- Email: [email protected]
Y3Fe5O12 composites
Journal of Alloys and Compounds 641 (2015) 223–227
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Preparation and characterization of BaFe12O19/Y3Fe5O12 composites Ying Lin a,b,⇑, Pan Kang a, Haibo Yang a, Miao Liu a a b
School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China Shaanxi Research Institute of Agricultural Products Processing Technology, Xi’an 710021, China
a r t i c l e
i n f o
Article history: Received 22 January 2015 Received in revised form 20 March 2015 Accepted 23 March 2015 Available online 20 April 2015 Keywords: Composites Magnetic materials Sol–gel chemistry Magnetic properties
a b s t r a c t BaFe12O19/Y3Fe5O12 (BaM/YIG) composites with giant enhancement of magnetic energy product ((BH)max) were fabricated by microwave sintering the BaM/YIG composite powders, which were firstly prepared using a simple sol–gel method. The phase composition and surface morphology of the as-synthesized composites were characterized by an X-ray diffractometer and a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, respectively. The magnetic properties of the composites were investigated by a vibrating sample magnetometer. All the composites show single-phaselike magnetic hysteresis loops. The results reveal the hard phase (BaM) and soft phase (YIG) are well exchange coupled and the introduction of YIG could significantly enhance the remnant magnetization (Mr), coercivity (Hc) and (BH)max of BaM. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the composite spring exchange magnets have attracted considerable attentions due to the prediction for getting higher magnetic energy product (BH)max [1]. Early in the 1990s, the concept of the exchange spring coupling behavior in composite magnets was proposed first. According to the exchange spring concept, exchange coupled composite permanent magnets can have magnetic properties by combining the high magnetic anisotropy of the hard phase and the high saturation magnetization of the soft phase, which are superior to those of single-phase magnets and exhibit high (BH)max [1–3]. Previous studies of permanent magnets with high (BH)max mainly focus on alloy composites [4–7]. The alloy composites have a very high (BH)max but the cost of preparation is high and the corrosion resistance is poor. In contrast, the hard ferrites can overcome these shortcomings. It has low cost, excellent chemical stability, and corrosion resistance, but the (BH)max is low, which seriously hinders the applications. Hence, improving the (BH)max of hard ferrites is inevitable. Exchange spring mechanism would be a good solution for improving the (BH)max of hard ferrites. Recently, composite ferrites have been attracting an increasing interest. They can be widely used in magnetic recording media, magnetic fluids, microwave devices, permanent magnets and biomedicines [8–10]. As a typical
⇑ Corresponding author at: School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China. Tel./fax: +86 29 86168688. E-mail addresses: [email protected] (Y. Lin), [email protected] (H. Yang). http://dx.doi.org/10.1016/j.jallcom.2015.03.265 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
hard ferrite, barium ferrite (BaFe12O19) is a high performance permanent magnet. It has been extensively investigated because of its fairly large magnetocrystalline anisotropy, high Curie temperature, relatively large magnetization, high electrical resistance, low cost, excellent chemical stability, and excellent corrosion resistance [11–13], and has a wide application in magnetic recording as well as in microwave devices [14,15]. YIG is one of the most important ferrimagnetic materials, it has controllable saturation magnetization, low dielectric loss tangent and narrow ferromagnetic resonance linewidth in microwave region [16,17]. According to exchange spring mechanism, compositing hard ferrite BaM with soft ferrite YIG could significantly improve the Hc, Mr and (BH)max of BaM. Whereas, the enhanced magnetic properties of the composite magnets are difficult to obtain due to the fact that the Hc and Mr highly depend on the structures, morphologies, particle size and distribution of the soft and hard phases [18,19]. The microwave sintering method has significant advantages over the conventional sintering method. For the microwave sintering method the microwave electromagnetic energy is transferred straight to the material through molecular interactions between the material and the electromagnetic field, thus effectively promote the forward diffusion of ions so as to accelerate the sintering process, decrease densification temperature, inhibit the grain growth and suppress potential chemical reaction between constituents [20–23]. Therefore, microwave sintering method is a better alternative compared with conventional sintering method. In this work, well exchange coupling BaM/YIG hard–soft ferrite composites were fabricated by microwave sintering the green body made from the BaM/YIG composite powders which were prepared
224
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
by calcining the precursor using a simple sol–gel method firstly. It is worth noting that the (BH)max of the BaM can be significantly enhanced by the induction of YIG. As expect, the giant enhancement of (BH)max makes it have an attractive application in permanent magnets, magnetic recording media, magnetic fluids, microwave devices and biomedicines. 2. Experimental procedure The chemical regents used in the work were barium nitrate (Ba(NO3)2), ferric nitrate (Fe(NO3)39H2O), yttrium nitrate (Y(NO3)36H2O), citric acid (C6H8O7H2O) and aqueous ammonia (NH3H2O). All the chemicals were analytical grade purity and were used without further purification. (1 x)BaM/xYIG composite powders (with mass ratio x = 0.1, 0.2, 0.3, 0.4) were prepared through sol–gel process. The preparation process includes the following steps. An aqueous solution of C6H8O7H2O was prepared in distilled water. Then stoichiometric amount of Ba(NO3)2, Fe(NO3)39H2O and Y(NO3)26H2O were added into
Fig. 1. XRD patterns of the BaM/YIG composites with different concentrations of YIG sintered by microwave sintering method at 1150 °C for 10 min.
the solution and magnetically stirred at 80 °C. NH3H2O was added to the above solution to adjust the pH value to 7. After 2 h magnetically stirred the solution was dried at 200 °C for 2 h to form a black color precursor powder. The precursor powders were calcined at 1100 °C for 4 h at air atmosphere to obtain the BaM/ YIG composite powders. Then the obtained BaM/YIG composite powders were pressed into disks after adding some 5 wt% PVA aqueous solution. Final sintering was carried out at 1150 °C for 10 min and the total cycle time was 2.5 h using microwave sintering method. The microwave furnace in this work consists of 2.45 GHz magnetrons with maximum power of 3 kW (Raptor, Shanghai PreeKem, China). The phase structure of the as-prepared BaM/YIG composites was detected by an X-ray diffractometer (XRD) with Cu Ka radiation (Rigaku D/MAX-2400, Japan). The morphology of the composites was analyzed using a scanning electron microscope (SEM) (Hitachi S-4800, Japan) equipped with an energy dispersive X-ray spectroscopy (EDS). The magnetic hysteresis loops of the composites were measured by a vibrating sample magnetometer 113 (VSM) (Lake Shore 7410, USA).
3. Results and discussion Fig. 1 displays the XRD patterns of the BaM/YIG composites with different concentrations of YIG sintered by the microwave sintering method at 1150 °C for 10 min. It can be clearly seen that only the expected phases of BaM and YIG can be detected in all the samples from the figure. Moreover, all the XRD patterns can be perfectly indexed to the hexagonal magnetoplumbite structure of BaM phase (JCPDS 27-1029) and the orthorhombic structure of YIG phase (JCPDS 21-1450), respectively. Within the resolution limit of XRD no any other intermediate phase can be detected. The above X-ray diffractograms reveal that no reaction occurred between the BaM phase and YIG phase. It can be concluded that BaM phase and YIG phase can co-exist after being sintered at 1150 °C with a high crystallinity and without any impurity phases. As expected, with increasing the concentration of YIG, the diffraction peaks of YIG strengthened gradually. The SEM micrographs of the natural surfaces of the BaM/YIG composites with different YIG concentrations sintered at 1150 °C for 10 min are shown in Fig. 2. It can be found that the BaM/YIG composites exhibit uniform distribution, and the granular grains with small size are of cubic YIG phase while the plate-like grains with big size are of hexagonal BaM phase due to the sintering temperature of YIG is higher than that of BaM [24,12]. It can be also
Fig. 2. SEM micrographs of the BaM/YIG composites with different YIG concentrations sintered at 1150 °C for 10 min: (a) 0.9BaM/0.1YIG; (b) 0.8BFO/0.2YIG; (c) 0.7BaM/ 0.3YIG; (d) 0.6BaM/0.4YIG.
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
225
Fig. 3. EDS mapping of the representative 0.7BaM/0.3YIG composites sintered by microwave sintering method at 1150 °C for 10 min.
observed that the grain size of the composites decreases gradually and few pores can be found in the composites with increasing the YIG concentration, this phenomenon may be attributed to the difference sintering temperature of the two phases. Fig. 3 shows the EDS mapping analysis result of the representative 0.7BaM/0.3YIG composite sintered by microwave sintering method at 1150 °C for 10 min. It can be easily found that the composite mainly contains Fe, Ba, Y, O four elements and the four different kinds of colors are uniform, indicating that the related elements are distributed uniformly. In conjunction with the XRD analysis and the SEM images, it can be concluded that the composites only consist of BaM and YIG and the two phases exhibit uniform distribution in the composites. The room temperature magnetic hysteresis (M–H) loops of the pure-phase BaM, pure-phase YIG and the BaM/YIG composites with different concentrations of YIG are shown in Fig. 4(a). It can be seen that all the samples show single-phase-like hysteresis
loops, indicating that the hard phase (BaM) and soft phase (YIG) are well exchange coupled to each other in all the samples. However, through careful observation one can notice that the magnetization curve for the 0.9BaM/0.1YIG composite are smoother than those of the other samples indicating that the BaM phase and the YIG phase are better exchange coupled to each other for the 0.9BaM/0.1YIG composite than those of the other composites. However, it is worth noting that both the Hc and Mr are much higher than those of the pure-phase BaM for all the concentrations of BaM/YIG composites. And this phenomenon accounts for the possible enhancement of (BH)max. Table 1 summarizes the magnetic properties of the pure-phase BaM, pure-phase YIG and BaM/YIG composites. It can be seen that the value of Hc and Mr increases initially and then decreases with increasing the concentration of YIG phase. Actually, the magnetic properties of the two-phase composite depend very much on the distribution of the magnetically soft and hard phases and the average grain sizes
226
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
Fig. 4. (a) Magnetic hysteresis(M–H) loops, (b) magnetic hysteresis (B–H) loops and (c) variation of the (BH)max value of the pure-phase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG.
Table 1 Magnetic properties of the pure-phase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG. Samples
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
BaM YIG 0.9BaM/0.1YIG 0.8BaM/0.2YIG 0.7BaM/0.3YIG 0.6BaM/0.4YIG
49.995 25.756 46.876 46.171 43.918 38.797
16.607 – 27.805 26.576 25.005 19.816
1635.4 – 2580.9 2436.1 2197.6 1933.6
of the individual phases. For isotropic two-phase composite, the small grain size improves both Hc and Mr [25]. In addition to this, there are two main interactions, exchange and dipolar interactions that determine the magnetic property of the two-phase composite. For the as-prepared BaM/YIG composites, at the low concentrations of soft YIG phase, the exchange interaction on the YIG magnetic moments excreted by the hard BaM phase is very strong, which results in the increase of Hc and Mr. With increasing the concentration of YIG, the exchange interaction on the YIG magnetic moments would be enervated and dipolar interaction among YIG grains becomes significant. Therefore the reverse domains in the YIG phase with low nucleation field could be nucleated easily, which causes the decrease of Mr and similar phenomenon also has been found in the BaFe12O19/Ni0.8Zn0.2Fe2O4 composite [19].
In order to evaluate the (BH)max of the BaM/YIG composites, Fig. 4(b) shows the magnetic hysteresis (B–H) loops of the purephase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG. The magnetic hysteresis (B–H) loops were transformed from magnetic hysteresis (M–H) loops, according to B = l0H + 4pM [26]. And the (BH)max values were calculated according to the demagnetization parts of the (B–H) loops. Fig. 4(c) presents the calculated magnetic energy products of the purephase BaM and BaM/YIG composites with different concentrations of YIG. It can be clearly seen that the values of (BH)max for all the BaM/YIG composites are much higher compared with that of the pure-phase BaM. The most important observation is that the 0.9BaM/0.1YIG composite exhibits a (BH)max value of 15.662 kJ/ m3. Hence, a giant enhancement of 290% of the (BH)max can be achieved. In order to further investigate the exchange coupling between the BaM phase and YIG phase, the demagnetization curves of hysteresis loops for the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites with different concentrations of YIG are compared in Fig. 5(a). Smooth demagnetization curves reflect exchange coupling phenomenon between different phases, and if exchange coupling does not exist among the phases in a composite system, the demagnetization curve in the hysteresis loop will present independent demagnetization of each phase [27], it can be seen that the 0.9BaM/0.1YIG composite exhibit a very smooth demagnetization curve, indicating that the BaM phase and the YIG phase are
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
227
Fig. 5. (a) Demagnetization curves and (b) dM/dH of demagnetization curves of the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites with different concentrations of YIG.
very well exchange coupled for the 0.9BaM/0.1YIG composite. And with further increasing YIG concentration the demagnetization curve become more and more rough gradually, reflecting that the exchange coupling between the BaM phase and YIG phase decreases with increasing the concentration of YIG. Fig. 5(b) presents the dM/dH of demagnetization curves for the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites. The dM/ dH of demagnetization curve is an indicative of exchange coupling interactions [3]. The appearance of peak at higher field for each curve is an indicator of the degree of exchange coupling between the two phases. The lower intensity of the peak shows the higher degree of exchange coupling. It can be seen that 0.9BaM/0.1YIG composite is not obvious, indicating very well exchange coupling between the BaM phase and YIG phase. With further increasing the concentration of YIG, the intensity of the peak increases, indicating that the exchange coupling of the BaM/YIG composites decrease with increasing the concentration of YIG. 4. Conclusions In conclusion, the BaM/YIG composites with giant enhancement of (BH)max were successfully synthesized by a simple sol–gel method. The XRD, SEM and EDS analysis reveal that the BaM and YIG phases can coexist with density and uniformly distribution. Magnetic property analysis of the BaM/YIG composites indicate that the BaM and YIG of the 0.9BaM/0.1YIG composite are well exchange coupled and the introduction of YIG could significantly enhance the Mr, Hc and (BH)max compared with pure BaM phase. Moreover, a giant 290% enhancement on (BH)max can be achieved compared with pure BaM phase. Additionally, this study indicates that exchange coupled composite with giant enhancement of Hc, Mr and (BH)max can be fabricated by simple chemical reaction and proper sintering process, which will be technologically important in future.
Technology Foundation of Shaanxi Province (Grant Nos. 2013KJXX79 and 2013JQ6004) and the Special Foundation of the Ministry of Shaanxi Province (Grant No. 2013JK0937) and the Scientific Research Starting Foundation of Shaanxi University of Science and Technology (Grant No. BJ13-13). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
Acknowledgements [27]
This work is supported by the National Natural Science Foundation of China (Grant No. 51402178), the Science and
E.F. Kneller, R. Hawing, IEEE Trans. Magn. 27 (1991) 3588–3600. R. Skomski, J.M.D. Coey, Phys. Rev. B 48 (1993) 15812. D. Roy, P.S.A. Kumar, J. Appl. Phys. 106 (2009) 073902. X.J. Jiang, J.E. Shield, J. Magn. Magn. Mater. 333 (2013) 63–68. A.M. Belemuk, S.T. Chui, J. Appl. Phys. 113 (2013) 043913. J. Zhang, Y.K. Takahashi, R. Gopalan, K. Hono, Appl. Phys. Lett. 86 (2005) 122509. Z. Ahmad, S. Tao, T. Ma, G. Zhao, M. Yan, J. Alloys Comp. 509 (2011) 8952–8957. Y. Wang, Y. Huang, Q.F. Wang, J. Magn. Magn. Mater. 324 (2012) 3024–3028. M.A. Radmanesh, S.A.S. Ebrahimi, J. Magn. Magn. Mater. 324 (2012) 3094– 3098. L.Y. Zhang, Z.W. Li, J. Alloys Comp. 469 (2009) 422–426. S. Castro, M.G. Rivas, J.M. Greneche, J. Mira, C. Rodrlguez, J. Magn. Magn. Mater. 152 (1996) 61–69. L.C. Li, K. Chen, H. Liu, G.X. Tong, H.S. Qian, B. Hao, J. Alloys Comp. 557 (2013) 11–17. Z. Mosleh, P. Kameli, M. Ranjbar, H. Salamati, Ceram. Int. 40 (2014) 7279– 7284. K.S. Martirosyan, E. Galstyan, S.M. Hossain, Yi-Ju Wang, D. Litvinov, Mater. Sci. Eng., B 176 (2011) 8–13. V.V. Soman, V. Nanoti, D. Kulkarni, Ceram. Int. 39 (2003) 5513–5523. W. Zhang, C.J. Guo, R.J. Ji, C.X. Fang, Y.W. Zeng, Mater. Chem. Phys. 125 (2011) 646–651. J.W. Lee, J.H. Oh, J. Magn. Magn. Mater. 272 (2004) 2230–2232. S. Hazra, M.K. Patra, S.R. Vadera, N.N. Ghosh, J. Am. Ceram. Soc. 95 (2012) 60– 63. D. Roy, C. Shivakumara, P.S. Anil Kumar, J. Magn. Magn. Mater. 321 (2009) L11–L14. E.O. Hall, Proc. Phys. Soc. B 64 (1951) 747–753. S. Miglani, A.K. Jha, Mater. Res. Bull. 48 (2013) 1553–1559. S. Rhee, D. Agrawal, T. Shrout, M. Thumm, Ferroelectrics 261 (2001) 15–20. V.K. Sankaranarayanan, C. Sreekumar, Curr. Appl. Phys. 3 (2003) 205–208. A. Mergen, A. Qureshi, J. Alloys Comp. 478 (2009) 741–744. R. Fischer, T. Schrefl, H. Kronmüller, J. Fidler, J. Magn. Magn. Mater. 153 (1996) 35–49. X.Q. Liu, S.H. He, J.M. Qiu, J.P. Wang, Appl. Phys. Lett. 98 (2011) 222507– 222509. H. Zaigham, F.A. Khalid, J. Mater. Sci. Technol. 27 (2011) 218–222.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Preparation and characterization of BaFe12O19/Y3Fe5O12 composites Ying Lin a,b,⇑, Pan Kang a, Haibo Yang a, Miao Liu a a b
School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China Shaanxi Research Institute of Agricultural Products Processing Technology, Xi’an 710021, China
a r t i c l e
i n f o
Article history: Received 22 January 2015 Received in revised form 20 March 2015 Accepted 23 March 2015 Available online 20 April 2015 Keywords: Composites Magnetic materials Sol–gel chemistry Magnetic properties
a b s t r a c t BaFe12O19/Y3Fe5O12 (BaM/YIG) composites with giant enhancement of magnetic energy product ((BH)max) were fabricated by microwave sintering the BaM/YIG composite powders, which were firstly prepared using a simple sol–gel method. The phase composition and surface morphology of the as-synthesized composites were characterized by an X-ray diffractometer and a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, respectively. The magnetic properties of the composites were investigated by a vibrating sample magnetometer. All the composites show single-phaselike magnetic hysteresis loops. The results reveal the hard phase (BaM) and soft phase (YIG) are well exchange coupled and the introduction of YIG could significantly enhance the remnant magnetization (Mr), coercivity (Hc) and (BH)max of BaM. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction In recent years, the composite spring exchange magnets have attracted considerable attentions due to the prediction for getting higher magnetic energy product (BH)max [1]. Early in the 1990s, the concept of the exchange spring coupling behavior in composite magnets was proposed first. According to the exchange spring concept, exchange coupled composite permanent magnets can have magnetic properties by combining the high magnetic anisotropy of the hard phase and the high saturation magnetization of the soft phase, which are superior to those of single-phase magnets and exhibit high (BH)max [1–3]. Previous studies of permanent magnets with high (BH)max mainly focus on alloy composites [4–7]. The alloy composites have a very high (BH)max but the cost of preparation is high and the corrosion resistance is poor. In contrast, the hard ferrites can overcome these shortcomings. It has low cost, excellent chemical stability, and corrosion resistance, but the (BH)max is low, which seriously hinders the applications. Hence, improving the (BH)max of hard ferrites is inevitable. Exchange spring mechanism would be a good solution for improving the (BH)max of hard ferrites. Recently, composite ferrites have been attracting an increasing interest. They can be widely used in magnetic recording media, magnetic fluids, microwave devices, permanent magnets and biomedicines [8–10]. As a typical
⇑ Corresponding author at: School of Materials Science and Engineering, Shaanxi University of Science and Technology, Xi’an 710021, China. Tel./fax: +86 29 86168688. E-mail addresses: [email protected] (Y. Lin), [email protected] (H. Yang). http://dx.doi.org/10.1016/j.jallcom.2015.03.265 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
hard ferrite, barium ferrite (BaFe12O19) is a high performance permanent magnet. It has been extensively investigated because of its fairly large magnetocrystalline anisotropy, high Curie temperature, relatively large magnetization, high electrical resistance, low cost, excellent chemical stability, and excellent corrosion resistance [11–13], and has a wide application in magnetic recording as well as in microwave devices [14,15]. YIG is one of the most important ferrimagnetic materials, it has controllable saturation magnetization, low dielectric loss tangent and narrow ferromagnetic resonance linewidth in microwave region [16,17]. According to exchange spring mechanism, compositing hard ferrite BaM with soft ferrite YIG could significantly improve the Hc, Mr and (BH)max of BaM. Whereas, the enhanced magnetic properties of the composite magnets are difficult to obtain due to the fact that the Hc and Mr highly depend on the structures, morphologies, particle size and distribution of the soft and hard phases [18,19]. The microwave sintering method has significant advantages over the conventional sintering method. For the microwave sintering method the microwave electromagnetic energy is transferred straight to the material through molecular interactions between the material and the electromagnetic field, thus effectively promote the forward diffusion of ions so as to accelerate the sintering process, decrease densification temperature, inhibit the grain growth and suppress potential chemical reaction between constituents [20–23]. Therefore, microwave sintering method is a better alternative compared with conventional sintering method. In this work, well exchange coupling BaM/YIG hard–soft ferrite composites were fabricated by microwave sintering the green body made from the BaM/YIG composite powders which were prepared
224
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
by calcining the precursor using a simple sol–gel method firstly. It is worth noting that the (BH)max of the BaM can be significantly enhanced by the induction of YIG. As expect, the giant enhancement of (BH)max makes it have an attractive application in permanent magnets, magnetic recording media, magnetic fluids, microwave devices and biomedicines. 2. Experimental procedure The chemical regents used in the work were barium nitrate (Ba(NO3)2), ferric nitrate (Fe(NO3)39H2O), yttrium nitrate (Y(NO3)36H2O), citric acid (C6H8O7H2O) and aqueous ammonia (NH3H2O). All the chemicals were analytical grade purity and were used without further purification. (1 x)BaM/xYIG composite powders (with mass ratio x = 0.1, 0.2, 0.3, 0.4) were prepared through sol–gel process. The preparation process includes the following steps. An aqueous solution of C6H8O7H2O was prepared in distilled water. Then stoichiometric amount of Ba(NO3)2, Fe(NO3)39H2O and Y(NO3)26H2O were added into
Fig. 1. XRD patterns of the BaM/YIG composites with different concentrations of YIG sintered by microwave sintering method at 1150 °C for 10 min.
the solution and magnetically stirred at 80 °C. NH3H2O was added to the above solution to adjust the pH value to 7. After 2 h magnetically stirred the solution was dried at 200 °C for 2 h to form a black color precursor powder. The precursor powders were calcined at 1100 °C for 4 h at air atmosphere to obtain the BaM/ YIG composite powders. Then the obtained BaM/YIG composite powders were pressed into disks after adding some 5 wt% PVA aqueous solution. Final sintering was carried out at 1150 °C for 10 min and the total cycle time was 2.5 h using microwave sintering method. The microwave furnace in this work consists of 2.45 GHz magnetrons with maximum power of 3 kW (Raptor, Shanghai PreeKem, China). The phase structure of the as-prepared BaM/YIG composites was detected by an X-ray diffractometer (XRD) with Cu Ka radiation (Rigaku D/MAX-2400, Japan). The morphology of the composites was analyzed using a scanning electron microscope (SEM) (Hitachi S-4800, Japan) equipped with an energy dispersive X-ray spectroscopy (EDS). The magnetic hysteresis loops of the composites were measured by a vibrating sample magnetometer 113 (VSM) (Lake Shore 7410, USA).
3. Results and discussion Fig. 1 displays the XRD patterns of the BaM/YIG composites with different concentrations of YIG sintered by the microwave sintering method at 1150 °C for 10 min. It can be clearly seen that only the expected phases of BaM and YIG can be detected in all the samples from the figure. Moreover, all the XRD patterns can be perfectly indexed to the hexagonal magnetoplumbite structure of BaM phase (JCPDS 27-1029) and the orthorhombic structure of YIG phase (JCPDS 21-1450), respectively. Within the resolution limit of XRD no any other intermediate phase can be detected. The above X-ray diffractograms reveal that no reaction occurred between the BaM phase and YIG phase. It can be concluded that BaM phase and YIG phase can co-exist after being sintered at 1150 °C with a high crystallinity and without any impurity phases. As expected, with increasing the concentration of YIG, the diffraction peaks of YIG strengthened gradually. The SEM micrographs of the natural surfaces of the BaM/YIG composites with different YIG concentrations sintered at 1150 °C for 10 min are shown in Fig. 2. It can be found that the BaM/YIG composites exhibit uniform distribution, and the granular grains with small size are of cubic YIG phase while the plate-like grains with big size are of hexagonal BaM phase due to the sintering temperature of YIG is higher than that of BaM [24,12]. It can be also
Fig. 2. SEM micrographs of the BaM/YIG composites with different YIG concentrations sintered at 1150 °C for 10 min: (a) 0.9BaM/0.1YIG; (b) 0.8BFO/0.2YIG; (c) 0.7BaM/ 0.3YIG; (d) 0.6BaM/0.4YIG.
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
225
Fig. 3. EDS mapping of the representative 0.7BaM/0.3YIG composites sintered by microwave sintering method at 1150 °C for 10 min.
observed that the grain size of the composites decreases gradually and few pores can be found in the composites with increasing the YIG concentration, this phenomenon may be attributed to the difference sintering temperature of the two phases. Fig. 3 shows the EDS mapping analysis result of the representative 0.7BaM/0.3YIG composite sintered by microwave sintering method at 1150 °C for 10 min. It can be easily found that the composite mainly contains Fe, Ba, Y, O four elements and the four different kinds of colors are uniform, indicating that the related elements are distributed uniformly. In conjunction with the XRD analysis and the SEM images, it can be concluded that the composites only consist of BaM and YIG and the two phases exhibit uniform distribution in the composites. The room temperature magnetic hysteresis (M–H) loops of the pure-phase BaM, pure-phase YIG and the BaM/YIG composites with different concentrations of YIG are shown in Fig. 4(a). It can be seen that all the samples show single-phase-like hysteresis
loops, indicating that the hard phase (BaM) and soft phase (YIG) are well exchange coupled to each other in all the samples. However, through careful observation one can notice that the magnetization curve for the 0.9BaM/0.1YIG composite are smoother than those of the other samples indicating that the BaM phase and the YIG phase are better exchange coupled to each other for the 0.9BaM/0.1YIG composite than those of the other composites. However, it is worth noting that both the Hc and Mr are much higher than those of the pure-phase BaM for all the concentrations of BaM/YIG composites. And this phenomenon accounts for the possible enhancement of (BH)max. Table 1 summarizes the magnetic properties of the pure-phase BaM, pure-phase YIG and BaM/YIG composites. It can be seen that the value of Hc and Mr increases initially and then decreases with increasing the concentration of YIG phase. Actually, the magnetic properties of the two-phase composite depend very much on the distribution of the magnetically soft and hard phases and the average grain sizes
226
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
Fig. 4. (a) Magnetic hysteresis(M–H) loops, (b) magnetic hysteresis (B–H) loops and (c) variation of the (BH)max value of the pure-phase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG.
Table 1 Magnetic properties of the pure-phase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG. Samples
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
BaM YIG 0.9BaM/0.1YIG 0.8BaM/0.2YIG 0.7BaM/0.3YIG 0.6BaM/0.4YIG
49.995 25.756 46.876 46.171 43.918 38.797
16.607 – 27.805 26.576 25.005 19.816
1635.4 – 2580.9 2436.1 2197.6 1933.6
of the individual phases. For isotropic two-phase composite, the small grain size improves both Hc and Mr [25]. In addition to this, there are two main interactions, exchange and dipolar interactions that determine the magnetic property of the two-phase composite. For the as-prepared BaM/YIG composites, at the low concentrations of soft YIG phase, the exchange interaction on the YIG magnetic moments excreted by the hard BaM phase is very strong, which results in the increase of Hc and Mr. With increasing the concentration of YIG, the exchange interaction on the YIG magnetic moments would be enervated and dipolar interaction among YIG grains becomes significant. Therefore the reverse domains in the YIG phase with low nucleation field could be nucleated easily, which causes the decrease of Mr and similar phenomenon also has been found in the BaFe12O19/Ni0.8Zn0.2Fe2O4 composite [19].
In order to evaluate the (BH)max of the BaM/YIG composites, Fig. 4(b) shows the magnetic hysteresis (B–H) loops of the purephase BaM, pure-phase YIG and BaM/YIG composites with different concentrations of YIG. The magnetic hysteresis (B–H) loops were transformed from magnetic hysteresis (M–H) loops, according to B = l0H + 4pM [26]. And the (BH)max values were calculated according to the demagnetization parts of the (B–H) loops. Fig. 4(c) presents the calculated magnetic energy products of the purephase BaM and BaM/YIG composites with different concentrations of YIG. It can be clearly seen that the values of (BH)max for all the BaM/YIG composites are much higher compared with that of the pure-phase BaM. The most important observation is that the 0.9BaM/0.1YIG composite exhibits a (BH)max value of 15.662 kJ/ m3. Hence, a giant enhancement of 290% of the (BH)max can be achieved. In order to further investigate the exchange coupling between the BaM phase and YIG phase, the demagnetization curves of hysteresis loops for the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites with different concentrations of YIG are compared in Fig. 5(a). Smooth demagnetization curves reflect exchange coupling phenomenon between different phases, and if exchange coupling does not exist among the phases in a composite system, the demagnetization curve in the hysteresis loop will present independent demagnetization of each phase [27], it can be seen that the 0.9BaM/0.1YIG composite exhibit a very smooth demagnetization curve, indicating that the BaM phase and the YIG phase are
Y. Lin et al. / Journal of Alloys and Compounds 641 (2015) 223–227
227
Fig. 5. (a) Demagnetization curves and (b) dM/dH of demagnetization curves of the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites with different concentrations of YIG.
very well exchange coupled for the 0.9BaM/0.1YIG composite. And with further increasing YIG concentration the demagnetization curve become more and more rough gradually, reflecting that the exchange coupling between the BaM phase and YIG phase decreases with increasing the concentration of YIG. Fig. 5(b) presents the dM/dH of demagnetization curves for the pure-phase BaM, the pure-phase YIG and the BaM/YIG composites. The dM/ dH of demagnetization curve is an indicative of exchange coupling interactions [3]. The appearance of peak at higher field for each curve is an indicator of the degree of exchange coupling between the two phases. The lower intensity of the peak shows the higher degree of exchange coupling. It can be seen that 0.9BaM/0.1YIG composite is not obvious, indicating very well exchange coupling between the BaM phase and YIG phase. With further increasing the concentration of YIG, the intensity of the peak increases, indicating that the exchange coupling of the BaM/YIG composites decrease with increasing the concentration of YIG. 4. Conclusions In conclusion, the BaM/YIG composites with giant enhancement of (BH)max were successfully synthesized by a simple sol–gel method. The XRD, SEM and EDS analysis reveal that the BaM and YIG phases can coexist with density and uniformly distribution. Magnetic property analysis of the BaM/YIG composites indicate that the BaM and YIG of the 0.9BaM/0.1YIG composite are well exchange coupled and the introduction of YIG could significantly enhance the Mr, Hc and (BH)max compared with pure BaM phase. Moreover, a giant 290% enhancement on (BH)max can be achieved compared with pure BaM phase. Additionally, this study indicates that exchange coupled composite with giant enhancement of Hc, Mr and (BH)max can be fabricated by simple chemical reaction and proper sintering process, which will be technologically important in future.
Technology Foundation of Shaanxi Province (Grant Nos. 2013KJXX79 and 2013JQ6004) and the Special Foundation of the Ministry of Shaanxi Province (Grant No. 2013JK0937) and the Scientific Research Starting Foundation of Shaanxi University of Science and Technology (Grant No. BJ13-13). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]
Acknowledgements [27]
This work is supported by the National Natural Science Foundation of China (Grant No. 51402178), the Science and
E.F. Kneller, R. Hawing, IEEE Trans. Magn. 27 (1991) 3588–3600. R. Skomski, J.M.D. Coey, Phys. Rev. B 48 (1993) 15812. D. Roy, P.S.A. Kumar, J. Appl. Phys. 106 (2009) 073902. X.J. Jiang, J.E. Shield, J. Magn. Magn. Mater. 333 (2013) 63–68. A.M. Belemuk, S.T. Chui, J. Appl. Phys. 113 (2013) 043913. J. Zhang, Y.K. Takahashi, R. Gopalan, K. Hono, Appl. Phys. Lett. 86 (2005) 122509. Z. Ahmad, S. Tao, T. Ma, G. Zhao, M. Yan, J. Alloys Comp. 509 (2011) 8952–8957. Y. Wang, Y. Huang, Q.F. Wang, J. Magn. Magn. Mater. 324 (2012) 3024–3028. M.A. Radmanesh, S.A.S. Ebrahimi, J. Magn. Magn. Mater. 324 (2012) 3094– 3098. L.Y. Zhang, Z.W. Li, J. Alloys Comp. 469 (2009) 422–426. S. Castro, M.G. Rivas, J.M. Greneche, J. Mira, C. Rodrlguez, J. Magn. Magn. Mater. 152 (1996) 61–69. L.C. Li, K. Chen, H. Liu, G.X. Tong, H.S. Qian, B. Hao, J. Alloys Comp. 557 (2013) 11–17. Z. Mosleh, P. Kameli, M. Ranjbar, H. Salamati, Ceram. Int. 40 (2014) 7279– 7284. K.S. Martirosyan, E. Galstyan, S.M. Hossain, Yi-Ju Wang, D. Litvinov, Mater. Sci. Eng., B 176 (2011) 8–13. V.V. Soman, V. Nanoti, D. Kulkarni, Ceram. Int. 39 (2003) 5513–5523. W. Zhang, C.J. Guo, R.J. Ji, C.X. Fang, Y.W. Zeng, Mater. Chem. Phys. 125 (2011) 646–651. J.W. Lee, J.H. Oh, J. Magn. Magn. Mater. 272 (2004) 2230–2232. S. Hazra, M.K. Patra, S.R. Vadera, N.N. Ghosh, J. Am. Ceram. Soc. 95 (2012) 60– 63. D. Roy, C. Shivakumara, P.S. Anil Kumar, J. Magn. Magn. Mater. 321 (2009) L11–L14. E.O. Hall, Proc. Phys. Soc. B 64 (1951) 747–753. S. Miglani, A.K. Jha, Mater. Res. Bull. 48 (2013) 1553–1559. S. Rhee, D. Agrawal, T. Shrout, M. Thumm, Ferroelectrics 261 (2001) 15–20. V.K. Sankaranarayanan, C. Sreekumar, Curr. Appl. Phys. 3 (2003) 205–208. A. Mergen, A. Qureshi, J. Alloys Comp. 478 (2009) 741–744. R. Fischer, T. Schrefl, H. Kronmüller, J. Fidler, J. Magn. Magn. Mater. 153 (1996) 35–49. X.Q. Liu, S.H. He, J.M. Qiu, J.P. Wang, Appl. Phys. Lett. 98 (2011) 222507– 222509. H. Zaigham, F.A. Khalid, J. Mater. Sci. Technol. 27 (2011) 218–222.