons behave like compass needles, all aligning to point on the direction of the field.
Neutrons also have an internal angular momentum, often referred to by physicists as spin, a property that causes the needle to rotate around the magnetic field, similar to the way in which the Earth rotates on its axis.
When all of the magnetic moments point in the same direction, then the neutrons are said to be spin-polarised. If a magnetic sample is irradiated with such neutrons, the magnetic moments of the neutrons will begin to rotate around the magnetic fields they encounter in the sample and the direction of their spin changes.
Kardjilov's group used this phenomenon as a measurement parameter for tomography experiments using two spin polarisers (which only allow the passage of neutrons whose spin points in a specific direction) to polarise and then analyse the neutrons.
By detecting changes in the spins, it is possible to "see" the magnetic fields within the sample.
According to Nikolay Kardjilov, "The equipment only allows passage of neutrons with a specific spin rotation, and this generates the contrast according to how the magnetic properties are distributed within the specimen. By rotating the specimen, we can reconstruct a three-dimensional image."
With Kardjilov's experimental setup, it is now possible, among other things, to visualise magnetic domains in magnetic crystals three-dimensionally.