Determination of the orbital moment in the Jeff=1/2 3d-metal pyrochlore antiferromagnet NaCdCo2F7 & possible Jeff=1/2 ground-state in the 3d-metal pyrochlore antiferromagnet NaCdCu2F7

The proposal is targeted at the measurement of the X-ray Magnetic Circular Dichroism (XMCD) of cobalt (Co) and copper (Cu) at the L2,3-edge to probe the origin of the large effective magnetic moment seen in the Jeff = ½ pyrochlore spin-glass NaCdCo2F7; and to determine the true ground-state (S = ½ or Jeff = ½) of the pyrochlore quantum spin liquid candidate NaCdCu2F7. Both of these compounds hint at a non-zero orbital contribution to the magnetic moment, thus understanding the origin of this effect and its implications on the anisotropy of magnetic interactions will be essential. It could help explain the XY-type anisotropy seen in the previously-studied isostructural Co2+-based Jeff = ½ compounds NaA’Co2F7 (A’ = Ca, Sr), which lead to a spin-glass ground-state with distinctive relaxation dynamics, composed of short-range-ordered XY clusters below Tf ~ 2.4 K. The slightly larger magnetic moment of Cu2+ than the expected S = ½ value with orbital quenching could suggest that the trigonal distortion of the octahedral crystal field along the local [111] direction, confirmed by our single-crystal XRD measurements, and combined with the spin-orbit coupling effects, could instead lead to a Jeff = ½ ground-state with a non-zero orbital contribution.