Exchange Enhancement of Pd Coating on Ni Fine Particles

Magnetic and structural properties of Ni fine particles (0.7±0.2 μm in diameter) coated with Pd (5 nm∼37 nm in thickness) were investigated in a hydrogen atmosphere by means of magnetometry and X-ray diffractometry. The spontaneous magnetic moment is newly induced on the Pd atoms even at room temperature by the magnetic proximity effect between Ni core and Pd layer. Relatively large coercive force indicates the presence of the interface anisotropy. The magnetic polarization and the coercive force are suppressed by the hydrogenation. The temperature dependence of the magnetization shows a broad maximum around 80 K and an increase below 50 K. The maximum in magnetization is due to the enhanced paramagnetic contribution of Pd, and the gradual increase below 50 K is due to the Ni moment in contact with ferromagnetic Pd. A model for layered magnetic structure of the Ni particles coated with Pd is proposed.