Physical properties including magnetic susceptibility, room-temperature electrical resistivity, thermal conductivity, heat capacity, and thermal expansion are reported for high quality single-crystal samples of marokite ${\text{CaMn}}_2{\text{O}}_4$. We determined that ${\text{CaMn}}_2{\text{O}}_4$ is highly electrically insulating and exhibits long-range antiferromagnetic order below $T_N=217.5\pm 0.6\text{K}$ with easy axis along $a$. Anisotropic thermal expansion, similar to that of crystallographically layered materials, is observed, suggesting that the crystal structure of ${\text{CaMn}}_2{\text{O}}_4$ is also assembled from previously undescribed layers. An extensive thermodynamic study of the antiferromagnetic transition was undertaken resulting in a heat-capacity critical exponent $\alpha =0.082\pm 0.007$ and calculated pressure derivative $d{T}_N/dP=5.154\pm 0.174\text{K}/\text{GPa}$.

• Received 9 December 2008

DOI:https://doi.org/10.1103/PhysRevB.79.104427