Optimization of Ultra-Thin Pulsed-DC Magnetron Sputtered Aluminum Films for the Technology of Hyperbolic Metamaterials

The future applications of hyperbolic metamaterials demand stacks of materials with alternative ultra-thin conductive/dielectric films with good homogeneity of the thickness and reduced roughness level. In this work, the technology of pulsed-DC magnetron sputtering of aluminum was optimized using the Taguchi method in order to fabricate Al films with improved roughness level. The performed structural characterization proved the smaller Al domains and better homogeneity of the surface. The optimized process was used to fabricate a multilayer structure of Al/HfOx as the metamaterial media. The fabricated structures were optically characterized in the UV/VIS range. The presented findings demonstrated the tunability effect of the effective reflectance of the examined stacks. The presented results are promising for the future application of multilayer structures in novel photonic devices based on hyperbolic metamaterials.

Gilbert Damping in Annealed Perpendicular Exchange Biased CoFeB/Pt/MnIr Multilayers

Exchange bias and intrinsic Gilbert damping [Formula: see text] are two important parameters in magnetic multilayers. To explore the correlation between exchange coupling and damping, the samples Ta (2.6[Formula: see text]nm)/Pt (2.5[Formula: see text]nm)/Co[Formula: see text]Fe[Formula: see text]B[Formula: see text] (0.63[Formula: see text]nm)/Pt (0.5[Formula: see text]nm)/Mn[Formula: see text]Ir[Formula: see text] ([Formula: see text])/Ta (4[Formula: see text]nm) are deposited by using pulsed-DC magnetron sputtering. The static and dynamic magnetic responses with different thickness of antiferromagnetic MnIr are investigated using vibrating sample magnetometer (VSM) and the pump-probe time-resolved magneto-optical Kerr effect (TR-MOKE). The exchange bias initially increases and then decreases with increasing thickness of MnIr layer, which is associated with the interfacial exchange coupling. The dynamic results demonstrate that the Gilbert damping of CoFeB/Pt/MnIr can increase by up to 40% compared with CoFeB/Pt. Based on the fact that the spin pumping has been excluded because of the Pt interlayer, we attribute the enhancement in Gilbert damping to the exchange coupling between AFM and FM.