Orientation Growth and Magnetic Properties of BaM Hexaferrite Films Deposited by Direct Current Magnetron Sputtering

Abstract

In‐plane c‐axis oriented Ba‐hexaferrite (BaM) thin films were prepared on a‐plane (112¯0) sapphire (Al2O3) substrates using direct current (DC) magnetron sputtering followed by ex‐situ annealing. The sputtering atmosphere was found to have a great influence on the stoichiometry, orientation growth, and grain morphology of the as‐prepared BaM films. With moderate oxygen partial pressure during sputtering, in‐plane c‐axis highly oriented BaM films were obtained. The films showed strong magnetic anisotropy with a high hysteresis loop squareness (Mr/Ms of 0.96) along in‐plane easy axis and a low Mr/Ms of 0.05 along in‐plane hard axis. Rocking curves and pole figures were utilized to reveal the epitaxial‐like orientation relationship of the BaM films relative to the sapphire substrates, as well as the orientation growth dispersion of the hexagonal platelet‐shaped grains in BaM films.

Epitaxially grown BaM hexaferrite films having uniaxial axis in the film plane for self-biased devices

“…1(b) shows the rocking curves of the peak of the 3.44-μm-thick BaM film that was measured along two mutually orthogonal directions: Φ = 0° and Φ = 90°. Compared with Φ = 90°, the Φ = 0° peak is noticeably wider, which is caused by the small grain size along c -axis 39 .…”

“…All the samples, except the thinnest one, show an obvious in-plane c -axis orientation with two main peaks being indexed to the and planes of BaM. The α -Fe 2 O 3 phase is also detected in the films owing to its higher thermodynamic stability than BaM and tendency of persisting during BaM fabrication 38 39 45 . Our previous studies have shown that α -Fe 2 O 3 phase plays a significant role in promoting the in-plane c -axis oriented growth of the BaM films on sapphire substrates 38 39 , and acts as a temporary template during the orientation growth of the BaM crystallites 20 .…”

“…The α -Fe 2 O 3 phase is also detected in the films owing to its higher thermodynamic stability than BaM and tendency of persisting during BaM fabrication383945. Our previous studies have shown that α -Fe 2 O 3 phase plays a significant role in promoting the in-plane c -axis oriented growth of the BaM films on sapphire substrates3839, and acts as a temporary template during the orientation growth of the BaM crystallites20. Two small peaks corresponding to and crystallographic planes of BaM also appear in the XRD patterns.…”

“…3 . All the samples, except the thinnest one, are composed of parallel aligned grains, indicating in-plane orientation of c -axis 38 39 . The surface morphology of the 45-nm-thick sample, as shown in Fig.…”

“…Specifically, direct current (DC) magnetron sputtering has long been used to sputter metal materials, while oxide ceramics have always been prepared by RF magnetron sputtering, which is subject to low sputtering rate compared with DC sputtering. In our previous studies, however, well aligned in-plane c -axis oriented BaM thin films (∼120 nm in thickness) were successfully prepared using DC magnetron sputtering 38 39 . In the present work, using seed layers and a layer-by-layer annealing procedure, we obtained 3.44-μm-thick epitaxially grown BaM films that hold promise for various microwave applications.…”