Structural and magneto-optical properties of Tb/Fe and (Tb/Fe)/Si3N4 multilayers

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Abstract
Tb/Fe and (Tb/Fe)/Si3N4 multilayer films with layers in the nanometric range have been prepared using a reactive diode rf sputtering system. Their structural and magneto-optical properties have been investigated to determine the stack parameters, the crystallization states, the direction of easy magnetization, and the Kerr angle values. The multilayer structure can be observed even when terbium layers are about 0.2 nm thick. Iron crystallization appears to depend on the terbium layer thickness. For Tb layer thicknesses greater than 0.37 nm, iron is amorphous when thinner than 3 nm. It spontaneously crystallizes when the layer becomes thicker. When Tb layer thickness is smaller than 0.37 nm, Fe crystallization is always detected: It occurs in the whole stack through the incomplete Tb layers. Kerr rotation measurements show a magnetic anisotropy depending on the Tb/Fe thickness ratio. Indeed, the direction of easy magnetization was found to be in the plane of the samples for ratio values of about 0.23 and 1.5, and rather perpendicular for ratio values of about 1. A Kerr angle of 1.2° has been obtained on a (Tb/Fe)/Si3N4 multilayer film in a nonsaturated magnetic state (λ=632.8 nm).