Magnetic phase diagram of Ca_1-xMn_xO

Alternating current susceptibility and direct current magnetization have been studied for polycrystalline Ca$_{1-x}$Mn$_x$O. On increasing the Mn content, magnetic ordering changes from spin-glass behavior for $0.25 \leqslant x \leqslant 0.4$ to antiferromagnetic order. The paramagnetic/antiferromagnetic transition is of second order for $0.5 \leqslant x \leqslant 0.65$ and of first order for $x \geqslant 0.7$. For low Mn concentrations, the high-temperature alternating current susceptibility can be described by a diluted Heisenberg magnet model developed for diluted magnetic semiconductors.