Magnetic states can be read out using short current pulses. Ultra-short terahertz light pulses are also capable of doing this and will probably also be able to write them in the future.
Researchers at the Helmholtz-Zentrum Dresden-Rossendorf used the ELBE radiation source as a light source. The samples investigated consisted of at least two extremely thin, superimposed layers. For the bottom layer, the researchers chose a magnetic material, for example from the element cobalt or from an iron-nickel alloy. The upper layer consisted of metals such as platinum, tantalum or tungsten. None of these metallic layers was thicker than three nanometres so that the material could be penetrated by part of the terahertz radiation and the magnetization could be read out. After penetrating the sample, a harmonic (the so-called "second harmonic") with twice the frequency of the original terahertz radiation is obtained. This harmonic can be detected and thus the magnetization of the lower layer can be determined within picoseconds.
