Mössbauer effect investigations of the electronic and magnetic properties of rare earth metal and intermetallic hydrides

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Abstract
Mössbauer spectroscopy has been used in a number of investigations of elemental rare earth (RE) metal and RE–transition metal intermetallic hydrides. Analysis of hyperfine parameters has established the crystalline electric field (CEF) ground state for Dy3+ in DyH2 and for Er3+ in ErH2 and YH2. In all cases the results are compatible with the presence of negatively charged hydrogen atoms. Long range magnetic ordering is observed in the RE‐H2 compounds. In DyH2, short‐range magnetic ordering is seen at temperatures up to twice the long‐range transition temperature. This arises from the changes in CEF symmetry due to the presence of a few H atoms which are not in regular tetrahedral sites. These effects are much more pronounced in slightly non‐stoichiometric compounds and can result in dramatic changes in the magnetic ordering temperature. As an example of an intermetallic hydride, we have studied the cubic Laves phase RE‐iron compounds. These form several stable hydride phases RE‐Fe2Hx, with the maximum x being in excess of 4. The magnetic transition temperatures decrease to roughly half their original values for x=3.5, and the RE‐Fe exchange interaction is weakened. For x=4, a sharp reduction in both the Fe magnetic moment and the magnetic ordering temperature occurs.