I am working on FeNi alloys and would like to measure the exchange constant. My samples are powdered.
What methods are there to measure it and what are the advantages or disadvantages of the methods?
There is no direct measurement of the exchange coupling. In your case I would compare the paramagnetic susceptibilities - the exchange constant at Q=0 is proportional to the asymptotic paramagnetic Curie temperature you'll get from a Curie-Weiss fit.
The best way to determine the exchange coupling is to measure the magnon dispersion with neutron spectroscopy and model it. This normally requires single crystals.
May be the attached article can help you.
With my best regards,
Pedro
You need to do a neutron scattering measurement of spin wave propagation, then you can deduce the exchange parameters using Holstein-Primakoff transformation (see the link below)
http://journals.aps.org/pr/abstract/10.1103/PhysRev.58.1098
This paper also may help you (F. Moussa, M. Hennion, J. Rodriguez-Carvajal, and H. Moudden "Spin waves in the antiferromagnet perovskite LaMnO 3 : A neutron-scattering study", Phys. Rev B 54 no 21 (1996))
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