Effect of Chemisorbed Hydrogen on the Magnetization of Nickel at Low Temperatures

Abstract

The saturation magnetization of nickel particles in the range 10–100 A has been determined by extrapolating from magnetizations measured at 4.2°K in fields up to 104 oersteds. Measurements have been made prior to, and after, the admission of hydrogen to the nickel at room temperature. The nickel is supported on silica in the manner familiar in heterogeneous catalysis. The number of d electrons paired per hydrogen atom adsorbed has been calculated from the fractional change in saturation magnetization assuming the magnetic moment per atom of nickel to be 0.606 Bohr magneton. The ratio of d electrons paired to hydrogen atoms adsorbed has been shown to be less than one. On sintered samples in which the average nickel particle diameter is 40–80 A the ratio is about 0.7. On smaller nickel particles the ratio may be less. This ratio does not appear to be sensitive to surface coverage. The fact that the ratio of d electrons paired to hydrogen atoms adsorbed is less than one is considered evidence for a localization of the electronic interaction between adsorbent and adsorbate.