Single crystal study of the one dimensional Ca_3Co_2O_6 compound: five stable configurations for the Ising triangular lattice

摘要

Single crystals of the one-dimensional phase Ca_3Co_2O_6 of several mm length have been grown. The magnetic study of such a crystal confirms the previous observations on polycrystalline samples: it consists of a triangular lattice of ferromagnetic [Co_2O_6] chains (T(C1) = 24 K) antiferromagnetically coupled (T_(C2) = 12 K). The dynamic of these chains array, probed by AC susceptibility, is very slow as shown from the large shift of the freezing temperature from 12 K to 16.5 K as the excitation frequency increases by three orders of magnitude (10~0 to 10~3 Hz). The origin of this effect is believed to be the result of different arrangements with close energies for the chain ferromagnetic moments on the triangular lattice. Five stable magnetic configurations have been evidenced by the magnetization as a function of applied field curves registered at 2 K. Their relative magnetizations correspond to m = 1/4, 1/2, 1, 2, 3 where m = 3 represents the ferromagnetic ordering of three chains of on the same triangle, each chain having a m = 1 magnetization. A magnetic phase diagram is finally proposed.