Physical properties of Al doped Ba hexagonal ferrite thin films

Published

January 22, 2013

Author(s)

Harward Ian, Yan Nie, Daming Chen, Josh Baptist, Justin Shaw, Eva J. Liskova, Stefan Visnovsky, Petr Siroky, Michal Lesnak, Jaromir Pistora, Zbigniew Celinski

Abstract

We developed the thin film microwave magnetic material, M-type barium hexagonal ferrite (BaM) doped with Al, for signal processing devices operating above 40 GHz with little to no applied magnetic field. Al was chosen as the dopant material because it significantly increases the already strong anisotropy field of BaM. A series of thin film BaAl_xFe_12-xO₁₉ samples, x ranging from 0 to 2 in 0.25 steps, were deposited on Pt templates using a metal-organic decomposition growth technique. The resulting films are polycrystalline and highly textured, with the hexagonal c-axis directed out of plane. These films are also self-biasing; easy axis hysteresis loops have a high squareness ratio, i}s, in the 0.83-0.92 range. As expected, the anisotropy field increases with x, ranging from 1.34 to 2.19 x 10⁶ A/m (16.9-27.5 kOe) for (I}x=0-2, while the saturation magnetization M_s decreases with x, ranging from 0.334 to 0.175 x 10₆ A/m (4πM_s = 4.2-2.2 kG) for x=0-2. These values were measured at room temperature, but the temperature dependence of these quantities was also measured below room temperature, down to 30 K. The measured ferromagnetic resonance linewidths, on the order of 12-30 x 10³ A/m (140-370 Oe) for compositions below x=1, indicate device-quality films. Above a certain threshold, the linewidth increases linearly with frequency at a rate of 0.2-0.64 x 10³ (A/m)/GHz (2.5-8 Oe/GHz) for x=0-1, respectively. The behavior of the linewidth is correlated with the structural properties of the films measured using x-ray diffraction and atomic force microscopy. The results of magnetic force microscopy, Curie point measurements, spectral ellipsometry (index of refraction), and magneto-optical measurements are also included and discussed.

Citation

Journal of Applied Physics

Volume

113

Issue

043903

Pub Type

Journals

Citation

Ian, H. , Nie, Y. , Chen, D. , Baptist, J. , Shaw, J. , Liskova, E. , Visnovsky, S. , Siroky, P. , Lesnak, M. , Pistora, J. and Celinski, Z. (2013), Physical properties of Al doped Ba hexagonal ferrite thin films, Journal of Applied Physics (Accessed October 10, 2025)