A study on the effect of hydrogen in the compounds with BaCd11-type structure

A study on the crystallographic and magnetic properties of the BaCd11-type RFe9Si2CxHf (R=Ce, Nd, Sm; x=0.5, 1.0, 1.5; f denotes full occupation) have been carried out. The hydrogen insertion dilates the volume, and the expansion in the basal plane is larger than that along the c-axis: (Δa)/a≈0.3%, (Δc)/c≈0.1%. Both the Curie temperature and the saturation magnetization increase with the hydrogen insertion. For the Ce and the Nd compounds, the easy magnetization direction (EMD) lies in the basal plane, and for the Sm compounds, the EMD is along the c-axis. The anisotropy field of the Sm compounds decreases with the hydrogen insertion. The exchange interaction coefficients are also calculated with the molecular field model. Both the rare-earth–iron exchange interaction nRFe and the iron–iron exchange interaction nFeFe increases with the increasing carbon content and the hydrogen insertion. Furthermore, the first order magnetization process (FOMP) is observed in NdFe9Si2Cx and their corresponding hydrides.