Crystal distortions in geometrically frustrated ACr2O4 (A = Zn,Cd)

In this paper, we discuss neutron and synchrotron x-ray diffraction data obtained from single crystals of ACr2O4 (A = Zn, Cd). The Cr spinels undergo three-dimensional spin-Peierls transitions at low temperatures that involve cubic-to-tetragonal lattice distortions and magnetic long-range ordering. Our results show that the magnetic structures selected by these systems are closely related to the lattice distortions that are undertaken.