Frustrated magnetism in octahedra-based Ce6Ni6P17

Magnetic frustration allows to access novel and intriguing properties of magnetic systems and has been explored mainly in planar triangular-like arrays of magnetic ions. In this work, we describe the phosphide ${\mathrm{Ce}}_{6}{\mathrm{Ni}}_{6}{\mathrm{P}}_{17}$, where the ${\mathrm{Ce}}^{+3}$ ions accommodate in a body-centered cubic lattice of ${\mathrm{Ce}}_{6}$ regular octahedra. From measurements of magnetization, specific heat, and resistivity, we determine a rich phase diagram as a function of temperature and magnetic field in which different magnetic phases are found. Besides clear evidence of magnetic frustration is obtained from entropy analysis. At zero field, a second-order antiferromagnetic transition occurs at ${T}_{{N}_{1}}\ensuremath{\approx}1$ K followed by a first-order transition at ${T}_{{N}_{2}}\ensuremath{\approx}0.45$ K. With magnetic field new magnetic phases appear, including a weakly first-order transition which ends in a classical critical point and a third magnetic phase. We also study the exact solution of the spin-1/2 Heisenberg model in an octahedron which allows us a qualitative understanding of the phase diagram and compare with the experimental results.