Hydrogen absorption and field-dependent diamagnetism of SmNiAl

Hydrogen absorption properties of SmNiAl were systematically investigated between room temperature and 673 K over the pressure range from 0 to 10 MPa. It absorbs hydrogen without clear plateaus, forms hydride SmNiAlHx (x=0.75–2.04) without structural change below 623 K and decomposes into SmH2 and NiAl at higher temperatures. Then, the magnetic curves, the field-cooled (FC) and the zero-field-cooled (ZFC) susceptibilities of SmNiAl and its hydride were investigated. SmNiAl behaves as paramagnetic above 65 K, but has three antiferromagnetic transitions at lower temperatures. Hydrogenation enhances its magnetism, but weakens the interaction between magnetic moments. In the FC process, hydrogenation especially induces an anomalous diamagnetism. Mechanisms for the hydrogen absorption, structural change and magnetism were discussed.