Recently synthesized metastable tetragonal CoSe, isostructural to the FeSe superconductor, offers a new avenue for investigating systems in close proximity to the iron-based superconductors. We present magnetic and transport property measurements on powders and single crystals of CoSe. High field magnetic susceptibility measurements indicate a suppression of the previously reported 10 K ferromagnetic transition with the magnetic susceptibility, exhibiting time dependence below the proposed transition. Dynamic scaling analysis of the time dependence yields a critical relaxation time of ${\tau }^{*}=0.064\pm 0.008$ s which in turn yields activation energy $E_a^{*}=14.84\pm 0.59$ K and an ideal glass temperature $T_0^{*}=8.91\pm 0.09$ K from Vogel-Fulcher analysis. No transition is observed in resistivity and specific heat measurements, but both measurements indicate that CoSe is metallic. These results are interpreted on the basis of CoSe exhibiting frustrated magnetic ordering arising from competing magnetic interactions. Arrott analysis of single crystal magnetic susceptibility has indicated the transition temperature occurs in close proximity to previous reports and that the magnetic moment lies solely in the $ab$ plane. The results have implications for understanding the relationship between magnetism and transport properties in the iron chalcogenide superconductors.

• Received 15 November 2017

DOI:https://doi.org/10.1103/PhysRevB.97.104408