MOSSBAUER-EFFECT STUDY OF THE MAGNETIC-ORDERING IN GDMN2HX

By means of Fe-57 Mossbauer spectroscopy, values of the average isomer shifts at 4.2 and 300 K, the average hyperfine field at 4.2 K and the magnetic ordering temperatures were measured for Gd((Fe0.01Mn0.99)-Fe -57)(2)H-x (0 less than or equal to x less than or equal to 4.2). The relative importance of the volume expansion and band effects due to hy drogen absorption were deduced from isomer shift changes. The nonlinea r increase of the magnetic ordering temperature values versus x and ab rupt increase of the average hyperfine field for x greater than or equ al to 2.5 were revealed. Using YMn2Hx, results as reference, the magni tude of the 4f-3d interaction versus Mn-Mn distance for GdMn2Hx was in ferred. (C) 1998 Elsevier Science B.V. All rights reserved.