Nuclear resonance scattering

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Nuclear resonance scattering or NRS is a technique that is related to Mössbauer spectroscopy. With monochromatic synchrotron radiation pulses, spaced a few 100 ns apart, a nucleus is excited to a higher nuclear state. When the nucleus de-excites again, due to the splitting of the nuclear states into hyperfinelevels 1-100 neV apart, this de-excitation will be separated in time. The intensity of the measured radiation due to the delayed de-excitation is then accumulated over time. This so-called time spectrum, when Fouriertransformed, gives information about the frequencies involved, making determining characteristics of the hyperfine field, quadrupole splitting and isomer shift possible.
The technique is particularly sensitive to the oriëntation of the magnetisation relative to the direction of the incoming beam. when parallel to each other, the time spectrum only consists of one frequency, becoming more complex if the hyperfine field and beam direction are oriënted differently.

Example:
It is possible with this technique to measure the oriëntation of the magnetisation in materials like Fe over time. When deposing a thin film onto a clean substrate, with nuclear resonance scattering, the oriëntation of the Bhf of iron can be studied in function of the incident beam direction and the deposition time required to form the layer. By comparing the time spectrum of the material for different directions of the incident beam, the direction of the magnetisation can be reconstructed for every layer of the sample. It is with this technique that for the first time a spintransition from out to in plane was directly detected at room temperature. Before this, a spintransition was only measured at low K in the first surface layers of the sample with the help of spin polarised scanning tunneling electron microscopy (SP-STM).

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