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42ISSN 2072-5981
Volume 17, Issue 2 Paper No 15205, 1-4 pages 2015
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August 2, 1996 First Issue was appeared at July 25, 1997
© Kazan Federal University (KFU)*
"Magnetic Resonance in Solids. Electronic Journal" (MRSey) is a
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Editors-in-Chief Jean Jeener (Universite Libre de Bruxelles, Brussels) Boris Kochelaev (KFU, Kazan) Raymond Orbach (University of California, Riverside)
Executive Editor Yurii Proshin (KFU, Kazan) [email protected]
Editors
Vadim Atsarkin (Institute of Radio Engineering and Electronics, Moscow) Yurij Bunkov (CNRS, Grenoble) Mikhail Eremin (KFU, Kazan) David Fushman (University of Maryland,
College Park)
Hugo Keller (University of Zürich, Zürich) Yoshio Kitaoka (Osaka University, Osaka) Boris Malkin (KFU, Kazan) Alexander Shengelaya (Tbilisi State University, Tbilisi) Jörg Sichelschmidt (Max Planck Institute for Chemical Physics of Solids, Dresden) Haruhiko Suzuki (Kanazawa University,
Kanazava) Murat Tagirov (KFU, Kazan) Dmitrii Tayurskii (KFU, Kazan) Valentin Zhikharev (KNRTU, Kazan)
In Kazan University the Electron Paramagnetic Resonance (EPR) was discovered by Zavoisky E.K. in 1944.
*
Nonlinear FMR spectra in yttrium iron garnet
Yu.M. Bunkov1'2, P.M. Vetoshko3, I.G. Motygullin1, T.R. Safin1, M.S. Tagirov1, N.A. Tukmakova1'* 1 Kazan Federal University, Kremlevskaya 18, 420008 Kazan, Russia 2Institut Neel, CNRS et Universite Joseph Fourier, F-38042 Grenoble, France 3Institute of Radio Engineering and Electronics, RAS, 125009, Moscow, Russia * E-mail: nadejdatukmakova@yandex. ru
(Received December 15, 2015; revised December 22, 2015; accepted December 25, 2015)
Results of demagnetizing effect studies in yttrium iron garnet YsFesOj^ thin films are reported. Experiments were performed on X-Band of electron paramagnetic resonance spectrometer at room temperature. The ferromagnetic resonance (FMR) spectra were obtained for one-layer single crystal YIG films for different values of the applied microwave power. Nonlinear FMR spectra transformation by the microwave power increasing in various directions of magnetic field sweep was observed. It is explained by the influence of the demagnetization action of nonequilibrium magnons.
PACS: 76.30.-v, 74.25.nj, 75.50.Gg Keywords: yttrium iron garnet, EPR, magnons
The FMR spectra investigations of yttrium iron garnet (YIG) Y3Fe5O12 single crystal thin films are presented. Experiments were performed on X-band of electron paramagnetic resonance (EPR) spectrometer Varian E-12 (f & 9.3 GHz) at room temperature. The sample was prepared in Carat company (Lvov, Ukraine) by standard isothermal liquid phase epitaxial (LPE) method during the joint work with the RAS Institute of Kotelnikov Radio Engineering and Electronics [1]. The yttrium iron garnet is a well-studied crystal with a ferrimagnetic ordering (Tc = 560 K). The 2D gadolinium gallium garnet (460 ^ 490 ^m) was used as a substrate for the thin film (6 ^ 9 ^m) of yttrium iron garnet. The typical FMR spectrum in the perpendicular orientation of the external magnetic field H to the surface is shown in Fig. 1a. The experiments were performed at the microwave pump power P of 10 mW, modulation amplitude of 5 mOe. Fig. 1b shows the corresponding integrated spectrum. The integrated spectra are presented in Fig. 2a and 2b.
The characteristic "collapse" points in all spectra can be seen. These points correspond to such value of a magnetic field, where the sharp decrease of adsorption is observed. With the increasing of microwave pumping power P the position of "collapse" H0 shifts to the lower fields. This shift depends linearly on the microwave pumping power (see Fig. 3a). Furthermore, the spectra strongly depend on the field sweep direction (Fig. 3b).
Fig. 3 shows integrated spectra for the various microwave power values in different directions of the magnetic field sweep.
The non-linearity of FMR spectra corresponds to the big value of magnetization deflection angle and decreased demagnetization factor. This effect is clearly seen in the Fig. 2, where the FMR lines at small excitations show the inhomogeneous broadening. With the increasing of
^This paper material was selected at XVIII International Youth Scientific School "Actual problems of magnetic resonance and its application", Kazan, 26 - 30 October 2015. The paper was recommended to publication in our journal and it is published after additional MRSej reviewing.
25
20
15
10
V. . .
3975
4000
4025
H (Oe)
4050
4075
25 20 15 10 5 0 -5
; ) " ft»'
3975
4000 4025 H (Oe)
4050
4075
Figure 1. The differential FMR spectrum of YIG thin film in perpendicular orientation of magnetic field to the surface (a) and corresponding integrated spectrum (b).
Decreasing of magnetic field )
4025
4030 4035
H(Oe)
4040
4040
Figure 2. Integrated spectra for various microwave power P in increasing (a) and decreasing (b) of magnetic field.
4035
4030
O
a
4025 -
40
35 30 25 3 20
CIS
M 15 10 5 0
1 ■
; 30 mW V ) ;
\ Decreasing of
V^magnetic field -
V\ Increasing of
: r \\ magnetic field -
4020
4025
4030 H (Oe)
4035
4040
Figure 3.
for various
The dependence of the collapse position from the microwave pump power (a); FMR spectra direction of magnetic field sweep (b).
Yu.M. Bunkov, P.M. Vetoshko, I.G. Motygullin, et al.
excitation the line asymmetry is observed. This asymmetry can be explained by a relatively large angle of magnetization deflection (, which decreases the demagnetization field 4nMs cos ( and, consequently, increases the frequency of FMR at given field [2]:
Wres = Y(Ho - 4nMs cos (). (1)
The creation of magnon leads to a reducing the sample magnetization Ms to one Bohr magneton (3m. The number of stationary nonequilibrium magnons Nm is proportional to the absorption and microwave power. As a result the signal shifts to the lower field:
AHo = 4nAMs cos 3, (2)
where AMs = NM(3M. The excited state has a relaxation rate. At some magnetic field H0 value the signal disappears ("collapse" points). It can be explained as the microwave pumping power is not enough for supporting the necessary amount of nonequilibrium magnons Nm . In Fig. 2 and Fig. 3 the signal shift from the resonance is seen, which is described in good agreement with equations (1) and (2). The described FMR spectrum behavior was simulated. The results of simulation are shown in Fig. 4 and Fig. 5, AP = AH0, where P is a microwave power, A is a dimensional coefficient.
It is clearly seen an excellent match of simulated spectrum transformation with experimental behavior, but for the total understanding of all nonlinear effects and, consequently, for suggestion of theoretical model it is necessary to provide some additional investigations of magnons dynamics.
AH (Oe) AH (Oe)
Figure 4. Simulated FMR spectra.
AH (Oe)
Figure 5. Simulated FMR spectra at the different magnetic field sweep directions (AP = 30).
Acknowledgments
The work is performed according to the Russian Government Program of Competitive Growth of Kazan Federal University. The work of P.M. Vetoshko is supported by RSF grant No.14-22-00279.
References
1. Syvorotka 1.1., Vetoshko P. M., Skidanov V. A., Shavrov V. G., Syvorotka I. M., IEEE Trans. Magn. 51, 7029234 (2015).
2. Gurevich A. G., Melkov G. A., Magnetization Oscillations and Waves (CRC Press, 1996).
