Magnetic relaxation of hydrogen in La(Ni0.7Fe0.3)5

The short-range hydrogen diffusion in the α-phase of the intermetallic compound La(Ni0.7Fe0.3)5 has been studied by means of magnetic after-effect (MAE) measurements below the Curie temperature Tc=250 K. At a hydrogen concentration of cH=4.7 at.% the MAE spectrum shows one broad relaxation maximum at 125 K, with an activation enthalpy of Q=(0.32±0.02) eV and a pre-exponential factor of τ0=2 x 10-12±0.5 s. With lower hydrogen content this maximum shifts to higher temperatures corresponding to an increase of the activating enthalpy. At a concentration of cH=0.4 at.% it splits up into a double maximum at 140 and 160 K. The corresponding enthalpy spectrum shows two peaks with activation enthalpies of (0.36±0.03) and (0.43±0.03) eV. The results are discussed taking into account the crystal structure of the AB5 compound and hydrogen-induced internal stresses. (orig.)