Magnetization and its temperature dependence in compositionally modulated amorphous Fe70B30-Ag films

Compositionally modulated amorphous Fe70B30-Ag films have been prepared by dc magnetron sputtering. The thickness of the magnetic layer (d) ranged from 3 to 90 Å, while the Ag layer thickness was always kept at four times as large. The multilayer structure is well established by the cross-sectional transmission electron micrograph. The magnetic properties of the system were investigated with a SQUID magnetometer. The spontaneous magnetization (Ms) at T=8 K remains constant over the thickness range studied, indicating the absence of magnetically dead layers at the interfaces. The temperature dependence of Ms follows Bloch’s law for d≥6 Å, with the spin-wave constant inversely proportional to d. This is explained by an interface effect on spin-wave excitation. As the thickness is reduced to 4 Å, a linear temperature dependence of Ms is observed, indicating a magnetic 3D-to-2D transition.