Diffuse Scattering Spectrometer

 D7 has been dismantled.  The new permanently-polarized diffuse scattering spectrometer D007 will deliver its first neutrons in 2024.

Magnetism in Molybdate Pyrochlores

Pyrochlores are compounds with the generic stoichiometry A2B2O7 and the crystal space group Fm-3m.  Magnetic pyrochlores are currently heavily researched as the forces between the magnetic ions they contain compete with one another, leading to magnetic 'frustration' and a large variety of exotic magnetic behaviour.  The magnetism can be better described by mean-field or 'classical' theories if the moments are larger, but quantum physics - a subject of great current interest - is necessary of the moments become very small.  
Experiments on samples with small moments is very difficult because the magnetic signal is small and can be easily lost in scattering from other contributions.  By using polarization analysis, D7 is able to separate small magnetic signals, making it remarkably sensitive.  In the example here, the authors wished to observe the magnetic scattering from powdered samples of the small-moment pyrochlores Lu2Mo2O7 and Lu2Mo2O5N2.  The data show that D7 can observe scattering from 0.11 μB per formula unit, or 0.055 μB per Mo ion.

Ref: L. Clark, G. J. Nilsen, E. Kermarrec, G. Ehlers, K. S. Knight, A. Harrison, J. P. Attfield, and B. D. Gaulin, Phys. Rev. Lett. 113 117201, (2014)