TY - GEN
T1 - Magnetization dynamics of post-annealed yttrium-iron-garnet thinfilms sputter deposited over a platinum electrode
AU - Pati, S.
AU - Al-Mahdawi, M.
AU - Shiokawa, Y.
AU - Sahashi, Masashi
AU - Endo, Y.
N1 - Funding Information:
Recently, yttrium iron garnet (YIG, Y3Fe5O12) has been proved to be an efficient material for magnonics and spintronics application after discovery of spin pumping , spin seebeck effect  and spin hall magnetoresistance  phenomena. Being a magnetic insulator, YIG often considered as the best medium for spin-wave propagation due to its very small intrinsic damping coefficient in bulk ~3×10-5. However, for device application, it is required to fabricateYIG thin films over a metallic electrode without affecting its damping coefficient. Garnet films have been fabricated by various techniques, including liquid-phase epitaxy (LPE), pulsed laser deposition (PLD), radio frequency (rf) magnetron sputtering, chemical vapor deposition, etc. However, the control of composition of multi component oxide like YIG is difficult. In this study, we report the dynamic magnetic properties of post-annealed YIG amorphous films deposited over platinum electrode by rf magnetron sputtering. Amorphous YIG films with several thicknesses (20, 50, 100, and 400 nm) were deposited on Al2O3 (0001) substrate with and without a 25-nm thick Pt buffer layer by rf magnetron sputtering at room temperature. Pt buffer layer was fabricated by dc magnetron sputtering operated at 30 watt in room temperature. YIG deposition conditions were optimized to have stoichiometry and saturation magnetization close to the bulk, and the presented depositions were at an rf power of 180 watt in a mixed gas of Ar=3.8 SCCM and O2=1.2 SCCM. The rate of deposition is 2.17 nm/min. As-deposited YIG films were annealed at various temperatures (700-900 oC) in air for 3hours and subsequently the structural and compositional characterization was performed by XRD and XRF respectively. It was found that 900 oC annealed samples have a compositional stoichiometry close to bulk value. The surface morphology of these films was studied by atomic force microscopy (AFM). Figure 1 shows the AFM image ofa 100-nm thick YIG without and with a Pt buffer layer annealed at the temperature of 900 oC. The grain size of the YIG film with the buffer layer is much larger than that of the YIG film without the buffer layer, and the average values are several hundred nanometers. Surface roughness of YIG films without and with the buffer layer are 4.50 nm and 2.47 nm, respectively. This result means that the Pt buffer layer improves the grain size and surface roughness of the post annealed YIG film. Static magnetic properties of films were measured by vibrating sample magnetometer (VSM). Magnetization dynamics of films were estimated by the ferromagnetic resonance (FMR) spectra using the coplanar waveguide (CPW) and the vector network analyzer (VNA). These measurements were performed at room temperature. Saturation magnetization (Ms) keeps constant regardless of thickness and the buffer layer. As for their values, the samples with the buffer layer had higher magnetization than the samples without the buffer layer, and are much close to the bulk value (143 emu/cc), which might be correlated with the improvement of surface morphology by the buffer layer. Figure 2 shows the thickness dependence of Gilbert damping parameter (α) in YIG films without and with the Pt buffer layer. In every case, α increases as the film thickness decreases. Their values of the films with the buffer layer become lower than that of films without the buffer layer, and are very close to the bulk value . For example 100-nm thick YIG film has α~3.5×10-4 and 11.4×10-4 for the Pt-buffered and non-buffered cases, respectively. This result may be extrinsic in origin, as Pt-buffered films have both larger grain size and lower roughness, thus lower α, however due to the high structural in-homogeneity in the films without the buffer layer have higher α. On the basis of these results, it is revealed that the damping parameter can be significantly reduced by improving the surface morphology by using a Pt buffer layer which may act as a lower electrode in magnonics and spintronics applications. This work was partly supported by the SCOPE program (Contract No. 0159-0058) from Ministry of Internal Affairs and Communications, Japan. This work was supported in part by JSPS KAKENHIGrant NumberJP26289082 from MEXT, Japan. This work was also supported in part by the Murata Science Foundation and ASRC in Japan.
© 2017 IEEE.
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2017/8/10
Y1 - 2017/8/10
N2 - Recently, yttrium iron garnet (YIG, Y3Fe5O12) has been proved to be an efficient material for magnonics and spintronics application after discovery of spin pumping , spin seebeck effect  and spin hall magnetoresistance  phenomena.
AB - Recently, yttrium iron garnet (YIG, Y3Fe5O12) has been proved to be an efficient material for magnonics and spintronics application after discovery of spin pumping , spin seebeck effect  and spin hall magnetoresistance  phenomena.
UR - http://www.scopus.com/inward/record.url?scp=85034624805&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85034624805&partnerID=8YFLogxK
U2 - 10.1109/INTMAG.2017.8007657
DO - 10.1109/INTMAG.2017.8007657
M3 - Conference contribution
AN - SCOPUS:85034624805
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