Magnetic property and stress study of barium hexaferrite thin films with different structures

M-type barium hexaferrite (BaM) thin films with different structures (ds100: single-layer 100 nm thick film; ds200: single-layer 200 nm thick film; db200: bilayer 200 nm thick film, where the thickness of each layer is 100 nm and the total film thickness is 200 nm) were deposited on (001) sapphire (Al2O3) substrate by radio frequency (RF) magnetron sputtering. Effects of different structures on the crystallographic, morphological, magnetic properties and stress were investigated in details. For the structure of ds100, BaM film processes platelet-like grains, which shows excellent magnetocrystalline anisotropy and large squareness ratio S⊥ (0.62). For the structure of ds200, there are a lot of acicular grains. Thus, the c-axis in-plane oriented and/or randomly oriented grains induce poor magnetocrystalline anisotropy. For the structure of db200, the platelet-like grains dominate the microstructure. Both squareness ratio S⊥ (0.67) and coercivity Hc⊥ (98.6 kA/m) of the db200 show the highest values among the three kinds of the film structures. In addition, with the increase of film thickness from 100 nm to 200 nm, the stress in film decreases gradually. Compared with the other structures, the bilayer 200 nm thick film (db200) obtains the smallest stress.