Structure And Magnetic Properties Of FeCoNd Nano-magnetic Thin Films

With the miniaturization and high frequency technology of electromagnetic devices, the soft magnetic properties of the materials are put forward higher requirements. The soft magnetic materials with high permeability (μ), high saturation magnetization Ms, high resistivity p and the in-plane uniaxial anisotropy field (Hk) fall under the people's attention and become a active area of research. FeCo-based soft magnetic thin films become a research hotspot due to their high permeability, high saturation magnetization and the broadband range of high permeability characteristics. The high frequency soft magnetic properties of Co-based amorphous thin films can be improved by the rare-earth elements doping.A series of magnetic FeCoNd thin films in this work were deposited by radio frequency (RF) magnetron co-sputtering onto Si (111) substrates by changing the experimental parameters. The microstructure and the crystal structure of the films were examined using FEI Tacnai G2 F30 transmission electron microscopy (TEM) and X-ray diffraction (XRD) with Cu-Ka radiation, respectively. Energy dispersive spectroscopy (EDS) was used to determine the composition of the films. Surface topographies were observed with an atomic force microscope (AFM), and the domain structure at the surface was studied using magnetic force microscopy (MFM) with soft magnetic tips magnetized perpendicular to the sample plane. The static magnetic properties of FeCoNd films were measured by vibrating sample magnetometer (VSM). The high-frequency characteristics of the samples were obtained by using the shorted microstrip transmission-line perturbation method. The main contents are briefly introduced as follows:Ⅰ. The sample prepared at room temperature:Amorphous FeCoNd thin films have been prepared using RF co-sputtering at room temperature. Their magnetic properties are strongly dependent upon the thickness of films. When the thickness is higher than a critical value, i.e. tc, a stripe domain pattern will be observed due to the existence of strong perpendicular magnetic anisotropy. The occurrence of perpendicular anisotropy is suggested to originate from columnar structure with columns perpendicular to the film plane. On the contrary, reducing the thickness below tc, a well in-plane uniaxial magnetic anisotropic behavior and favorable soft magnetic properties are achieved.Ⅱ. The sample dealt with vacuum magnetic field heat treatments.The FeCoNd films with a stripe domain pattern prepared at room temperature were dealt with 300,400,500,600,700,800℃vacuum magnetic field heat treatment in order to improving their micro-structure and magnetic properties. Stripe domain can be eliminated by 400 and 500℃heat treatment, so that the magnetic moment lying in the film plane, with in-plane uniaxial anisotropy. The microwave magnetic permeability reveals two major resonance peaks for the samples after 300,600,700, 800℃heat treatment. The first peak is due to the domain-wall resonance, and the second peak arises from the natural resonance.