TY - JOUR
T1 - Brillouin light scattering from magnetic excitations in superparamagnetic and ferromagnetic Co–Al–O Granular films
AU - Yoshihara, Akira
AU - Maeda, Toshiteru
AU - Kawamura, Satoshi
AU - Nakamura, Shintaro
AU - Nojima, Tsutomu
AU - Takeda, Yoshihiko
AU - Ohnuma, Shigehiro
N1 - Funding Information:
The authors sincerely thank the late Emeritus Professor Hiroyasu Fujimori of Tohoku University for his interest and encouragement throughout this study. This work was supported by a Grant-in-Aid for Scientific Research (No. 23560027) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Funding Information:
Acknowledgements The authors sincerely thank the late Emeritus Professor Hiroyasu Fujimori of Tohoku University for his interest and encouragement throughout this study. This work was supported by a Grant-in-Aid for Scientific Research (No. 23560027) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Publisher Copyright:
© 2018 The Physical Society of Japan.
PY - 2018
Y1 - 2018
N2 - A systematic study of Brillouin light scattering (BLS) from superparamagnetic (SPM) and ferromagnetic (FM) Co–Al–O granular films was performed under magnetic fields of up to 4.6 kOe in the standard backscattering geometry at room temperature. The SPM and FM boundary, defined as the Co composition at which the exchange field vanishes, was found to be located at xC(Co) = 59.3 ± 1.3 at. %. From FM films we observed a pair of bulk spin-wave peaks on both the positive- and negative-frequency sides and a surface localized Damon–Eshbach peak only on the positive-frequency side under the present scattering conditions. From SPM films, a pair of broader but propagative excitation peaks with asymmetric intensity were observed on both frequency sides in a spectrum. We performed a numerical analysis of the BLS spectrum by employing the theory developed by Camley and Mills (CM) while retaining dipole and exchange couplings for FM films and only dipole coupling for SPM films. The CM theory successfully reproduced the observed spectrum for both SPM and FM films. The SPM spectrum exhibits a singlet–doublet peak structure similarly to an FM SW spectrum. The SPM peak stems from the dipole-coupled larger-amplitude precession motion of the granule magnetic moment around the external-field-induced magnetization.
AB - A systematic study of Brillouin light scattering (BLS) from superparamagnetic (SPM) and ferromagnetic (FM) Co–Al–O granular films was performed under magnetic fields of up to 4.6 kOe in the standard backscattering geometry at room temperature. The SPM and FM boundary, defined as the Co composition at which the exchange field vanishes, was found to be located at xC(Co) = 59.3 ± 1.3 at. %. From FM films we observed a pair of bulk spin-wave peaks on both the positive- and negative-frequency sides and a surface localized Damon–Eshbach peak only on the positive-frequency side under the present scattering conditions. From SPM films, a pair of broader but propagative excitation peaks with asymmetric intensity were observed on both frequency sides in a spectrum. We performed a numerical analysis of the BLS spectrum by employing the theory developed by Camley and Mills (CM) while retaining dipole and exchange couplings for FM films and only dipole coupling for SPM films. The CM theory successfully reproduced the observed spectrum for both SPM and FM films. The SPM spectrum exhibits a singlet–doublet peak structure similarly to an FM SW spectrum. The SPM peak stems from the dipole-coupled larger-amplitude precession motion of the granule magnetic moment around the external-field-induced magnetization.
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U2 - 10.7566/JPSJ.87.044707
DO - 10.7566/JPSJ.87.044707
M3 - Article
AN - SCOPUS:85043691888
SN - 0031-9015
VL - 87
JO - Journal of the Physical Society of Japan
JF - Journal of the Physical Society of Japan
IS - 4
M1 - 044707
ER -