Effects of Separation and Cap Layers on the Magnetic Properties of Arrays of Square Nd-Fe-B Thin Films

Patterns of Nd-Fe-B thin-film squares were prepared by electron-beam lithography and Ar-ion etching, after which cap layers of MgO, Al/MgO, or FeGa/MgO were deposited. The separation of the squares was varied from 20 to 80 nm. The relationship among separation distance, cap-layer material, and magnetic properties was investigated. The coercivity increased from 9.8 kOe for a continuous Nd-Fe-B film to 12.8 kOe for a microfabricated square pattern with separation distance of 40 nm and Al (10 nm) or MgO (10 nm) cap layers. However, the coercivity dramatically decreased for patterns with FeGa (10 nm) and MgO (10 nm) cap layers.