High Frequency Characteristics and Electrical Properties of Multilayer FeCoHfO/AlOx Films

For the high frequency application in mobile communication technology, the operating frequency is over 3GHz, hence the ferromagnetic resonance frequency (fres) of magnetic films must be over 3 GHz. In this study, FeCoHfO alloy is chosen as a promising material system for this application. Inserting an insulator (e.g., AlOx) layer into ferromagnetic layers is a good way to enhance the resistivity and therefore to reduce the eddy current loss. A significant reduction of hard axis anisotropic field was observed when the number of multilayer reached five. With this optimum condition of [FeCoHfO (400 nm)/AlOx (10 nm)]3, favorable magnetic properties (effective anisotropy field of 110 Oe), high frequency characteristics (permeability ∼ 100 at 100 MHz and ferromagnetic resonance frequency over 3 GHz) and high electrical resistivity ρ ∼ 1074 μΩcm were obtained.