Modulated magnetic structures of the antiferromagnetic hydride CeRuSiH

The hydride CeRuSiH is derived from the non-magnetic heavy-fermion ternary silicide CeRuSi that crystallizes in the tetragonal CeFeSi-type structure (P4/nmm space group). This hydride exhibits two antiferromagnetic transitions at TN1 = 7.5(2) K and TN2 = 3.1(2) K, evidenced by magnetization and specific heat measurements. Crystal and magnetic structures of CeRuSiH have thus been investigated by means of neutron powder diffraction, which has shown firstly that H-atoms are fully inserted in the [Ce4]-tetrahedra. Moreover, between TN1 and TN2, the Ce magnetic moments are ordered in a collinear antiferromagnetic sinusoidal structure associated with the propagation vector k = (kx, kx,1/2) (kx<1/3 and tends to 1/3 with decreasing temperature). At TN2, the magnetic structure becomes square wave modulated and commensurate with k = (1/3,1/3,1/2) as propagation vector. At 1.5 K, the structure is antiphase with a Ce magnetic moment of 1.68(2) μB. These magnetic structures are compared with those previously reported on the substituted ternary silicides (Ce1-xLax)Ru2Si2 and CeRu2(Si1-xGex)2, which also present an antiferromagnetic behaviour