Magnetic, magneto-optical and dynamic characteristics of exchanged-coupled NdTbFeCo/TbFeCo films for 532 nm recording media

A magnetic, magneto-optical and structural study was performed on exchanged-coupled (EC) layers between NdTbFeCo and TbFeCo films for 532 nm recording media. The saturation magnetization (Ms) of separate read-out (RO) and storage (ST) films varied from 177 to 269 emu/cm² and from 73 to 87 emu/cm², respectively, in the sputtering power range 0.4 to 0.73 kW, at a fixed Ar gas flow rate. Coercivity (Hc) and Kerr angle (θ_k) of RO were in the range 0.46 kOe to 0.65 kOe and 0.34° to 0.38°, respectively, for Ar gas flow rate between 15 to 40 sccm, and no great changes were found in the surface morphologies, as observed with atomic force microscopy (AFM). Hc and squareness rose from 2 kOe to 6 kOe and 0.6 to 0.98 with increasing R from 1.5 to 8, where R is the thickness ratio of NdTbFeCo to TbFeCo (total thickness 200 Å, 250 Å) in the five layered system SiN_x/NdTbFeCo/TbFeCo/SiN_x/Al-Ti. The carrier-to-noise ratio (CNR) increased by about 8 dB, as R was raised from 1.5 to 3. The films were prepared by magnetron rf-dc continuous sputtering. No atomic mixing between NdTbFeCo and TbFeCo layer occurred, as confirmed by TEM cross sectional observations