Commensurate magnetic structure of CeRhIn_4.85Hg_0.15

We show using neutron diffraction that the magnetic structure of CeRhIn_4.85Hg_0.15 is characterized by a commensurate propagation vector (1/2,1/2,1/2). This is different from the magnetic structure in the parent compound CeRhIn₅, which orders with an incommensurate propagation vector (1/2,1/2,0.297). The special relation between the commensurate magnetic mode and unconventional superconductivity has been shown previously for this class of heavy fermion superconductors. This work provides further evidence for the ubiquity of this antiferromagnetic mode.