Perspective on synthesis, structure, and magnetic properties of R–Fe–H hydrides

The structural and magnetic properties of the multicomponent R–Fe–H compounds with a high content of Fe and H are reported. The process of synthesis of the hydrides (R,R`)<sub>2</sub>Fe<sub>14</sub>BH<sub>5.5</sub> [where R and R` are light (Nd) and heavy (Dy, Ho, Er, Tm) rare earth metals, respectively] with a maximum hydrogen content is described in detail. The paper also provides insights into the synthesis of single-crystalline hydrides using the example of the R₂(Fe,Co)₁₄BH₃ series. The hydrides (R,Nd)₂Fe₁₄BH_5.5, R₂(Fe,Co)₁₄BH₃, R₂(Fe,Al)₁₇H₃ have a significantly increased volume as compared to the parent materials. High-field magnetization results of both parent and hydrogenated compounds at low temperatures are presented. Spin–reorientation phase transitions induced by an external magnetic field are observed. The parameter of the intersublattice exchange interaction and the influence of hydrogen on it are estimated within the framework of the mean field theory. The magnetocaloric effect of the compounds with a magnetic compensation point is studied with a special emphasis placed on the change of the sign of the effect.