Magnetic systems are fertile ground for the emergence of exotic states when the magnetic interactions cannot be satisfied simultaneously due to the topology of the lattice - a situation known as geometrical frustration. Spinels, AB2O4, can realize the most highly frustrated network of corner-sharing tetrahedra. Several novel states have been discovered in spinels, such as composite spin clusters and novel charge-ordered states. Here we use neutron and synchrotron X-ray scattering to characterize the fractional magnetization state of HgCr2O4 under an external magnetic field, H. When the field is applied in its Neel ground state, a phase transition occurs at H ~ 10 Tesla at which each tetrahedron changes from a canted Neel state to a fractional spin state with the total spin, Stet, of S/2 and the lattice undergoes orthorhombic to cubic symmetry change. Our results provide the microscopic one-to-one correspondence between the spin state and the lattice distortion.
@article{arxiv.0707.0280,
title = {Spin-lattice instability to a fractional magnetization state in the spinel HgCr2O4},
author = {M. Matsuda and H. Ueda and A. Kikkawa and Y. Tanaka and K. Katsumata and Y. Narumi and T. Inami and Y. Ueda and S. -H. Lee},
journal= {arXiv preprint arXiv:0707.0280},
year = {2015}
}