Temperature-Dependent Sinusoidal Magnetic Order in the Superconductor HoMo6Se8

A magnetic phase transition ($T_M=0.53\mathrm{}$ K) to a long-period (∼${10}^2$-Å) magnetic state has been observed via neutron scattering in the superconductor ($T_c=5.6\mathrm{}$ K) Ho${\mathrm{Mo}}_6$ ${\mathrm{Se}}_8$. The characteristic wave vector $q_c$ is strongly temperature dependent even though no higher-order satellites are observed. With use of a Ginzburg-Landau model it is found that the temperature dependence of $q_c$ can be explained as due to a renormalization of the superconducting order parameter caused by the coupling to the local magnetization density.