Microstructure and magnetic properties of FeCoHfN thin films deposited by DC reactive sputtering.

• The introduction of nitrogen can effectively refine the grain size of FeCoHfN films. • Amorphization and the enrichment of HfN improve the high-frequency magnetic properties of the films. • Appropriate nitrogen pressure plays a key role in forming favorable microstructure and phase composition. • The transition of nanocrystalline-amorphous structure can be realized by adjusting the N element. • The film deposited at R (N 2) = 12% exhibits a high 4π M s of 16.2 kGs, a great initial μ of 293, and a high f r of 2.97 GHz. The microstructure and electro-magnetic properties of FeCoHfN thin films deposited by reactive sputtering under an in-situ magnetic field have been studied as a function of nitrogen partial pressure (R (N 2)). As the (R (N 2)) increases, the grain size of α-FeCo phase can be effectively reduced, and the structure of the films changes from an amorphous/nanocrystalline dual-phase structure with ultrafine α-FeCo magnetic nanoparticles isolated by a nonmagnetic insulating layer to a single amorphous structure. The structural transformation and the enrichment of HfN layer improve the resistivity and static and dynamic soft magnetic properties of the films. Higher resistivity is expected to reduce eddy current losses at high frequencies. The critical (R (N 2)) when the film shows indications of excellent high-frequency magnetic properties is 8%. The deposited FeCoHfN thin films have high saturation magnetization of 14.9–16.2 kGs, great permeability of 222–322 at GHz, and high ferromagnetic resonance frequency up to 3.5 GHz, showing the promise of high-frequency applications. [ABSTRACT FROM AUTHOR]