- Ferromagnetic resonance
Ferromagnetic resonance, or FMR, is a
spectroscopic technique to probe themagnetization offerromagnetic materials. It is a standard tool for probingspin wave s and spin dynamics. It was unknowingly discovered by V. K. Arkad'yev when he observed the absorption of UHF radiation by ferromagnetic materials in 1911. A qualitative explanation of FMR along with an explanation of the results from Arkad'yev was offered up by Ya. G. Dorfman in 1923 when he suggested that theoptical transitions due toZeeman splitting could provide a way to study ferromagnetic structure.FMR is very similar tonuclear magnetic resonance except FMR probes themagnetic moment ofelectron s and NMR probes the magnetic moment of atomic nuclei.FMR arises from the precessional motion of a ferromagnetic material in an external magnetic field. The magnetic field puts a
torque on the magnetization which causes the magnetic moment toprecess . The precession frequency depends on the orientation of the material and the strength of the magnetic field.The basic setup for an FMR experiment is a microwave
resonant cavity with anelectromagnet . The resonant cavity is fixed at a frequency in thesuper high frequency band. A detector is placed at the end of the cavity to detect the microwaves. The magnetic sample is placed between the poles of the electromagnet and themagnetic field is swept while the intensity of the microwaves are detected. When the precession frequency and the resonant cavity frequency are the same, absorption increases indicated by a decrease in intensity in the detector.References
* S. V. Vonsovskii, "Ferromagnetic Resonance" (Pergamon: Oxford, 1966).
* S. Chikazumi, "Physics of Ferromagnetism" (Oxford: New York, 1996).See also
*
Electron paramagnetic resonance
Wikimedia Foundation. 2010.
