MN-55 NMR-STUDY OF THE GDMN2 HYDRIDES

The Mn-55 NMR spin-echo spectra for the cubic GdMn2Hx compounds with x =0, 0.5, 1, 2, 2.5, 3, 3.4, 3.5 and for the rhombohedral GdMn2H4.3 are reported. For thr samples with x=0, 0.5, and 1 spectra with a single broad line at 129, 132, and 135 MHz, respectively are observed. Satell ite patterns with up to three lines are observed for 2<x<3.5. The effe ct is attributed to a diversification of manganese moments caused by h ydrogen neighbors leading lu up to three values of the Mn moment in th e cubic hydrides with x>2.5. For GdMn2H3.5 the directions of Mn magnet ic moments with respect io the magnetization are derived from the Line shifts in an applied magnetic field. The two narrow lines observed fo r the rhombohedral compound GdMn2H4.3 at 186 and 423 MHz an attributed to the two Mn sites in the structure. The observed effects are explai ned by the presence of four different magnetic structures and four man ganese spin states in the series.