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The influence of hydrogen absorption on the electronic and magnetic states of nickel was investigated by using the magnetic Compton scattering method, associated with band structure calculation. Hydrogen-free, hydrogen-charged and hydrogen-discharging nickel foils were prepared in an electrochemical cell, then their magnetic Compton profiles (MCPs) were measured with circularly polarized 173 keV X-rays in magnetic fields of ±2.5 T at room temperature in situ. The MCP of the hydrogen-charged nickel was separated into the respective profiles of α-phase NiH0.03 and β-phase NiH0.7. The MCP of the β-phase NiH0.7 indicates that this hydride is weakly ferromagnetic with a small spin moment µ<0.1 µB/Ni where the positive d-like component is nearly cancelled out by the negative s,p-like component. The band structure calculation yields such a small moment in the hydrogen-ordered NiH0.75, but smaller absolute values of the d-like and the sp-like components than the observed ones.

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