Nano-magetic thin films are intensively researched in the field of ultrahigh-density magnetic or magnetooptical recordings and microwave absorption material. Hexagonal ferrite thin films are of great interest as potential media for magnetic recording material and microwave absorbers in the field of aeronautics and astronautics. They possess high magnetic loss tangent, coercive force and saturation magnetization, good mechanical rigidity and chemical stability, and huge uniaxial magnetic anisotropy. The present study is an attempt to demonstrate the feasibility of producing high quality Rare-earth doped Sr-ferrite films by sol-gel method and to explore the relation between crystal quality, magnetic properties and microwave absorption properties. Finally we succeed increasing magnetic properties of Sr-ferrite films by doping La ,Ce or Nd ,and improving the films microwave absorption properties by doping La or Ce.

Ln-doped nano-strontium ferrite films, SrLn_xFe_12-xO₁₉(Ln included La, Ce and Nd) (x=0,0.2…1.0), were prepared firstly from metal nitrates and citric by the citrate sol-gel method for the precursor, secondly depositing on SiO₂ substrate. The phase composition and microstructure of the SrLn_xFe_12-xO₁₉ films were characterized by X-ray Diffraction Analysis (XRD), Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscopy (AFM). The quantitative compositional analysis of the films was measured by X-ray energy dispersive analysis (EDS). The complex permittivity and complex permeability which characterized microwave absorption properties of the films were measured by Microwave Vector Network Analyzer. The magnetic properties were measured by Vibrating Sample Magnetometer (VSM).In the research the three doped strontium ferrite films were compared and analyzed in the magnetic and microwave absorption properties.

Results showed that: (1) the rare-earth ions completely entered into the strontium ferrite lattice, and the doped element did not change the strontium ferrite appearance. The grain size of rare-earth doped strontium ferrite films was approximately 40nm-80nm, length of it was 100nm; (2) The magnetoplumbite structure of strontium ferrite was proved through testing a concertina form of the crystal grain by AFM analyzer; (3) the maximum coercivity (Hc) of SrLn_xFe_12-xO₁₉ films (Ln were La, Ce and Nd respectively) was 476.59 kA/m, 494.07 kA/m and 505.73 kA/m at x=0.2; (4) the La doped films possessed a wider microwave absorption frequency range with better gross loss angle tangent from 9GHz to 10.5GHz, and the gross loss angle tangent of SrLa_0.2Fe_11.8O₁₉ arrived the maximum value 0.2709; otherwise the Ce doped films had a more excellent microwave absorption property than the La doped in the frequency range of 11.5GHz-12GHz.

Keywords: Nano-Strontium films ; Rare-earth doped; Microwave absorption properties; Magnetic properties