We have prepared amorphous Tb20Fe80/Al2O3 multilayer films by rf sputtering onto water‐cooled glass substrates using 100‐W rf power and argon pressure of 6 mT. The thickness of the Al2O3 layer was kept constant at 4 nm and that of Tb‐Fe (denoted as d) was varied from 4 to 10 nm. The total number of bilayers was in the range 10–15. A single layer of Tb‐Fe of 200 nm was also prepared to serve as a reference. All the films were given a protective Al2O3 layer of about 15 nm thick. Magnetization (M) and a hysteresis loop were obtained using a VSM. Uniaxial anisotropy (Ku) and M were measured with a torque meter. Polar Kerr loops were taken with a HeNe laser. For d>6 nm M remains the same but increases sharply for d<6 nm. This is attributed to preferential oxidation of Tb in very thin layers. Ku increases from 0.6 to 1.2×106 ergs cm3 when d increases from 4 to 7 nm and remains so for thicker films. Though Ku appears even for thinner layers, the coercivity remains low (0.2–0.6 kOe) but attains a value of 2 kOe only for d>8 nm. This would indicate that the microscopic mechanisms for these two properties are not the same. Finally, only samples with d>8 nm show all the characteristics of the thick single layer. Detailed analysis of the torque curves will be presented.

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