TY - GEN
T1 - Change in the magnetization dynamics of Fe1-xCox thin films with Co concentration x
AU - Endo, Y.
AU - Miyazaki, T.
AU - Shimada, Y.
N1 - Funding Information:
I. INTRODUCTION The magnetization dynamics in magnetic thin films have been of much interest in magnetic devices such as magnetic recording heads, media, and magnetic random access memories. One of the most dominant parameters in understanding magnetization dynamics is the Gilbert damping constant (α), which describes the strength of damping torque in magnetic thin films. However, details about the behavior of α in a magnetic thin film are not understood fully. In addition, there are few experimental reports about the effect of other magnetic parameters such as magnetic anisotropy and saturation magnetostriction (λs) on α in a magnetic thin film [1]. Until now, we have reported a correlation between α and λs in Ni-Fe binary alloy films and found different behaviors of α depending on positive or negative values of λs [2]. Herein, we choose Fe-Co with high saturation magnetization as magnetic materials, evaluate magnetization dynamics of Fe-Co thin films and discuss in detail the effect of Co concentration on damping constant in these thin films. II. EXPERIMENTAL PROCEDURES 10-nm thick Fe1-xCox films were deposited by DC magnetron sputtering onto glass substrates. The Co concentration (x) was adjusted by controlling the number of Co chips placed on the Fe0.70Co0.30 target. Coplanar waveguides (CPWs) composed of a trilayer structure of Cr (5 nm)/Cu (300 nm)/Cr (5 nm) were fabricated on glass substrates (relative permittivity; εr=7.0) by photo-beam lithography, DC magnetron sputtering, and a lift-off technique. The signal line, gap, and ground line widths were 50, 12, and 88 μm, respectively, which provided a characteristic impedance (Z0) for the CPW of 50 Ω. The concentration of Fe1-xCox films was evaluated by energy dispersive x-ray spectroscopy (EDX), while transmission electron microscope (TEM) was employed to characterize the crystallographic structure of Fe-Co films. As for magnetic properties of the films, the in-plane magnetization (M-H) curves were measured by VSM. The damping constants (α) of films were evaluated by the ferromagnetic resonance (FMR) spectra using the CPW and the vector network analyzer (VNA). These measurements were performed at room temperature. III. RESULTS AND DISCUSSION As for the crystallographic structure of 10-nm-thick Fe1-xCox films, TEM images of these films indicate that a single bcc Fe-Co phase remains unchanged regardless of Co concentrations (x). Note that no trace of diffraction rings of any other possible phases, such as nitride and oxide, was detected for any samples. Figure 1 shows changes in the saturation magnetization (4πMs) and the saturation field (Hs) of 10-nm thick Fe1-xCox films with Co concentration (x). 4πMs slightly increases as x increases up to 0.40, slightly decreases for x = 0.45, and finally decreases for x = 0.50. This behavior is similar to that of bulk Fe-Co binary alloy. Hs slightly increases and decreases in the range of x below 0.40, and markedly increases for x above 0.40. Figure 2 shows damping constant (α) as a function of Co concentration (x) for 10-nm thick Fe1-xCox films. α depends on x: α slightly increases from 0.012 to 0.015 and then keeps almost constant as x increases up to 0.40. For x = 0.45, α maximizes and its value is approximately 0.039. Moreover, α decreases to 0.033 as x becomes 0.50. These behaviors are similar to the change in the effective magnetic energy (Ms*Hk/2)eff with x as noticed in Fig. 2, and are nearly the same as the change in the magnetostriction of bulk Fe-Co alloy with x [3]. Therefore, these behaviors suggest that the dipole-dipole interaction between adjacent spins play an important role for the magnetization dynamics of thin Fe-Co binary alloy film. ACKNOWLEDGEMENT The authors would like to thank Prof. Osamu Kitakami, Associate Prof. Satoshi Okamoto, Assistant Prof. Nobuaki Kikuchi at Tohoku University for performing the photo lithography. 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.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2017/8/10
Y1 - 2017/8/10
N2 - The magnetization dynamics in magnetic thin films have been of much interest in magnetic devices such as magnetic recording heads, media, and magnetic random access memories.
AB - The magnetization dynamics in magnetic thin films have been of much interest in magnetic devices such as magnetic recording heads, media, and magnetic random access memories.
UR - http://www.scopus.com/inward/record.url?scp=85034650193&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85034650193&partnerID=8YFLogxK
U2 - 10.1109/INTMAG.2017.8007658
DO - 10.1109/INTMAG.2017.8007658
M3 - Conference contribution
AN - SCOPUS:85034650193
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 -