Magnetron Sputtered Perpendicular Barium Hexaferrite Thin Films Produced by the Multilayered Method

Abstract

We report on the synthesis and characterization of thin M-type barium hexaferrite (BaFe₁₂O₁₉ or BaM) films on sapphire (0001) substrates by RF magnetron sputtering. Single layers of 150 nm, 200 nm (S₂₀₀), 400 nm (S₄₀₀), 600 nm, and 700 nm were fabricated. Multilayered technique with inner-layer annealing was employed to fabricate the 400 nm (M₄₀₀) BaM films. The thickness dependence of the magnetic, structural, elemental analysis, and surface morphological properties of the BaM films has been investigated using VSM, XRD, EDX, and SEM, respectively. For the M₄₀₀ BaM films, excellent magnetic properties with high values of out-of-plane coercivity (H_c┴ = 3.1 KOe) and squareness (S_┴ = 0.9) were obtained. The surface morphology of the M₄₀₀ shows a platelet-like grains, which have their c-axis orientation in the out-of-plane direction. The magnetic properties and XRD data of the S₂₀₀ films and M₄₀₀ were about the same. For the single S₄₀₀, S₆₀₀, and S₇₀₀ films, the magnetic properties have been reduced due to the excess oxygen concentration and the exchange interactions, the stress relaxation of the lattice constant, and the formation of the acicular grains. The acicular grains of the S₄₀₀ films favor their c-axis aligned in the in-plane direction.