Valence and magnetic degrees of freedom in low-T instabilities of CuCr2(S/Se)4

We are investigating ferromagnetic spinel materials in which the distribution of valences across interpenetrating 3d-transition-metal lattices has long been subject to debate. Having observed unusual low-temperature transitions by other methods, the key question is whether these involve changes of the valence distribution, or changes of the distribution of the ordered magnetic moments over the 3d ions (Cu and Cr). The HECTOR XAS/XMCD spectrometer is ideally suited to answer these questions.