Magnetic phase diagram of the stage-1 ${\mathrm{CoCl}}_2$ graphite intercalation compound: Existence of metamagnetic transition and spin-flop transitions

The $H-T$ phase diagram of a stage-1 ${\mathrm{CoCl}}_2$ graphite intercalation compound has been determined from measurements of the ac magnetic susceptibility, dc magnetization, and in-plane resistivity in the presence of an external magnetic field along the c plane perpendicular to the c axis. This compound undergoes two magnetic phase transitions at $T_{\mathrm{cu}}$ ${(=T}_N=9.9\mathrm{}\mathrm{K})$ and $T_{\mathrm{cl}}$ $(=7.7\mathrm{}\mathrm{K})$ at $H=0.\mathrm{}$ A metamagnetic transition occurs at a critical point ${(T}_3\approx 8.77\mathrm{K},$ $H_3\approx 270\mathrm{Oe}).\mathrm{}$ A spin-flop transition occurs at the critical point ${(T}_2\approx 6.8\mathrm{}\mathrm{K},$ $H_2\approx 80\mathrm{Oe})$ due to a competition between weak antiferromagnetic interplanar interactions and in-plane anisotropic interactions. Two lines $H_{+}$ and $H_{-}$ above $T_N$ are due to ferromagnetic short-range fluctuations.