TY - GEN
T1 - Effect of film thickness on high frequency magnetic properties of polycrystalline Fe-Ga films
AU - Endo, Y.
AU - Sakai, T.
AU - Miyazaki, T.
AU - Shimada, Y.
N1 - Funding Information:
I. INTRODUCTION Fe-Ga alloys have been of much interest in electromagnetic devices such as stress sensors and actuators because of their moderate magnetostriction, relative low saturation field, and high tensile loading properties [1]. Recently, much attention has been focused on Fe-Ga films in the drive towards creating faster, smaller, and more energy efficient devices for information and communications technologies [2]. Therefore, Fe-Ga films have been widely studied from both fundamental and application points of view. Previous work on Fe-Ga films have been focused on the effect of Ga composition on magnetostriction, ferromagnetic resonance (FMR) frequency, and damping constant of these films [2],[3]. On the other hand, details about the effect of film thickness on these magnetic parameters of Fe-Ga films have not been understood fully. In particular, these magnetic properties of the films with thickness less than 20 nm have never been reported. Herein we evaluate high frequency magnetic properties of Fe-Ga films with thicknesses between 3 – 100 nm, and discuss in detail the effect of film thickness on the magnetic properties of these films. II. EXPERIMENTAL PROCEDURES Fe78Ga22 (Fe-Ga) films were deposited by DC magnetron sputtering onto glass substrates. During film deposition, a magnetic field of 47.8 kA/m approximately was applied to the film plane to induce uniaxial anisotropy. The thickness of Fe-Ga films varied from 3 nm to 100 nm. The films were capped with a 10-nm thick Cu layer to prevent oxidation. The composition of the film was determined by energy dispersive x-ray spectroscopy (EDX). Transmission electron microscope (TEM) was employed to characterize the crystallographic structure of Fe-Ga films. As for magnetic properties of the films, the in-plane M-H curves were measured by VSM. The damping constants (α) of films were evaluated by the FMR spectra using the coplanar waveguide (CPW) and the vector network analyzer (VNA). The measurement of magnetostriction was performed using a Thin-film Magnetostriction Measurement System (Toei Scientific Industrial Co., Ltd) which utilizes an optical-cantilever method to detect the sample deflection caused by magnetostrictive effect. Saturation magnetostriction (λs) of the film was evaluated using this system in an external magnetic field of 0.0 - +13.5 kA/m, which is strong enough to magnetically saturate the films. These measurements were performed at room temperature. III. RESULTS AND DISCUSSION Figure 1 shows the selected-area diffraction (SAD) patterns of the 100-nm thick Fe-Ga film as an example. (110), (200), (211), and (220) diffraction rings caused by a single bcc Fe-Ga phase can be observed. Note that no trace of diffraction rings of any other possible phases, such as nitride and oxide, was detected for any samples. On the basis of these results, it is pointed out that the single Fe-Ga phase remains unchanged regardless of the film thickness. The magnetization curve of the Fe-Ga film is dependent of the film thickness: a weak uniaxial magnetic anisotropy can be observed in the thickness range less than 5 nm, while the isotropic magnetization appears in the thickness range above 5 nm. This result suggests that the magnetic softness is significantly affected by the film thickness. Figure 2 shows the thickness dependence of saturation magne-tostricition (λs) and damping constant (α) for the Fe-Ga films. λs increases markedly from 15 ppm to 24 ppm in the thickness range up to 30 nm, and then decreases to 18 ppm in the thickness range above 30 nm. All values becomes lower than the bulk isotropic polycrystalline value (98 ppm). On the other hand, α increases markedly from approximately 0.015 to 0.081 as the film thickness is varied from 3 to 20 nm. α maximizes in the thickness of 30 nm and its value is approximately 0.084. Furthermore, in the thickness range above 30 nm, α decreases to 0.068 as the film thickness increases. All values are much larger than that of a single crystal Fe-Ga film [2], indicating that the extrinsic damping overlaps with the intrinsic damping. These results suggest that structural and/or magnetic inhomogeneities strongly influence λs and α regardless of the film thickness. ACKNOWLEDGEMENT This work was supported in part by JSPS KAKENHI Grant Number JP26289082 from MEXT, Japan. This work was supported in part by CIES collaborative research from CIES, Tohoku University. This work was also supported in part by the Murata Science Foundation and ASRC in Japan.
Publisher Copyright:
© 2017 IEEE.
PY - 2017/8/10
Y1 - 2017/8/10
N2 - Fe-Ga alloys have been of much interest in electromagnetic devices such as stress sensors and actuators because of their moderate magnetostriction, relative low saturation field, and high tensile loading properties [1].
AB - Fe-Ga alloys have been of much interest in electromagnetic devices such as stress sensors and actuators because of their moderate magnetostriction, relative low saturation field, and high tensile loading properties [1].
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U2 - 10.1109/INTMAG.2017.8007909
DO - 10.1109/INTMAG.2017.8007909
M3 - Conference contribution
AN - SCOPUS:85034658194
T3 - 2017 IEEE International Magnetics Conference, INTERMAG 2017
BT - 2017 IEEE International Magnetics Conference, INTERMAG 2017
PB - Institute of Electrical and Electronics Engineers Inc.
T2 - 2017 IEEE International Magnetics Conference, INTERMAG 2017
Y2 - 24 April 2017 through 28 April 2017
ER -