Polycrystalline Bi substituted YIG ferrite processed via low temperature sintering

Accepted Manuscript Polycrystalline Bi substituted YIG ferrite processed via low temperature sintering Ning Jia, Zhang Huaiwu, Jie Li, Yulong Liao, Lichuan Jin, Cheng Liu, Vincent G. Harris PII:

S0925-8388(16)33335-7

DOI:

10.1016/j.jallcom.2016.10.201

Reference:

JALCOM 39368

To appear in:

Journal of Alloys and Compounds

Received Date: 15 August 2016 Revised Date:

18 October 2016

Accepted Date: 21 October 2016

Please cite this article as: N. Jia, Z. Huaiwu, J. Li, Y. Liao, L. Jin, C. Liu, V.G. Harris, Polycrystalline Bi substituted YIG ferrite processed via low temperature sintering, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.10.201. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Polycrystalline Bi substituted YIG Ferrite processed via Low Temperature Sintering Jia, Ning1; Zhang, Huaiwu1; Li, Jie1; Liao, Yulong1; Jin, Lichuan1; Liu, Cheng1 and

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Harris, Vincent G. 2

1. University of Electronic Science and Technology of China, Chengdu, Sichuan, China.

2. Department of Electrical and Computer Engineering, Center for Microwave

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Magnetic Materials and Integrated Circuits (CM3IC), Northeastern University,

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Boston, MA USA 02115

Abstract - Polycrystalline Bi substituted YIG ferrite (i.e., Y3-xBixFe5O12) has been widely studied due to its high electrical resistivity, moderate to high magnetization and permeability, and relatively low processing cost. Furthermore, it is suitable for large-scale industrial production making it a viable material for mass-produced filters, inductors, isolators, and other rf components. However, low temperature co-fired

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ceramic technology requires sintering temperatures below ~960 °C (i.e., the approximate melting point of the silver electrodes are ~961 oC) while maintaining a low ferromagnetic resonance linewidth (∆H) and other desirable properties. This work reports the effect of bismuth addition on the ferromagnetic properties of

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low-temperature sintered Y3-xBixFe5O12 (x=0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2) garnet ferrites are reported. The microstructure, magnetic properties, and gyromagnetic properties of the Bi-YIG samples were characterized by X-ray diffraction, scanning microscopy (SEM),

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electron

vibrating

sample

magnetometer

(VSM),

and

ferromagnetic resonance (FMR). Results support the processing of pure phase garnet, with moderate values of saturation magnetization and FMR linewidth for x = 0.9. Moreover, the Fano algorithm was shown to provide superior fitting to asymmetric FMR spectra allowing for very accurate measurement of ∆H. KEYWORDS: LTCC, Bi-YIG, FMR linewidth, Fano fitting.

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ACCEPTED MANUSCRIPT I. Introduction Yttrium iron garnet (i.e., Y3Fe5O12), known as YIG, has been widely studied due to its excellent gyromagnetic performance and singular application potential due to its extraordinary low ferromagnetic resonance linewidth values. YIG finds unique device

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utility in microwave communication devices such as circulators, gyrators and phase shifters due to its low ferromagnetic resonance linewidth, high electrical resistivity and low dielectric loss compared to all other ferrite materials over the lower end of the RF and microwave spectrum [1].

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YIG exists in the garnet crystal structure that is cubic and belongs to the space group Ia3d [2]. It has three different crystallographic cation sites: 16 Fe3+ cations

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occupy in octahedral [a] sites, 24 Fe3+ cations occupy the tetrahedral (d) sites and 24 Y3+ cations in the dodecahedral {c} sites. Meanwhile all of the cation sites are occupied with no vacancies. This characteristic is the reason that YIG has excellent rf magnetic properties as well as chemical and thermal stability. The net magnetic moment arises from the antiparallel alignment of the Y3+ magnetic moments on the {c}

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sites with respect to the anti-ferromagnetically coupled magnetic moments on the [a] and (d) sites [3]. The cation distribution on the [a] and (d) sites play an important role in determining its rf magnetic properties.

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Over the past two decades, LTCC (i.e., low temperature co-fired ceramics) technology has experienced remarkable advances. The combination of YIG and LTCC may result in a great opportunity for both further study of YIG’s fundamental

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properties as well as its industrial and market potential. However, the ideal sintering temperature of YIG is about 1450 °C, which is much higher than temperatures required for LTCC, which are typically lower than the melting point of Ag at ~961oC. A series of experiments have been performed in which the permittivity and permeability characteristics of low temperature processed YIG-based samples have been reported [4-10], [11, 12]. Specifically, the effect of trivalent In substitution on lowering the effective sintering temperature of YIG to ~1050oC were studied by Xu et al. [4], Guo et al., [6], and Niyaifar et al [10]. Huang et al., found that the addition of tetravalent Zr in (Ca,V)-YIG increased the lattice constant and lowered the effective 2

ACCEPTED MANUSCRIPT sintering temperature [5]. A study of divalent Cu addition was found effective in reducing the sintering temperature from about 1450 °C to ~1050 °C [7], revealing the possibility of reducing the sintering temperature by the addition of heavy cations. Unique phenomena have been demonstrated, for example, the addition of C has led to

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an insulator to conductor transition [11] and the addition of Ag particles resulted in the simultaneous negative permeability and permittivity [12]. Lee et al. [8] and Hong et al. [9] succeeded in sintering YIG at ~900°C by introduction of trivalent Bi cations. These last studies were key motivators for the present study in which Bi-oxide was

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used as a fluxing agent while concomitantly employing Bi as a substitutional cation.

Here, we report the achievement of lowering the sintering temperature of YIG

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below that of the melting temperature of Ag commonly used as an electrode material in LTCC processing of passive rf components. This was accomplished by the addition of Bi2O3 fluxing agent in the sintering of Y3-xBixFe5O12 (x=0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2) garnets. Sample microstructure, magnetic properties, and gyromagnetic properties were characterized by X-ray Diffraction, Scanning Electron Microscopy

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(SEM), Differential Scanning Calorimetry (DSC), Vibrating Sample Magnetometer (VSM), and Ferromagnetic Resonance (FMR). Additionally, the relationship between the lattice constant and density with Bi content, sintering temperature, average

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particle size, and saturation magnetization were illuminated. It was found that the FMR linewidth varied logarithmically with Bi content reaching a minimum for the x=0.9 sample. The FMR spectra were also found

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asymmetric compared to the anticipated symmetric Lorentzian line shapes. For many years, the Lorentzian formula was regarded as the intrinsic lineshape of FMR. This spectral feature is frequently modified by the presence of several independent resonances of different physical origins, where the lineshape is simply the sum of the intensities of contributing individual resonances. In other words, interference effects owing to interacting resonances are experienced in many material systems. Here, we explore different lineshape fitting algorithms including the Fano fitting model.

II. Experimental 3

ACCEPTED MANUSCRIPT I.A Sample preparation The raw materials used to process Bi-YIG were Y2O3 (99.9% purity), Fe2O3 (99.5% purity) and Bi2O3 (99% purity). These constituents were weighed with an accuracy of 0.01 g at nominal values coinciding with the stoichiometry of Y3-xBixFe5O12 (x = 0.5,

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0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2). The mixtures were wet milled in a planetary ball mill for 12 h in distilled water with steel balls. The slurry was dried and pre-sintered at 880 °C for 2 h. The pre-sintered powders were again milled for 12 h. After 36 h of drying, the powders were pelleted with PVA (polyvinyl alcohol), screened and

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pressed into toroids using 10 MPa of pressure. Finally, the samples were sintered at 950 °C for 3 h in air with a heating rate of 2 °C/min and then furnace cooled to room

II.B Sample characterization

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temperature.

The crystalline structure of the sintered samples was determined by θ -2θ powder diffraction at room temperature over a range of 2θ = 20° to 80°. The densities were measured using the Archimedes’ method. The microstructure of the samples was

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measured by scanning electron microscope (SEM; JEOL JSM-6490). While the magnetic properties, in the form of M vs. H hysteresis loops, were measured at room temperature using a BHV-525 vibrating sample magnetometer (VSM). FMR

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measurements were carried out at X band using a microwave cavity in a TE102 mode, where the external magnetic field was aligned in the vertical direction relative the

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sample plane.

III. Results and discussion III.A Structural analysis Figure 1 shows the XRD patterns of the Bi-YIG samples with different amounts

of Bi2O3. It is seen from the XRD spectra that the samples exhibit the garnet phase with small spurious peaks evidence of the presence of small volumes of impurity phases, whose amounts were too low to be detected by XRD. However, the principle garnet phase becomes pure at x = 0.9. At the same time, when x = 0.9, XRD patterns conform in peak intensity and placement to the standard PDF form #43-0507. The 4

ACCEPTED MANUSCRIPT lattice constants are shown in the figure 1 (c). Values increase linearly with increasing Bi. This is attributed to the fact that trivalent Bi ions were incorporated into the lattice with no bismuth oxide phase remaining. Figure 2 illustrates differential scanning calorimetry (DSC) curves of Bi-YIG

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samples for x = 0.5 – 2.0. According to DSC analyses, the curves present a measurable increase in amplitude at about 550-650 °C. It is over this temperature range that an evolution in phase occurs. From this we conclude that the addition of Bi effectively decreases the sintering temperature as is shown in the inset curves (b) and

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(c).

Figure 3 shows the cross-section SEM images of Bi-YIG ferrites with x = 0.5 –

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1.2. It can be seen that not all the sintered samples consist of fine grains. From Figs. 3 (a) and (b), the grains remain largely spheroidal and experience limited coarsening. The degree of porosity limits their magnetic utility. Starting from sample (d), grains begin to coarsen, forming more and more identifiable grain boundaries. This result reveals that Bi3+ substitution in Bi-YIG ferrites influences grain refinement and

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sintering enhancement. This is in agreement with the reports of others [3, 8, 11]. Therefore, it is believed that the microstructural features of the Bi-YIG ferrites not only are closely related to chemical composition but also depend upon mean particle

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size of the initial powders, the density of the green body, and the sintering conditions. What’s more, the average particle size of samples having different x content are measured and shown in Fig. 3 (i). It is obvious that for x~0.9, a sharp increase occurs

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which translates to a positive enhancement in the magnetic properties and a reduction in linewith ∆H.

III.B DC Magnetic properties

Figure 4 shows the magnetic hysteresis loops (M vs. H curves) for Bi-YIG with x

= 0.5 to 1.2. The curves reveal excellent soft d.c. magnetic properties as evidenced by low magnetic remanence (Mr) and low coercive field values. Figures 5 and 6 show the values of saturation magnetization Ms and coercivity. It is seen that the saturation magnetization and coercivity change dramatically in response to increasing x. For the sintering temperature of 950 °C, the saturation magnetization remains at a high value 5

ACCEPTED MANUSCRIPT of between 14.5 emu/g to 15.25 emu/g. This trend decreases sharply for x > 0.9. The coercivity improves slightly with the amount of Bi addition. The coercivity remained stable when x > 0.9 at about 41 Oe. These results show that upon the substitution of trivalent Bi cations an obvious positive impact occurs upon the soft magnetic

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properties of Bi-YIG ferrites sintered at temperatures as low as 950 °C. In summary, the sample with x = 0.9 possesses the best soft magnetic properties. Fig. 7 shows the linear relationship between coercivity and density revealing the important role of porosity.

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III.C Gyromagnetic properties

Figure 8 displays the variation in FMR Linewidth ∆H and the density of Bi-YIG

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samples sintered at 950 °C as a function of Bi content (x). Primarily, the density increases with the addition of Bi3+. This is to be expected since the atomic weight of Bi, i.e., 208.98 g/mole, is much higher than that of Y. Replacing Bi3+ with Y3+ is expected to increase the theoretical density. However, the largest effect of the Bi2O3 as a fluxing agent in low temperature sintering is in the formation of a liquid phase

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forming between grains during sintering thus enhancing grain boundary diffusion and Ostwald ripening of grains [13]. An important observation is the apparent logarithmic dependency of ∆H with respect to the increased concentration of the fluxing agent.

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We believe this is the first such observation of such an affect. Figure 9 (a) shows the power absorption spectrum near FMR for the x = 0.9 specimen sintered at 950 °C. Traditionally, the fundamental line shape is that of a

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Lorentzian curve [14-16] and can be expressed as:

F ( x) ∝

A B + x2 2

(1)

However, the measured data displays a degree of asymmetry in the “tails” of the

peak and in this region the Lorentzian curve fitting of equation (1) is relatively poor. In 1969, Fano proposed a new type of resonance that now bares his name, see equation (2). In contrast to the Lorentzian resonance line shape, the Fano resonance exhibits a distinct asymmetry in the “tails” region of the peak. This line shape can be fitted using the following expression[17]: 6

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( F γ + ω − ω0 ) 2 (ω − ω0 ) 2 + γ

(2)

where ω0 and γ are standard parameters that denote the position and width of the resonance, respectively; F is the so-called Fano parameter, which describes the degree

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of asymmetry. From the fitting of the spectrum of Fig. 9 (a), it is seen that the Fano fitting is superior in fitting the overall line shape including the “tails” region. This is best seen in Fig. 9 (b).

Table 1 and Fig. 9 (b) show the improvement of the Fano fit to the classic

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Lorentz fit. The Fano fit SSE is over 50 % smaller to the Lorentz fit meanwhile the Adjustable R-Square is closer to 1, which means the Fano fitting is superior. Besides,

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the residual of the Lorentz fit undulates between ± 0.3 compared with the Fano fit undulating between ± 0.15. The dimensionless parameter q describes the ratio between resonant and nonresonant transition amplitudes in the scattering process[18]. The results prove that the Fano fit performs superior to than of the Lorentz fit.

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IV. Summary and Conclusion

Here, we report the achievement of lowering the sintering temperature of Bi-YIG below that of the melting temperature of Ag, commonly used as an electrode material

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in LTCC processing of passive rf components. This was accomplished by the addition of the Bi2O3 fluxing agent in the sintering of Y3-xBixFe5O12 (x=0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2) garnets. The microstructure, magnetic properties, and gyromagnetic

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properties of the Bi-YIG samples were characterized by X-ray diffraction, scanning electron

microscopy (SEM),

vibrating

sample

magnetometer

(VSM),

and

ferromagnetic resonance (FMR), respectively. The principle findings include: (1) Results support the growth of a pure phase garnet, with high densities (~5.75 g/cc), moderate values of saturation magnetization (Ms) 15.25 emu/g and FMR linewidths (~254.5 Oe at X-band) for the x=0.9 samples. (2) The coercive fields were of the order of 40 Oe and tracked closely with the samples’ density. 7

ACCEPTED MANUSCRIPT (3) The trend in FMR linewidth saw the reduction from x=0 to x=0.9 as >1800 Oe to ~254.5 Oe, respectively. The decline in ∆H with increasing x follows a logarithmic dependency. (4) The Fano algorithm was found best suited in fitting of the FMR curve’s

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asymmetry and allowed for very accurate measurements of ∆H. These findings indicate that Bi2O3 is an effective fluxing agent in reducing the sintering temperature to below the melting point of Ag, and although the FMR linewidths were of moderate values, ~254.5 Oe, these values remain suitable for the

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processing of high performance rf passive components using the LTCC method.

These results show great promise for the application of LTCC to YIG-based

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products allowing for industrial scale processing of this valuable rf material.

Acknowledgement

This work was partly supported by the National High-tech R&D Program of China (863 Program, Grant No. 2015AA034102), the National Natural Science

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Foundation of China (Nos. 51132003, 51402041 and 61571079), the National Basic Research Program of China (Grant No. 2012CB933104), the International Cooperation Project (No. 2012DFR10730), the 111 Talent Recruitment Project (No.

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B1302).

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References [1] V.G. Harris, Modern Microwave Ferrites, IEEE Trans. Magn., 48 (2012) 1075-1104. [2] V.G. Harris, A. Geiler, Y.J. Chen, S.D. Yoon, M.Z. Wu, A. Yang, Z.H. Chen, P. He, P.V. Parimi, X. Zuo, C.E. Patton, M. Abe, O. Acher, C. Vittoria, Recent advances in processing and applications of microwave ferrites, J. Magn. Magn. Mater., 321 (2009) 2035-2047. [3] J.Q. Wang, J. Yang, Y.L. Jin, T. Qiu, Effect of manganese addition on the microstructure and electromagnetic properties of YIG, J. Rare Earths, 29 (2011) 562-566. [4] Q.M. Xu, W.B. Liu, L.J. Hao, C.J. Gao, X.G. Lu, Y.A. Wang, J.S. Zhou, Effects of In-substitution on the microstructure and magnetic properties of Bi-CVG ferrite with low temperature sintering, J. Magn. Magn. Mater., 322 (2010) 2276-2280. [5] Y.Y. Huang, J. Yang, T. Qiu, J.Q. Wang, Y.L. Jin, Effects of Zr-substitution on microstructure and properties of YCaVIG ferrites, J. Magn. Magn. Mater., 324 (2012) 934-938. [6] C.J. Guo, W. Zhang, R.J. Ji, Y.W. Zeng, Effects of In3+-substitution on the structure and magnetic properties of multi-doped YIG ferrites with low saturation magnetizations, J. Magn. Magn. Mater., 323 (2011) 611-615. [7] J.P. Ganne, R. Lebourgeois, M. Pate, D. Dubreuil, L. Pinier, H. Pascard, The electromagnetic properties of Cu-substituted garnets with low sintering temperature, J. Eur. Ceram. Soc., 27 (2007) 2771-2777. [8] H. Lee, Y. Yoon, H. Yoo, S.A. Choi, K. Kim, Y. Choi, H. Melikyan, T. Ishibashi, B. Friedman, K. Lee, Magnetic and FTIR studies of BixY3-xFe5O12 (x=0, 1, 2) powders prepared by the metal organic decomposition method, J. Alloy. Compd., 509 (2011) 9434-9440. [9] R.Y. Hong, Y.J. Wu, B. Feng, G.Q. Di, H.Z. Li, B. Xu, Y. Zheng, D.G. Wei, Microwave-assisted synthesis and characterization of Bi-substituted yttrium garnet nanoparticles, J. Magn. Magn. Mater., 321 (2009) 1106-1110. [10] M. Niyaifar, A. Beitollahi, N. Shiri, M. Mozaffari, J. Amighian, Effect of indium addition on the structure and magnetic properties of YIG, J. Magn. Magn. Mater., 322 (2010) 777-779. [11] M. Chen, X. Wang, Z.D. Zhang, K. Sun, C.B. Cheng, F. Dang, Negative permittivity behavior and magnetic properties of C/YIG composites at radio frequency, Mater. Des., 97 (2016) 454-458. [12] Z.C. Shi, R.H. Fan, Z.D. Zhang, K.L. Yan, X.H. Zhang, K. Sun, X.F. Liu, C.G. Wang, Experimental realization of simultaneous negative permittivity and permeability in Ag/Y3Fe5O12 random composites, J. Mater. Chem. C, 1 (2013) 1633-1637. [13] T.C. Zhou, H.W. Zhang, L.J. Jia, Y.L. Liao, Z.Y. Zhong, F.M. Bai, H. Su, J. Li, L.C. Jin, C. Liu, Enhanced ferromagnetic properties of low

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temperature sintering LiZnTi ferrites with Li2O-B2O3-SiO2-CaO-Al2O3 glass addition, J. Alloy. Compd., 620 (2015) 421-426. [14] J.F. Sierra, F.G. Aliev, R. Heindl, S.E. Russek, W.H. Rippard, Broadband ferromagnetic resonance linewidth measurement of magnetic tunnel junction multilayers, Appl. Phys. Lett., 94 (2009). [15] N.G. Chechenin, C.B. Craus, A.R. Chezan, T. Vystavel, D.O. Boerma, J.T.M. De Hosson, L. Niesen, Relation between observed micromagnetic ripple and FMR width in ultrasoft magnetic films, IEEE Trans. Magn., 38 (2002) 3027-3029. [16] Z. Zhang, L. Bai, X. Chen, H. Guo, X.L. Fan, D.S. Xue, D. Houssameddine, C.M. Hu, Observation of thermal spin-transfer torque via ferromagnetic resonance in magnetic tunnel junctions, Physical Review B, 94 (2016). [17] I.S. Maksymov, A.E. Miroshnichenko, Active control over nanofocusing with nanorod plasmonic antennas, Opt. Express, 19 (2011) 5888-5894. [18] M. Galli, S.L. Portalupi, M. Belotti, L.C. Andreani, L. O'Faolain, T.F. Krauss, Light scattering and Fano resonances in high-Q photonic crystal nanocavities, Appl. Phys. Lett., 94 (2009) 3.

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ACCEPTED MANUSCRIPT Table. 1. Fitting results of the power absorption spectrum using Lorentzian and Fano functions. Function

y = y0 +

w π 4( x − xc ) 2 + w2

Y = A+ F

[ q + 2( H − H 0 ) / ∆H ]2 1 + [2( H − H 0 ) / ∆H ]2

Lorentz

Fano

∆H (Oe)

258.3

254.5

SSE

4.81

2.09

Adj. R-Square

0.992

0.997

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Fitting Curve

2A

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SSE: Sum of Squares for Error;

Adj. R-Square: a modified version of R-squared that has been adjusted for the number of adjustable

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parameters in the model.

x=1.0

x=0.9

PDF#43-0507

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(6 4 2) (5 5 2) (6 4 0) (6 4 4) (6 3 1)

(5 3 2)

(4 3 1)

(4 4 0) (5 2 1)

(4 2 2) (3 3 2)

(4 2 0)

(3 2 1)

(4 0 0)

(2 2 0) (2 1 1)

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x=1.2 (6 6 4) (8 4 2) (8 4 0)

x=1.1

Intensity (a.u.)

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x=0.7

x=0.6

x=0.5

Intensity (a.u.)

(6 6 4) (8 4 2) (8 4 0)

(8 0 0) (6 5 1) (6 4 2) (5 5 2) (6 4 0) (6 4 4) (6 3 1) (5 3 2) (4 4 0) (5 2 1) (4 3 1) (4 2 2) (3 3 2)

(4 2 0) (4 0 0) (3 2 1)

(2 1 1)

80 70 30 40 50 60 2-Theta (degree) 20

10

x=0.8 (2 2 0)

1(a)

80

70

30 40 50 60 2-Theta (degree) 20 10

1(b)

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PDF#43-0507

ACCEPTED MANUSCRIPT 12.47

12.45 12.44 12.43 12.42 12.41

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Lattice Contants

12.46

Lattice Contant 12.40 0.6

0.7

0.8

0.9

Content (x)

1.0

1.1

1.2

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0.5

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Fig. 1(a) and (b) XRD patterns of Bi-YIG ferrites sintered at 950 °C: x = 0.5, 0.6, 0.7,

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0.8, 0.9, 1.0, 1.1, 1.2. 1 (c) The lattice constant varies as x increases from 0.5 to 1.2.

ACCEPTED MANUSCRIPT Temperature (degree) 550

600

(b)

700 0.5

1.0

1.5

600

 




 550




0.6

650

Tx (degree)






0.8

2.0

(c)




1.0

500

0.4

x = 0.5 x= 1 x = 1.5 x= 2

7 5

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Value (mW/g)

650

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500 1.2

Content (x)

1

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3

(a)

0

200

400

600

800

1000

Temperature (degree)

Fig. 2. (a) The DSC curves of Bi-YIG for x = 0.5, 1, 1.5 2. The DSC curves for the

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Bi-YIG powder. (b) An expanded view of the temperature range in which a structural evolution occurs. (c) The identified temperatures obtained from the peaks of the DSC curves shown in (b) confirming the reduction in sintering temperature with increasing

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Bi2O3.

2.4 2.2

B

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Average Particle Size (µm)

2.6

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2.0 1.8

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1.6 1.4 1.2

(i)

1.0

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Content (x) Fig. 3. SEM micrographs of Bi-YIG ferrites, sintered at 950 °C: (a) x = 0.5; (b) x = 0.6; (c) x = 0.7; (d) x = 0.8; (e) x = 0.9; (f) x = 1.0; (g) x = 1.1; (h) x = 1.2. (i) The average particle size

20 15 10 5 x=0.5 x=0.6 x=0.7 x=0.8 x=0.9 x=1.0 x=1.1 x=1.2

-5 -10 -15 -20 -3000 -2000 -1000

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0

0 1000 2000 3000 H (Oe)

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Saturation Magnetization (emu/g)

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Fig. 4. Hysteresis loop of Bi-YIG ferrites, sintered at 950 °C, x = 0.5

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–

1.2.

16 15

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14 13 12

0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Content (x)

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Saturation Magnetization (emu/g)

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Fig. 5. Saturation Magnetization (Ms) of Bi-YIG ferrites, sintered at 950°C, x = 0.5 –

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1.2.

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41 40 39

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Coercivity Field (Oe)

42

38 37 36

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0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Content (x)

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Fig. 6. Coercivity of Bi-YIG ferrites, sintered at 950°C, x = 0.5 – 1.2.

ACCEPTED MANUSCRIPT 42

40

38 37 36 5.3

5.4

5.5 5.6 5.7 5.8 3 Density (g/cm )

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39

5.9

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Fig. 7. Coercivity vs. density.

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6.0

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Coecivity Field (Oe)

41

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1

6.0 5.9 5.8 5.7 5.6 5.5 5.4 5.3 5.2 5.1 5.0

3

1.5

0.0

0.2

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0.5

0.4 0.6 0.8 Bi content (x)

1.0

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FMR Linewidth ∆H (kOe)

2

Density (g/m )

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1.2

Fig. 8. The linewidth ∆H and the density of Bi-YIG sintered at 950 °C with the

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increasing of Bi’s substitution.

-26 -27 -28

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-29 -30 -31 -32 2000

test data Fano fitting curve Lorentz fitting curve

2500 3000 3500 4000 4500 Megnetic Field Intensity (Oe)

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Resonance Absorption (dB)

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1.0

Fano Fit Curve Lorentz Fit Curve

0.5 0.0 -0.5 -1.0

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Regular Residual

(a)

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Megnetic Field (Oe)

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Fig. 9(a). The Fano fitting and Lorentz fitting curves of the resonance absorption, 0.9 doped of Bi and sintering at 950 °C. (b). The Regular Residual of fitting data. The

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black is Fano fit and the red is Lorentz fit.

ACCEPTED MANUSCRIPT Dear Editor, There are several highlights in my manuscript entitled “Polycrystalline Bi-YIG Ferrite processed via Low Temperature Sintering” publication in the Journal of Alloys and Compounds. A new method – Bi’s adoption was found to decrease the sintering temperature. And an advanced measurement of FMR was applied. It showed a regular curve related to the average particle size. We applied the Fano fitting to have best values representing the experiment results.

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1. 2. 3. 4.

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Thank you.

Sincerely, Jia Ning and Zhang Huaiwu

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Disclosure: The authors declare that V. G. Harris is an Editor for Journal of Alloys and Compounds.

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University of Electronic Science and Technology of China Chengdu, Sichuan, China.