In this work, we perform a comparative study of the magnetization behavior of four series of compounds R2Fe14B and their hydrides R2Fe14BH5.5, and the compositions (Nd0.5R0.5)(2)Fe14B and their hydrides (Nd0.5R0.5')(2)Fe14BH5.(5) with R and R' = Ho, Er, and Tm. The magnetization is measured in pulsed magnetic fields up to 58 T and in megagauss fields up to 135 T at 5 K.
The first and second critical fields of the field-induced transitions, H-c1 and H-c2 were estimated analytically and the results were verified against experimental data. We find that hydrogenation of R2Fe14B and (Nd0.5R0.5')(2)Fe14B reduces drastically the H-c1 and H(c2 )values and, as a consequence, the intersublattice R-Fe exchange interaction parameter lambda.