Magnetic order in superconducting TbMo6S8, DyMo6S8, and ErMo6S8

Abstract

Dy${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ and Tb${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ are superconducting below $T_c=2.05\mathrm{}$ K, and Er${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ below $T_c=2.2\mathrm{}$ K. Neutron diffraction has been used to study the development of magnetic order in these materials at temperatures $T_M$ less than $T_c$. In zero applied magnetic field, the Dy${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ and Tb${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ order antiferromagnetically, the magnetic order coexisting with the superconductivity. The Er${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ sample showed no long-range magnetic order when initially cooled down in zero applied magnetic field. After a magnetic field was applied and reduced to near zero, the sample showed coexistent antiferromagnetic order below $T_M=0.2\mathrm{}$ K. Magnetization measurements on Dy${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ and Tb${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ at temperatures below $T_M$ suggest the development of ferromagnetic order as the applied field increases. In the case of Tb${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$, the neutron data show ferromagnetic order developing for $H>~H_{c2\mathrm{}}$ where $H_{c2\mathrm{}}$ is the upper critical field for superconductivity. For Dy${\mathrm{Mo}}_6$ ${\mathrm{S}}_8$ ferromagnetic order develops for $H$ much less than $H_{c2\mathrm{}}$. Both ferromagnetic and antiferromagnetic order occur with the sample in the superconducting state.