Magnetic properties and microstructure of sputtered CoSm/X (X=Ti, V, Cu and Cr) thin films

The effects of underlayer materials Cr, Ti, V and Cu on the magnetic properties such as coercivity and the microstructure of Co/sub 85/Sm/sub 15/ films deposited onto these underlayers were investigated. A coercivity as high as 3600 Oe was obtained in the Co/sub 85/Sm/sub 15/ film with a 100 nm thick Cr underlayer, but it was about 1800-2600 Oe in the cases of Ti, V and Cu underlayers with the same thicknesses. Cross-section TEM observation revealed that a clear columnar structure is formed for the Cr underlayer but not clearly for the other underlayers. High resolution TEM observation indicated that the CoSm film with Cr underlayer consists of amorphous columns and crystalline boundaries surrounding those columns. It was considered that this heterogeneous structure gives rise to the large coercivity in the case of the Cr underlayer.>