Controlled Fabrication And Magnetic Properties Of In-plane C-axis Oriented BaM Films

With the rapid development of magnetic microwave devices towards miniature,planar and high-frequency,hexaferrite materials,especially in-plane c-axis oriented M-type hexaferrite(BaFe₁₂O₁₉,BaM)films,have received considerable interests owing to their unique self-biased properties.However,successful fabrication of these films has always been a challenge,and the commonly used pulsed laser deposition?PLD?and liquid phase epitaxy?LPE?methods are not feasible in industry-level application considering their large cost and less accessibility.In the present work,the in-plane c-axis oriented BaM films were fabricated by direct current?dc?magnetron sputtering,and a comprehensive investigation was conducted on film characterization to get an insight into the crystal structure,orientation relationship and microwave properties.A high-quality ceramic target is essential to the performance of the films prepared by dc magnetron sputtering.The effects of sintering atmosphere on the electrical and magnetic properties of BaM were initially studied,and it was found that argon is effective to lower the target's resistivity.While for the Z-type hexaferrite(Ba₃Co₂Fe₂₄O₄₁,Co₂Z),oxygen enriched sintering atmosphere was helpful in reducing the dielectric and magnetic losses of Co₂Z,and made it a promising candidate as microwave antenna substrate material.Highly c-axis in-plane aligned BaM films were then magnetron sputtered,exhibiting a large remanence ratio of 0.97 along easy axis and decent self-biased properties.The dependence of orientation and magnetic properties on various factors like sputtering power and atmosphere was investigated.The relieving effect of?-Fe₂O₃phase on the strains in the BaM films that originated from the film/substrate interface was analyzed.The discrepancy of the plate-like BaM grains and the inducing effect of the?-Fe₂O₃ secondary phase on the orientation of BaM film were investigated,using pole figures of multiple crystallographic planes.The lath-like structure model of the oriented BaM films was proposed,with the dislocations at the film/substrate interface releasing the strains inside BaM in?0001?plane,while in the plane that perpendicular to?0001?,grain boundaries played the significant role.In order to get micron-thick films,a layer-by-layer annealing procedure was designed,which successfully reduced the substrate-induced strains and allowed for the growth of thick?about 3.44?m?BaM films.The thick films demonstrated obvious in-plane anisotropy as indicated by X-ray diffraction patterns and polarized Raman spectra.The ferromagnetic resonance?FMR?frequency was 50.3 GHz at zero field,and increased linearly with the increasing external magnetic field.Considering the application in high-power microwave integrated devices,wide band-gap semiconductor substrate SiC was chose for the deposition of BaM films.The BaM films were sputtered on?11 2?0?plane of 6H-SiC substrates,with c-axis randomly distributed in the film plane,and exhibited spatial magnetocrystalline anisotropy,but an isotropy property in the film plane.The orientation relationship between BaM and 6H-SiC was comprehensively studied,and the inducing effect of the single crystal substrate on the orientation of the films was analyzed.