Huge influence of hydrogenation on the magnetic properties and structures of the ternary silicide NdMnSi

The hydride NdMnSiH obtained by exposure of the ternary silicide NdMnSi under a pressure of 4 MPa of hydrogen at 523 K crystallizes in the tetragonal ZrCuSiAs-type structure where H atom occupies the tetrahedral $[Nd4]$ sites. The hydrogenation of NdMnSi induces an increase in the unit cell volume close to 3.3%. The investigation of NdMnSiH by magnetization and specific heat measurements reveals the existence of two antiferromagnetic ordering, respectively, at $TN1=565(5)K$ and $TN2=103(4)K$⁠. Neutron powder diffraction shows that these Néel temperatures are associated with an antiferromagnetic arrangement of the (i) Mn substructure $(TN1)$ and (ii) Nd substructure linked to a reorientation of the Mn one $(TN2)$⁠. Comparison of the $TN1$ and $TN2$ temperatures of NdMnSiH to those reported for the initial compound NdMnSi indicates a strong increase in $TN1$ $(280K→565K)$ and a significant decrease in $TN2$ $(185K→103K)$⁠. The magnetic properties, magnetic structures, and values of Nd and Mn ordered magnetic moments are discussed using both band structure calculations and comparison with the behaviors of other ternary silicides and germanides based on manganese and rare earth elements.