Magnetic properties of the beta- and beta '-ytterbium hydride phases

Samples of the beta -ytterbium hydride phase with compositions 2.2 <H/Yb le ss than or equal to2.71 were prepared and their magnetic properties studied . Measurements of the magnetization vs. temperature were carried out in the range 1.75-300 K. The magnetization plots proved the presence of the maxim um at around 4 K and the Curie-Weiss like behaviour at high temperatures. T he magnetic moment per Yb atom exhibits an almost constant value of 3.85 +/ - 0.05 mu (H) for various compositions across the beta -ytterbium hydride p hase. This effective moment is smaller than the ionic Hund's rule moment of 4.54 mu (H) expected. for trivalent Yb3+ ions and clearly indicates that t he Yb atoms stay in an intermediate valence state. The average valence of Y b ions v(Yb)=2.72 +/-0.02 calculated from magnetic data is independent on t he hydrogen concentration and lie between the expected values for the corre sponding pure valent Yb2+ and Yb3+ ions. For the first time, the magnetic p roperties of the beta'-ytterbium hydride phase are also measured and discus sed as well. The obtained results indicate that the ytterbium atoms in the cubic beta'-hydride phase are trivalent like the light lanthanide elements in their hydride phases. (C) 2001 Elsevier Science B.V. All rights reserved .