Mechanical alloying, nitrogen storage and magnetization of Ca–Co powder

Mechanical alloying was performed on the Ca–Co system and the nitrogen storage property and magnetization were investigated. The solid solution of Co dissolving Ca is formed during MA process that has limited storage ability, while longer milling produces amorphous/nanocrystalline phase with the ability. The milled Ca–Co powder absorbed and desorbed more nitrogen than pure Ca and Co powder each separately milled and processed. The increase of Ca surface area mainly controls the storage property for short MA, while that for longer MA is ascribed to the non-equilibrium phase. The stored amount for Ca–Co powder increases with milling time, and its magnetization significantly decreased. The large reduction is explained by linear dilution of atomic moment based on the rigid band model, while the deviation from the model for longer MA is explained by formation of the non-equilibrium phase with limited magnetization but with nitrogen storage ability.