Thin Films of BaM Hexaferrite with an Inclined Orientation of the Easy Magnetization Axis: Crystal Structure and Magnetic Properties

Thin (~50 nm thick) BaM hexaferrite (BaFe₁₂O₁₉) films were grown on (1-102) and (0001) cut α-Al₂O₃ (sapphire) substrates via laser molecular beam epitaxy using a one- or two-stage growth protocol. The advantages of a two-stage protocol are shown. The surface morphology, structural and magnetic properties of films were studied using atomic force microscopy, reflected high-energy electron diffraction, three-dimensional X-ray diffraction reciprocal space mapping, powder X-ray diffraction, magneto-optical, and magnetometric methods. Annealed BaFe₁₂O₁₉/Al₂O₃ (1-102) structures consist of close-packed islands epitaxially bonded to the substrate. The hexagonal crystallographic axis and the easy axis (EA) of the magnetization of the films are deflected from the normal to the film by an angle of <i>φ</i>~60°. The films exhibit magnetic hysteresis loops for both in-plane <b>H</b>_in-plane and out-of-plane <b>H</b>_out-of-plane magnetic fields. The shape of <i>M</i>_out-of-plane(<i>H</i>_in-plane) and <i>M</i>_in-plane(<i>H</i>_in-plane) hysteresis loops strongly depends on the azimuth <i>θ</i> of the <b>H</b>_{in plane}, confirming the tilted orientation of the EA. The <i>M</i>_out-of-plane(<i>H</i>_out-of-plane) magnetization curves are caused by the reversible rotation of magnetization and irreversible magnetization jumps associated with the appearance and motion of domain walls. In the absence of a magnetic field, the magnetization is oriented at an angle close to <i>φ</i>.