Structure and Magnetic Properties of RF Sputtered Fe_1-xNi_x/Cu Superlattices

Applying ny sputtering techniques, a series of fcc (Fe_1-xNi_x/Cu)₁₀ superlattices are prepared with Ni concentrations x ranging from 0.26 to 0.54. The use of MgO single crystal substrates and Cu sublayers in the superlattice growth ensure well defined fcc crystal structures in the Fe-Ni sublayers with a Ni concentration as low as 26% and down to liquid helium temperatures.The magnetization of the Fe-Ni sublayers in the super-lattices is reduced when the composition of the Fe-Ni layers approaches the Invar composition, i.e., it shows a deviation from the well-known Slater-Pauling curve. Strong dependence of magnetization on temperature is also observed for the Fe-Ni sublayers with Invar compositions, consistent with the behavior of the bulk Fe-Ni Invar alloys. It is concluded that the deviation of magnetic moment of FeNi alloys near the Invar composition may not be attributed to the so-called premartensitic transformation, but to the Fe-Fe antiferromagnetic interactions in the alloys.