Variation of the intersublattice exchange coupling due to hydrogen absorption in Er₂Fe₁₄B: A high-field magnetization study

Single crystals of a series of hydrides Er₂Fe₁₄BH_x (x ≤ 2.5) have been produced and studied in pulsed magnetic fields up to 60 T. The magnetization curve of Er₂Fe₁₄B in the easy direction [100] features a stepwise anomaly at about 45 T, corresponding to the first-order phase transition. A similar magnetization jump is also present in the curve along [110], but at a higher field, ∼52 T. The [100] data of the parent and hydrogen-charged Er₂Fe₁₄BH_x with x = 0.25, 1.5, 2.5 were used to deduce the Er-Fe molecular field H_mol as a function of hydrogen content x. After moderate initial decrease, H_mol(x) drops abruptly above x = 1.5. Hydrogenation results in a 12% reduction of the Er-Fe molecular field in Er₂Fe₁₄BH_2.5 as compared to Er₂Fe₁₄B. For reference, influence of hydrogen on Hmol in an Er₂Fe₁₇-H system is also presented