The thesis aims to produce nanoparticles (dielectric, ferrites, ferromagnetic, metal) and their nanoparticles. Find the optimal technology process, suitable for making absorbent samples. Survey the basic properties of fabricated nanomaterials. Measuring and studying the effects of microwave absorption in magnetic-dielectric nanoparticles, absorption mechanisms and dependence of absorbing properties on the parameters of materials, thereby finding solutions Enhance absorption capacity as well as adjust absorption parameters. Search and develop new materials with strong ability to absorb microwaves, catch up with world achievements.
MINISTRY OF EDUCATION VIET NAM ACADEMY OF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY …………… *****…………… CHU THI ANH XUAN SYNTHESIS AND STUDY OF MICROWAVE ABSORPTION OF La1.5Sr0.5NiO4 DIELECTRIC/FERROFERRIMAGNETIC NANOCOMPOSITE Specialized: Electronic materials Numerical code: 9.44.01.23 SUMMARY OF DOCTORAL IN MATERIALS SCIENCE Ha noi, 2018 The work is completed at: INSTITUTE OF MATERIALS SCIENCE - VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY Science supervisor: Dr Dao Nguyen Hoai Nam Prof Nguyen Xuan Phuc PhD dissertation reviewer 1: PhD dissertation reviewer 2: PhD dissertation reviewer 3: The thesis will be protected under supervisory board academy level at: Academy at … hours… day … month … 2018 People can find this thesis at: - National library - Graduate university of Science and Technology library LIST OF PROJECTS PUBLISHED Articles in the ISI directory: P.T Tho, C.T.A Xuan, D.M Quang, T.N Bach, T.D Thanh, N.T.H Le, D.H Manh, N.X Phuc, D.N.H Nam, “Microwave absorption properties of dielectric La1.5Sr0.5NiO4 ultrafine particles”, Materials Science and Engineering B, 186 (2014), pp 101-105 Chu T A Xuan, Pham T Tho, Doan M Quang, Ta N Bach, Tran D Thanh, Ngo T H Le, Do H Manh, Nguyen X Phuc, and Dao N H Nam, “Microwave Absorption in La1.5Sr0.5NiO4/CoFe2O4 Nanocomposites”, IEEE Transactions on Magnetics, Vol 50, No (2014), pp 2502804 Xuan T A Chu, Bach N Ta, Le T H Ngo, Manh H Do, Phuc X Nguyen, and Dao N H Nam, “Microwave Absorption Properties of Iron Nanoparticles Prepared by Ball-Milling”, Journal of Electronic Materials, Vol 45, No (2016), pp 2311-2315 T.N Bach, C.T.A Xuan, N.T.H Le, D.H Manh, D.N.H Nam, “Microwave absorption properties of (100-x)La1.5Sr0.5NiO4/xNiFe2O4 nanocomposites”, Journal of Alloys and Compounds, 695 (2017), pp 1658-1662 Articles published in domestic magazines: Chu Thị Anh Xuân, Phạm Trường Thọ, Đoàn Mạnh Quang, Tạ Ngọc Bách, Nguyễn Xuân Phúc, Đào Nguyên Hoài Nam, “Nghiên cứu khả hấp thụ sóng vi ba hạt nano điện mơi La1,5Sr0,5NiO4”, Tạp chí Khoa học Cơng nghệ, 52 (3B) (2014), tr 289-297 Chu Thi Anh Xuan, Ta Ngoc Bach, Tran Dang Thanh, Ngo Thi Hong Le, Do Hung Manh, Nguyen Xuan Phuc, Dao Nguyen Hoai Nam, “Highenergy ball milling preparation of La0.7Sr0.3MnO3 and (Co,Ni)Fe2O4 nanoparticles for microwave absorption applications”, Vietnam Journal of Chemistry, International Edition, 54(6) (2016), pp 704-709 Chu Thị Anh Xuân, Tạ Ngọc Bách, Ngô Thị Hồng Lê, Đỗ Hùng Mạnh, Nguyễn Xuân Phúc, Đào Nguyên Hoài Nam, “Chế tạo nghiên cứu tính chất hấp thụ sóng vi ba tố hợp hạt nano (100 x)La1.5Sr0.5NiO4/xNiFe2O4”, Tạp chí Khoa học Cơng nghệ - Đại học Thái Nguyên, 157(12/1), tr 177-181 Chu Thị Anh Xuân, Tạ Ngọc Bách, Đỗ Hùng Mạnh, Ngô Thị Hồng Lê, Nguyễn Xn Phúc, Đào Ngun Hồi Nam, “Tính chất hấp thụ sóng điện từ hệ hạt nano kim loại Fe vùng tần số vi ba”, Tạp chí Khoa học – Trường Đại học Sư phạm Hà Nội 2, Số 44 (2016), tr 16-23 9 Ta Ngoc Bach, Chu Thi Anh Xuan, Do Hung Manh, Ngo Thi Hong Le, Nguyen Xuan Phuc and Dao Nguyen Hoai Nam, “Microwave absorption properties of La1,5Sr0,5NiO4/La0.7Sr0.3MnO3 nanocomposite with and without metal backing”, Journal of Science of HNUE - Mathematical and Physical Sci., Vol 61(7) (2016), pp 128-137 Introduction In recent years, the electromagnetic radiation with the frequency in range of 1-100 GHz has great application in telecommunication, medical treatment, and military In company with that electromagnetic radiation also brings problems such as: electromagnetic interference, health diseases Therefore, developing absorbing materials, which has able to absorb electromagnetic radiation, have paid much attention in GHz frequency Microwave absorption materials (MAM) helps to prevent electromagnetic interference issue, reduce the cross-section reflectivity, and ensure the security of electronic systems Radar absorption materials (RAM) worked in frequency range of 8-12 GHz is widely used in military systems for stealth technology Generally, the study on electromagnetic absorption material mainly focuses on three ways: (1) preventing reflectivity signal, (2) enhancing the absorbability of material, and (3) extending frequency range The increase of loss tangent and absorption efficiency can be obtained if absorbing material can observe both electric and magnetic energy Moreover, nanotechnology provides the other ways to fabricate absorption material in nanoscale for shielding MAM with nano-size displays the improvement of absorption ability in comparison with micro-size Nanotechnology also helps to make the light weight and thin absorbed layer The microwave absorption ability of material can be determined by relative permeability (r), permittivity (r), and impedance matching between environment and material The reflection loss (RL) is used to determine the quality of MAM via the formula: RL = 20log|(Z - Z0)/(Z + Z0)|, where Z = Z0(r/r)1/2 is the impedance of material, Z0 is the impedance of air The maximum reflection loss can be obtained via two mechanisms: (i) the impedance of material equals to impedance of air, |Z| = Z0, which is so called Z matching; (ii) the thickness of absorbing layer satisfies the phase matching or quarter-wavelength condition (d = (2n+1)c/[4f(|r||r|)1/2], n = 0, 1, 2, …) Z matching normally achieves by balancing the permeability and permittivity values, r = r It can be obtained by fabricating a composite of dielectric and ferrite materials Recently, there are a lot of publications on MAM based on the nanocomposite of magnetic and dielectric materials in which the RL can be obtained below -50 dB The RL of nanocomposite is much higher than that of traditional materials such as carbon black-C and carbonyl-Fe If traditional materials provide the RL below -15 dB, the nanocomposite of ferrite and carbon give very deep RL below -50 dB For instance, a composite of Fe3O4/GCs shows RL around -52 dB at 8.76 GHz, or a composite of BaFe9Mn0.75Co0.75Ti1.5O19/ MWCNTs displays RL ~ -56 dB at 17 GHz It has been reported that a composite of C/CoFeCoFe2O4/paraffin is an excellent absorbing material with deep RL below 71.73 dB at 4.78 GHz The other core-shell composite Fe/HCNTs and coreshell Co-C in paraffin show the RL about – 50 dB and 62.12 dB at 7.41 GHz and 11.85 dB, respectively In Vietnam, the study on electromagnetic absorbing material started from 2011 by several group in military They show ability of nanocomposite of BiFeO3-CoFe2O4 (RL ~ -35.5 dB at 10.2 GHz) in X band The other nanocomposite Mn0.5Zn0.5Fe2O4 in resin and nano-ferrite Ba-Co have been also studied by them Besides, the studies on electromagnetic absorption of metamaterial and metamaterial cloaking by a group of Assoc Profs Vu Dinh Lam also show prominent results According to above reason, we propose a project “Synthesis and study of microwave absorption of La1.5Sr0.5NiO4 dielectric/ferro-ferrimagnetic nanocomposite” This proposal is used to replace the previous name “Synthesis and study of microwave absorption of ferroferrimagnetic/dielectric nanocomposite” We hope that our results contribute to the knowledge on electromagnetic absorbing material and develop the shielding and preventing EMI for electronic device This dissertation includes four chapter: Chapter Microwave absorption phenomena and materials Chapter Experimental Chapter Microwave absorption properties of dielectric La1.5Sr0.5NiO4 nanoparticles Chapter Synthesis and microwave absorption properties of iron nanoparticle Chapter Synthesis and microwave absorption properties of nanocomposite of dielectric with ferrite and ferromagnetic materials The main theme of dissertation: - Synthesis nanoparticle and nanocomposite of dielectric, ferrites, ferromagnetic, metal - Synthesis nanoparticle and nanocomposite of dielectric, ferrites, ferromagnetic, metal Studying the synthesis process and properties of materials - Studying the microwave absorption properties and absorption mechanism of ferromagnetic-dielectric nanocomposite - Finding new material for better absorption performance (RL ~ -40 dB - -60 dB) The object of thesis: - Ferromagnetic and ferrites nanoparticle with large µ and Ms, such as La0.3Sr0.7MnO3, CoFe2O4, NiFe2O4, and Fe - Colossal dielectric material La1.5Sr0.5NiO4 - Nanocomposite of ferro-ferrite and dielectric materials The methodology: This dissertation follows the experimental method According to the experimental data, we analyse the absorption properties of materials and compare with other reports Firstly, we synthesize material in nanoscale by high energy ball milling method combined with annealing in furnace at suitable temperature The crystal structure, morphology, and particle size have been analyzed by X-ray diffraction, scanning electron microscope The vibrating sample magnetometer (VSM) is used for investigation magentic properties of material Lastly, the measurement of the reflection and transmission of microwave is done in frequency – 18 GHz by free space method at room temperature The reflection loss can be calculated by transmission line and NRW method The experimental results is explained for the absorption properties of material The results of dissertation: The platelet of nanocomposite material with paraffin have been synthesized The large absorption ability of La1.5Sr0.5NiO4/paraffin has been reported for the first time in frequency – 18 GHz The RL reaches -36.7 dB, and the absorption efficiency closes to 99.98% The enhancement of resonance phase matching is observed for measuring absorption properties by reflection metal-back method The contrary behavior on the shifting of resonance peak of La1.5Sr0.5NiO4/NiFe2O4 and La1.5Sr0.5NiO4/La0.7Sr0.3MnO3 are observed As NFO and LSMO concentration increases, the absorption peak related to impedance matching tends to high-frequency shift for LSNO/NFO and lowfrequency shift for LSNO/LSMO This different behavior is believed origin from different absorption mechanisms The composite of LSNO/NFO follows the ferromagnetic resonance of NFO nanoparticle, while LSNO/LSMO relates to the ferromagnetic relaxation of LSMO nanoparticle In the process of working and writing this thesis, although the author has tried hard but still can not avoid the errors I wishes to receive the comments, the reviewer of the scientists as well as the people interested in the topic Chapter Microwave absorption phenomena and materials This chapter presents the researchs and developments of microwave absorption materials Some basic knowledge relates to the interaction between electromagnetic waves and materials, major absorption mechanisms occurring in absorbers, such as: electromagnetic loss in conductors, dielectric loss and magnetic losses have been presented to support discussions and explain experimental results in the following chapters This chapter also introduces some of the typical microwave absorption structures and materials, such as resonant absorption layer (Salisbury, Dallenbach), broadband absorption multilayer (Jaumann), inhomogeneous absorber, hybrid microwave absorption materials, magnetic absorbers or metamaterial perfect absorber and some of the specific materials related to the object of thesis (the dielectric material with colossal permittivity-La1.5Sr0.5NiO4, ferrite materials Ni(Co)Fe2O4 and ferromagnetic materials Fe, La0.7Sr0.3MnO3) based on the analysis of previous researched results This is important for discussing the researched results of thesis Chapter Experimental This chapter presents solid state reaction method combined with a highenergy ball milling technique and proper post-milling thermal annealing processes, allows preparing large amounts of high quality nanopowders required for microwave tranmission/reflection measurements Structure analysis techniques, elemental determination and magnetic properties measurements of materials have been effectively exploited to assess the quality of the product Some of electromagnetic parameters techniques of absorbers also introduce By using free-space transmission techniques, microwave transimission and reflection measurements in the air are carried out in the frequency range of 4-18 GHz This is the most suitable measurement method for investigating the microwave absorption capability of MAMs that are coated from a mixture of nanoparticles with paraffin on thin plates of mica The devices, which used in the experimental measurements of this thesis, are modern and high accuracy Finally, the impedance (Z) and the reflection loss (RL), which are characterized for both weak reflection and high absorption of MAMs, are calculated via the KaleidaGraph data processing software based on transmission line theory and NRW algorithm Chapter 3: Microwave absorption properties of dielectric La1.5Sr0.5NiO4 nanoparticles 3.1 Characteristics of dielectric La1.5Sr0.5NiO4 nanoparticles (103) 3.1.1 Crystal structure and particle size 30 40 50 60 70 (301) (224) (303/208) (310) (206) (118) (220) (211) (116) (204/107) (008/213) (200) (112) (004) (105) (114) (110) La1,5Sr0,5NiO4 80 M (emu/g) Figure 3.1 X-ray diffraction pattern Figure 3.2 SEM image of the LSNO of the LSNO powder at 300 K powder X-ray diffraction data (Fig 3.1) indicates that La1,5Sr0,5NiO4 particles are single phase of a tetragonal (F4K2Ni-perovskite-type, I4/mmm(139) space group) The nano particle size is about 50 nm The SEM images (Fig 3.2) indicates that the particle size is significantly larger than that obtained from the XRD technique, ranging from 100 nm to 300 nm 3.1.2 Magnetic properties 0.2 La1,5Sr0,5NiO4 Figure 3.3 shows the magnetization loop, M(μ0H), of 0.1 LSNO nanoparticles The result indicates very small magnetic moments with no hysteresis This -0.1 proves that the LSNO fabricated nanoparticles exhibit paramagnet-0.2 4 -1 10 -5000 5000 10 like behavior at room temperature H (Oe) 3.2 Microwave absorption capability of La1,5Sr0,5NiO4 Figure 3.3 Magnetic loop, M(H), of nanoparticles at different layers the LSNO material at room temperature thicknesses The characteristic parameters of La1,5Sr0,5NiO4/paraffin samples with 40/60 vol percentage, respectively, and different thicknesses, d = 1.5; 2.0; 3.0 and 3.5 mm are summarized in Table 3.1 The RL(f) and |Z|(f) curves are presented in Figures 3.4 (a)-(d) a) d = 1,5 mm -5 RL -15 fz2 -25 12 fz1 13 14 15 16 17 |Z| fz2 0.5 -25 0.4 377 12.5 13 13.5 -4 -20 RL (dB) 0.6 d = 3,5 mm -2 RL (dB) -15 fz1 0.2 12 11 |Z| (×10 ) 0.7 |Z| (×10 ) |Z| -30 12 10 d) 0.8 RL -10 0.4 f (GHz) d = 2,0 mm -5 377 0.9 b) fz1 -40 18 f (GHz) 0.6 RL -30 0.5 377 -20 0.8 -20 RL (dB) |Z| (×10 ) |Z| (×10 ) -10 -10 1.5 |Z| 1.2 d = 3,0 mm c) RL (dB) -6 RL |Z| -8 377 0.3 14 -10 f (GHz) 10 12 f (GHz) Figure 3.4 RL(f) and Z(f) curves of the LSNO/paraffin layers: (a) d = 1.5 mm; (b) d = 2.0 mm; d = 3.0 mm d = 3.5 mm Table 3.1 The microwave absorption characteristics for the paraffinmixed La1,5Sr0,5NiO4 particle layers with different thicknesses d (mm) 1.0 1.5 2.0 3.0 3.5 fr (GHz) - 14.7 12.18 9.7 8.2 fz1 (GHz) - 14.3 12.22 9.7 - fz2 (GHz) - 13.2 - 9.2 - fp (GHz) (n=1) 4.18 13.9 12.7 10.9 10.4 |Z”|(fz1)(Ω) - 209.5 34.6 18.5 - |Z”|(fz2)(Ω) - 317.2 - 242 - RL(fr)(dB) -24.5 -28.2 -36.7 -9.9 The RL(f) curves of d = 1,5; 2,0 3,0 mm samples in fig 3.4a-c exhibit a deep minimum peak in RL at fr that is close to the fz1 frequency (Tab 3.1), where the impedance matching condition (|Z| ≈ Z0 = 377 Ω) is satisfied This suggests that the strong microwave absorption at the minimum absorption notch would be attributed to a resonance caused by impedance matching (Zmatching) However, the resonance could also be caused by a phase 10 0 -1 -5 RL (dB) RL (dB) -2 -3 -4 -10 -15 -5 -6 -7 (a) 1,5 mm 2,0 mm 3,0 mm 3,5 mm -20 -25 14 (b) -8 1,5 mm 2,0 mm 3,0 mm 3,5 mm 10 12 15 16 17 18 f (GHz) f (GHz) Figure 4.4 RL(f) curves of Fe/paraffin sample with different thicknesses d in the frequency band (a) 4-12 GHz and (b) 14-18GHz These samples with thickness d = 1.5 mm; 2.0 mm and 3.5 mm (Fig 4.5) have |Z|/Z0 >2 value at the absorption peaks and thus not satisfy with impedance matching resonance However, for the sample with thickness d = 3.0 mm, impedance matching resonance |Z|/Z0 = determines the strong microwave absorption at the absorption peaks 0 a) d = 1,5 mm RL 3 -10 1,5 -15 -3 RL |Z| RL (dB) 2,5 |Z| (×10 ) |Z| -2 d = 3,0 mm c) -5 |Z| (×10 ) RL (dB) -1 -4 -20 -5 |Z| = 377 -25 -6 14 15 16 17 18 14 15 f (GHz) 15 16 f (GHz) 17 RL (dB) -4 -6 -8 -10 18 RL |Z| 3 -2 RL (dB) -6 |Z| (×10 ) |Z| (×10 ) RL |Z| -4 -8 14 18 d = 3,5 mm d) d = 2,0 mm -2 17 f (GHz) b) 16 0,5 14 15 16 17 18 f (GHz) Figure 4.5 The RL(f) |Z|(f) curves of samples with: (a) d = 1.5 mm; (b) d = 2.0 mm; (c) d = 3.0 mm and (d) d = 3.5 mm The value of the phase-matching resonance frequency (fp ~ 5.5 GHz) is very close to the absorbed peak frequency at the low frequency region of GHz (fr1) (Figure 4.4 and Tab 4.3), showing the resonance effect at the frequency region is determined by phase-matching 11 Table 4.3 The characteristic parameters of Fe/paraffin sheet d (mm) 1.5 3.5 fp(n = 2)(GHz) 5.5 5.6 5.4 5.6 fr1(GHz) 5.7 5.6 5.5 5.6 fr2(GHz) 15.6 15.6 15.6 15.5 RL(r1) -6.5 -6.4 -6 -5 RL(r2) -5.5 -6.9 -23 -9 RL(r1)(GHz) - Al -52.7 -44.6 -44.1 -13.2 RL(r2)(GHz) - Al -9.8 -7.7 -16.8 -13.5 1,2 1,5 mm 2,0 mm 3,0 mm 3,5 mm -20 0,6 RL (dB) 11 |S | 0,8 -10 0,4 -30 1,5 mm 2,0 mm 3,0 mm 3,5 mm -40 0,2 -50 (a) (b) -60 -0,2 f (GHz) 10 11 12 10 11 12 f (GHz) Figue 4.6 The dependence of | S11 | and RL to the frequency of the Fe / Paraffin samples with Al-balcked In order to better observe phase-matching in the low frequency region ~ GHz, microwave reflection mesuaments for Al-backed samples to enhance the intensity of the reflected wave from the back of the sample According to the results shown in Fig 4.6a, the phase-matching resonance in low frequency region ~ GHz is clearly illustrated by the strong decrease of the signal |S11| to zero and a corresponding absorption peak on the RL curve (f) (Fig 4.6b) In addition, the results show that the peak absorption move towards the low frequency region as d increases The microwave reflection measurements on metal backed samples could be used as a simple method to distinguish the phase-matching from the conventional Z-matching resonance 4.2.2 The effect of Fe and paraffin mass ratios on the microwave absorption properties of Fe/paraffin absorption layers 12 RL (dB) Figures 4.7 and 4.8 show RL(f) curve and the correlation between -2 the RL (f) and Z (f) curves of the -4 Fe/paraffin layers with a thickness -6 d = 3mm and r = mFe / mparaffin = -8 3/1; 4/1; 4.5/1 and 5/1 With mass 3/1 4/1 r= ratio r changes from 3/1 to 5/1, the 4,5/1 -10 5/1 samples exhibited weak -12 10 12 14 16 18 microwave absorption ability and f (GHz) did not significantly change in the Figure 4.7 The RL(f) curves for the frequency range The results also unbacked samples within the 4show that there is no clear 18GHz frequency range evidence of resonance can be observed in the whole range of frequencies The frequency values fp calculated according to the phase-matching model for the whole samples are listed in Table 4.4 0 a) r = 3/1 b) r = 4/1 -2 -2 RL Z/Z0 RL (dB) -6 Z/Z0 -6 0 Z/Z -4 -4 Z/Z RL (dB) RL -8 -8 -10 -12 -10 -1 c) -2 -3 -4 10 d) r = 4,5/1 -2 r = 5/1 RL Z/Z0 -5 -6 -7 -8 -6 0 -5 Z/Z0 Z/Z Z/Z -4 RL (dB) RL -3 RL (dB) -7 -8 12 13 14 f (GHz) 15 16 12 13 14 15 16 f (GHz) Figure 4.8 The RL(f) and Z(f) of Fe/paraffin absorption layers with mass ratio r: r = 3/1 (a); r = 4/1; r = 4.5/1 r = 5/1 Table 4.4 The fp calculation and observed value of all samples with different mass ratios r = mFe/mparaffin 3/1 4/1 4.5/1 5/1 fp(n = 2)(GHz) (tính tốn) 5.3 5.3 5.2 5.1 fp (GHz) (quan sát) 6.6 6.1 5.8 5.9 13 The results of the microwave reflectance measurement in the 4-18 GHz frequency band for Al-backed samples are shown in Figure 4.9 Figure 4.9a shows a strong decrease of the |S11| value around GHz This closes to the calculated values for phase-matching frequency fp in Table 4.4, which corresponding to the strong absorption peak on the RL (f) curve (Fig 4.9b) The RL reaches a large negative value of -56.7 dB at 5.4 GHz for r = 4.5/1 1.2 a) 10 b) 0.8 0.6 RL (dB) 11 |S | -10 0.4 0.2 10 12 f (GHz) 14 16 18 3/1 4/1 4,5/1 5/1 r= -50 -0.2 -30 -40 3/1 4/1 4.5/1 5/1 r= -20 -60 10 12 14 16 18 f (GHz) Figure 4.9 The absolute value of reflection coefficient | S11 | (a) and RL (f) (b) of all Fe / Paraffin absorption layers with an Al-plate 14 Chapter Synthesis and microwave absorption properties of nanocomposite of dielectric with ferrite and ferromagnetic materials 5.1 Synthesis and characteristics La0,7Sr0,3MnO3 materials of CoFe2O4, NiFe2O4 and 80 CoFe 2O4 (a) CoFe O anealled M (emu/g) 40 (40 (4 as-milled (2 Intensityđộ (arb.(đ.v.t.y) units) Cường 5.1.1 Ferrite CoFe2O4 nanoparticles -40 CFO-MK CFO-MB CFO-M900 bulk 30 40 50 60 2 (deg) 2θ (độ) 70 80 -80 -1.2 10 -8000 -4000 4000 8000 1.2 10 H (Oe) Figure 5.1 X-ray diffraction Figure 5.2 M(H) loops of the bulk, pattern of CFO annealed as-milled, and annealed nanopowder nanopowders of CFO The XRD data (Fig 5.1) indicate that the nanoparticle powders are single phase; all the diffraction peaks could be indexed to the expected crystal structures of inverse spinel cubic for CoFe2O4 The magnetization loops, M(H), for our CFO nanoparticles are shown in Fig 5.2 The CFO nanoparticles Table 5.1 The particle size , MS show typical hysteresis (at 10 kOe) and HC of samples characteristics with the saturation MS HC magnetization comparable to Samples (nm) (emu/g) (Oe) previously reported data for CFO CFO-MK 47.0 77 1000 nanoparticles prepared by other CFO-MB 26.3 56 3600 methods The characteristic 77 1500 parameters extracted from these CFO-M900 46.0 measurements are listed in Table 5.1 5.1.2 Ferrite NiFe2O4 nanoparticles Fig 5.3 presents the XRD patterns of the final NFO nanoparticle powders that were used to prepare for the absorbing plates The diffraction patterns show that they are single phase with no detectable secondary phase or impurity; all the peaks can be indexed to the expected crystal structures of spinel cubic for NFO 50 (a) NiFe O NiFe2O4 25 M (emu/g) annealed as-milled -25 (4 Intensity độ (arb units) Cường (đ.v.t.y) 15 30 40 50 NFO-MK NFO-MB NFO-M900 bulk 60 70 80 2 -50 -1.2 10 -8000 -4000 4000 8000 1.2 10 H (Oe) 2θ (độ) Figure 5.3 X-ray diffraction Figure 5.4 M(H) loops of the bulk, pattern of NFO annealed as-milled, and annealed nanopowders nanopowder of NFO Fig 5.4 presents the magnetic hysteresis loops,M(H), of the NFO bulk and nanoparticle powders before and after annealed The bulk NFO has a saturation magnetization Ms = 49 emu/g and coercivity Hc = 120 Oe However, due to the contribution from the surface disorder, surface roughness, and shape anisotropy, the as-milled powder has much smaller Ms and larger Hc than those of the bulk sample The characteristic parameters extracted from these measurements are listed in Table 5.2 Table 5.2 the crystal particle size , magnetization MS at 10 kOe and HC of samples MS (emu/g) Samples D (nm) HC (Oe) (Tại H = 10 kOe) CFO-MK 42.0 49.0 120 CFO-MB 23.2 34.5 967 CFO-M900 34.8 45.0 126 5.1.3 Ferromagnetic La0,7Sr0,3MnO3 nanoparticles Fig 5.5 presents the magnetic different forms: bulk, as-milled, and annealed nanopowder The saturation magnetization Ms (at H = 10 kOe) drops from 65.6 emu/g for the bulk to 36.2 emu/g for the nanoparticle powder as a result of damages caused by the milling This decrease in magnetization could be detrimental to the hysteresis loops, M(H), of LSMO in Table 5.3 The crystal particle size , magnetization MS at 10 kOe and HC of samples D MS HC Samples (nm) (emu/g) (Oe) LSMO-MK 54.5 65.6 5.0 LSMO-MB 32.3 36.8 23.0 LSMO-M900 38.6 53.2 13.0 16 absorbing capability of the nanoparticles However, an appropriate postmilling heat treatment would largely heal the damages and recover the magnetic characteristics Fig 5.6 presents the XRD patterns of LSMO nanoparticle powders The diffraction patterns show that they are single phase with no detectable secondary phase or possible impurity The characteristic parameters extracted from these measurements are listed in Table 5.3 80 LSMO-MK LSMO-MB LSMO-M900 La0,7Sr0,3MnO3 -80 -1 10 -5000 5000 10 20 30 40 50 60 70 (134) (128) (306) (220) (208) (024) LSMO-MK LSMO-MB LSMO-M900 (113) (202) (006) -40 (122) (116) (300) (018) (214) (110) (104) (012) M (emu/g) 40 80 H (Oe) Figure 5.5 Magnetic hysteresis Figure 5.6 X-ray diffraction M(H) loops of the La0.7Sr0.3MnO3 patterns of the La0.7Sr0.3MnO3 samples in different forms nanopowders 5.2 Microwave absorption capability of nanocomposites 5.2.1 The paraffin mixed (100-x)La1,5Sr0,5NiO4/xCoFe2O4 nanocomposites ( x = 0; 2; 4; 6; 8; 10) RL (dB) Fig 5.7 shows the RL(f) curves for all the unbacked samples in frequency range 4–18 GHz As expected, with doping CFO, the resonance notch in the RL(f) curves becomes deeper; the minimum RL decreases from −12.8dB for x=0 to −31.2 dB for x=8 Further increasing x leads to an abrupt increase of the minimum RL The decrease of RL with x for x≤8 should be attributed to the increase of magnetic loss and the balancing of permittivity and permeability caused by the substitution of CFO for LSNO nanoparticles The -10 -20 x= -30 6 10 10 12 14 16 18 f (GHz) Figure 5.7 Unbacked samples: RL of the (100−x)LSNO/xCFO absorbers within the frequency range of 4–18 GHz 17 characteristic parameters such as the resonance frequency f r extracted from these measurements are listed in Table 5.4 0 -2 1.6 -5 -5 RL (dB) 1.5 -15 0.5 10 11 12 13 14 15 -20 0.5 Z0 = 377 a) -14 b) -20 10 11 16 Z0 = 377 12 13 14 15 16 c) -25 11 12 17 -5 2.5 x=8 -5 1.6 RL (dB) 1.5 -20 0.4 0.5 -30 11 12 13 f (GHz) 14 15 16 Z0 = 377 -35 10 11 12 13 f (GHz) 14 15 16 1.5 -6 -8 0.5 -10 f) -12 10 11 Z0 = 377 12 13 14 15 16 17 f (GHz) Figure 5.8 Unbacked samples: enlargements of the RL(f) (right axis) and |Z/Z0|(f)(left axis) curves for all the samples in the resonance region near f =14 GHz (a)x =0, (b)x =2, (c)x =4, (d)x =6, (e)x =8, and (f) x=10 Table 5.4 Summary of the microwave absorption characteristics for the paraffin- mixed (100-x)LSNO/xCFO nanocomposites x (%) 10 a Unbacked fp (GHz) (n = 4.2 4.7 4.7 5.0 5.0 4.8 0) 12.0 12.0fz (GHz) 13.3 12.8 fr (GHz) 12.6 13.6 14.8 12.4 12.5 14.1 290 |Z’|( fr) (Ω) 39.2 320 RL(fr) (dB) -12.8 -17.8 -24.0 -21.3 -31.2 -10.8 b Al backed fr1 (GHz) 6.4 6.1 6.0 5.5 5.7 6.4 fr2 (GHz) 16.2 16.2 16.9 15.5 16.0 16.6 RL(fr1) (dB) -6.6 -15.5 -12.5 -54.3 -21.2 -25.5 RL(fr2) (dB) -6.8 -9.7 -11.2 -53.5 -10.5 -8.0 Z (k) 10 18 -4 -15 e) -25 17 -25 Z0 = 377 16 x = 10 Z (k) Z (k) 0.8 -15 15 -2 -10 1.2 -10 14 f (GHz) RL (dB) x=6 d) 13 0.4 0 Z0 = 377 f (GHz) f (GHz) -20 0.8 -15 -10 -12 1.2 -10 Z (k) -8 -10 Z (k) 1.5 RL (dB) -6 Z (k) RL (dB) x=4 x=2 2.5 -4 RL (dB) 2.5 x=0 18 In Fig 5.8, the resonance regionshows a zoomed-in view and RL(f) and |Z/Z0| curves for each sample are plotted together for comparison It is quite clear that the resonance occurs near the minimum of |Z/Z0| that is also close to The closer value of minimum |Z/Z0| to gives a smaller value of RL minimum; the deepest RL notch is observed for x =8 (Fig 5.8) where |Z/Z0| is found equal to This provides evidence for the main role of the Zmatching mechanism in these resonances According to (2), when perfect energy absorption or reflection cancelation occurs, Z =Z0 =1 and therefore RL = −∞ As mentioned above, although the calculations of fp suggest a phase matching of reflected waves at frequencies near GHz, no such resonance is observed The absence of the predicted resonance at the matching frequency could be caused by the fact that the samples are open circuited Without a metal backing plate, which is considered as a perfect reflector, the internal reflection wave on the reverse side would be much weaker than that on the incident side of the sample The cancelation of the two waves is therefore insignificant and phase-matching resonance may not be observed In order to further prove this assumption, reflection measurements for the corresponding samples with metal backing have been carried out; the results are shown in Fig 5.9 1.4 10 b) a) 1.2 -10 0.8 RL (dB) |S11| 0.6 10 0.4 x= 0.2 -20 -30 -50 -60 -0.2 10 12 f (GHz) x= -40 14 16 18 8 10 10 12 f (GHz) 14 16 18 Figure 5.9 Al-backed samples (a) Absolute value of the reflection coefficient, |S11| (b) RL of all the (100−x)LSNO/xCFO absorbers within the frequency range of 4–18 GHz Interestingly, the resonance around GHz is clearly shown by a sharp drop of |S11| [Fig 5.9(a)] and a corresponding notch in the RL(f)curve (Fig 5.9(b)) This observation not only proves the existence of the phasematching resonance near GHz, but also suggests a method to differentiate between the phase-matching and Z-matching resonances, both of them give zero reflection and |Z/Z0|=1 condition 19 RL (dB) 5.2.2 The paraffin mixed (100-x)La1,5Sr0,5NiO4/xNiFe2O4 nanocomposite (x = 0; 8; 15; 20; 30; 35) Fig 5.10 presents the RL(f) plots of the paraffin-mixed LSNO -5 and NFO nanopowder plates The NFO sample shows only weak -10 d = mm LSNO absorption (RL> -5 dB) and no NFO -15 indication of a resonance in the frequency range 4-18 GHz On the -20 10 12 14 16 18 other hand, the LSNO sample f (GHz) shows a clear deep notch in RL at fr Figure 5.10 RL(f) curves of ≈ 13.6 GHz that is close to the paraffin-mixed LSNO and NFO frequency fZ ≈ 13.7 GHz where the plates impedance |Z| ≈ Z0≈377Ω (Fig 5.11a) The deep notch in RL of the LSNO sample can therefore be attributed to an absorbing resonance caused by the effect of impedance matching The absorption of electromagnetic wave in LSNO is expectedly dominated by dielectric loss when the molecular dipoles are polarized at high frequency and energy of the microwave propagating through the material is dissipated via the dipole rotation The energy dissipation is maximized at the resonance frequency fr = fZ when the impedance matching condition is satisfied (b) x = RL (dB) RL (dB) -15 -10 -15 -20 -15 -20 10 12 14 16 -20 18 -30 f (GHz) 12 14 16 -25 18 (d) x = 20 5 -15 -10 -15 -20 Z0 = 377 -20 10 12 f (GHz) 14 16 18 2 -15 -20 -25 Z0 = 377 -30 10 12 f (GHz) 14 16 18 Z0 = 377 -25 10 12 14 16 f (GHz) Figure 5.11 RL(f) and |Z/Z0|(f) curves of the paraffin mixed (100x)LSNO/xNFO nanocomposite plates 18 Z (k) RL (dB) 18 -5 Z (k) Z (k) -10 16 (f) x = 35 -10 14 -5 -5 12 (e) x = 30 7 10 f (GHz) f (GHz) RL (dB) 10 Z0 = 377 Z0 = 377 RL (dB) 2 -25 Z0 = 377 Z (k) Z (k) Z (k) -10 -5 -10 (c) x = 15 -5 -5 RL (dB) 0 (a) x = 20 fr1 (Hz) 16 Fig 5.11 shows the RL(f) and |Zr/Z0|(f) curves of the paraffin mixed 15.5 (100-x)LSNO/xNFO nanocomposite 15 plates in the frequency range of 4- 18 14.5 GHz A summary of the characteristic 14 frequencies extracted from this figure (100-x)LSNO/xNFO 13.5 (100-x)LSNO/xLSMO is presented in Table 5.5 All the 13 10 15 20 25 30 35 40 samples show a sharp absorbing x (%) resonance at fr within the high Figure 5.12 The fr1(x) curves of frequency regime of 14-16 GHz LSNO/NFO and LSNO/LSMO Although the absorption is clearly nanocomposites stronger in the samples containing NFO, the variation of RLwith the NFO content x is not monotonous; RL reaches lowest values of -29.7 dB at x = and -28.5 dB at x = 30, respectively Since the NFO sample has only very weak absorption as shown in Fig 5.10, the improvement of absorption in the NFO-added samples would be associated with the dielectric-magnetic balancing rather than the direct contribution of magnetic loss from the added NFO nanoparticles Noticeably, despite the minimum of RL does not vary monotonously, the resonance frequency fr systematically shifts to higher frequency with increasing the NFO content: fr ≈13.6, 13.9, 14.7, 14.8, 15.3, and 15.9 GHz for x = 0, 8, 15, 20, 30, and 35, respectively For all the samples, since the f r matches very well to the frequency fZ where |Z/Z0| = 1, these observed resonances must be caused by the Z-matching effect Although the shift of fr (and fZ) with x could be a direct result of the dielectric-magnetic balancing caused by the doping of NFO, it is worth noting that it could also be caused by other effects, as will be discussed later In the present case, increasing NFO concentration is expected to enhance the interparticle coupling, which slows down the system's response, leading to a decrease in f0 In contrast, both fr and fZ, as shown in Fig 5.12, increase with x, thus ruling out the role of the relaxation mechanism One more possible mechanism that can be mentioned here is the well-known ferromagnetic resonance (FMR) absorption with the resonance frequency fFMR is given by: 𝑒 𝑓𝐹𝑀𝑅 = 𝛾𝐻𝑒𝑓𝑓 = 𝑔 (𝐻 + 𝐻𝐴 + 𝜇0 𝑀) (5.1) 2𝜋 2𝑚 Although, the FMR-based model could well explain the increase in the resonant frequency of our LSNO/NFO nanocomposites with increasing the NFO concentration, more experiments and analyses are still needed to verify 21 this possibility Based on the fact that fr is always close to fZ for all the samples, we propose that dielectricmagnetic balancing would be the most possible cause for its shifting with x In addition, the shift of the absorbing resonance toward higher frequency with increasing x would explain the result for NFO when fr and fZ become greater than the upper limit (18 GHz) of the measurements; far below fr and fZ, no significant absorption would be observed Table 5.5 Summary of the characteristic frequencies of the LSNO/NFO nanocomposite absorbing plates x (%) 15 20 30 35 fr (GHz) 13.6 13.9 14.7 14.8 15.3 15.9 fz (GHz) 13.7 14.2 14.7 14.7 15.4 15.7 fp-QS (GHz) 5.7 6.1 5.4 5.5 5.2 5.6 fp-TT (GHz) 5.9 5.8 5.7 5.7 5.5 5.3 1.2 a) b) 0.6 0.4 15 20 30 35 x= 0.2 RL (dB) |S11| 0.8 -5 -10 x= -15 15 20 30 35 -20 10 12 f (GHz) 14 16 18 10 12 14 16 18 f (GHz) Figure 5.13 |S11|(f) (a) and RL(f) of the Al-backed samples The phase matching effect is much enhanced by metal backing The results in Fig 5.11a-f also show that there exists a possible resonance with a notch in the low frequency range of 5-6 GHz Calculations of the phase matching frequency (Table 5.5), suggest that this notch could be indicative of a resonance caused by the phase matching effect if the phases of the reflected waves from both sides of the sample differ by π However, this observed phase matching resonance is quite weak, probably due to the incomplete cancellation of the reflected waves The reflection at the front surface would be much stronger than from the back To improve the backsurface reflection, the sample was attached on an Al plate and reflection measurement was then carried out The obtained reflection scattering parameter,|S11|, and reflection loss RL of the Al-backed samples are presented in Fig 5.13 As a result, the wave cancellation is much improved with the S11 signal drops close to zero and the RL lowers to below -10 dB 22 (-17 dB for x = 30) This result clearly verifies the phase-matching behavior of the resonance In addition, although the phase matching effect is enhanced by metal backing, due to the strong reflection by the backing plate, the Zmatching resonance near 16 GHz is strongly suppressed 5.2.3 The paraffin mixed (100-x)La1,5Sr0,5NiO4/xLa0,7Sr0,3MnO3 nanocomposite ( x = 0; 4; 8; 10) Figure 5.14 The RL(f) and |Z/Z0|(f) curves for all the samples in the frequency range of 4–18 GHz, (a) x = 0, (b) x = 4, (c) x = and (d) x = 10 Table 5.6 Summary of the microwave absorption characteristic parameters for paraffin mixed (100-x)La1.5Sr0.5NiO4/xLa0.7Sr0.3MnO3 nanocomposites x 10 a Unbacked samples fp (n=2) 5.3 5.27 5.26 5.16 fr1(GHz) 13.6 13.5 13.2 13.1 fr2(GHz) 5.7 5.57 5.8 5.53 RL(fr1)(dB) -18.2 -28.5 -16.9 -14.5 RL(fr2)(dB) -2.9 -2.7 -3.3 -2.9 b Al backed samples fr1(GHz) 15.9 15.4 16.6 fr2(GHz) 6.0 5.4 6.3 5.5 RL(fr1)(dB) -17.8 -8.7 -22.5 RL(fr2)(dB) -8.6 -30.7 -22 -53.8 23 Figs 5.14a-d present the RL(f) and Z/Z0(f) curves of all the (100x)LSNO/xLSMO samples A summary of the characteristic parameters extracted from these measurements are listed in Table 5.6 It is notable that all the samples exhibit a resonance notch in the RL(f) curves with a large negative value of RL at a frequency fr1 near 13 GHz Increasing the LSMO substitution enhances the absorbability for x < but degrades it for further substitution The lowest minimum value of RL of 28.5 dB is reached at the resonance Figure 5.15 Al-backed (100frequency fr1 ~ 13.6 GHz for the x)LSNO/xLSMO absorbers: (a) the absorption plate containing 4% reflection coefficient, |S11|, and (b) the vol of LSMO This result is quite corresponding RL close to those we have observed for (100-x)LSNO/xNFO where the lowest RL = -29.7 dB is found for x = As can be seen in the figures, the matching condition Z = Z0 is satisfied at frequency fZ fr1 for x = and x = 4, indicating that the resonance is associated with the Z-matching phenomenon For x > 4, the impedance Z gets closest to Z0 at the resonance but the Z-matching condition cannot be satisfied in the whole range of frequency Figs 5.15a,b show the frequency dependence of the reflection coefficient |S11| and RL of the Al-backed samples The influence of metal backing plate in the reflection measurements was also previously studied by Wang et al Notably, the |S11| signal drastically drops close to zero (Fig 5.15a) and correspondingly the resonance develops to a deep notch near GHz in the RL(f) curve The minimum RL reaches down to −53.8 dB at 5.5 GHz for x = 10 This result convincingly proves the phase-matching nature of the fr2 resonances Although metal backing could dramatically enhance the phase matching resonance, it suppresses the Z-matching effect by producing a strong reflection from the back side We therefore propose that using a metal backing plate in the reflection measurement is an effective method not only to prove the existence of the phase-matching, but also to distinguish the phase-matching and Z-matching resonances 24 Conclusions This dissertation study the microwave absorption of several nanoparticle and nanocomposite We have obtained several results listed below: The nanoparticle La1,5Sr0,5NiO4, CoFe2O4, NiFe2O4, La0,7Sr0,3MnO3, and Fe have been synthesized by solid state reaction method and high ball energy milling The effect of synthesis conditions on the properties of material have been studied We have developed a method to fabricate platelet composite of material and paraffin The absorption properties of platelet nanocomposite were measured by free space method to determine the transmission and reflection of microwave through the sample We use transmission line and NRW methods to analysis absorption data For the first time, we observed a strong microwave absorption of dielectric nanoparticle of La1,5Sr0,5NiO4 The absorption efficiency is about 99.98% The large absorption observed in colossal dielectric material is unexpected Our observation can promote the study on microwave absorption of colossal dielectric material The effect of thickness and material/paraffin volume ratio on the absorption properties have been investigated in systematic We developed the metal-back method for measuring microwave reflection signal This method allows to distinguish the resonance of phase matching and impedance matching We introduced a nanocomposite of ferromagnetic nanoparticle and dielectric nanoparticle This composite can enhance microwave absorption ability of (100-x) La1,5Sr0,5NiO4 + x(CoFe2O4; NiFe2O4; La0,7Sr0,3MnO3) Nanocomposite of ferromagnetic and dielectric material is a good way to enhance the absorption ability of MAM We have observed a contrary behavior on the shifting of resonance peak of LSNO/NFO and LSNO/LSMO As NFO and LSMO concentration increases, the absorption peak related to impedance matching tends to highfrequency shift for LSNO/NFO and low-frequency shift for LSNO/LSMO This different behavior is believed origin from different absorption mechanisms The composite of LSNO/NFO follows the ferromagnetic resonance of NFO nanoparticle, while LSNO/LSMO relates to the ferromagnetic relaxation of LSMO nanoparticle ... metal Studying the synthesis process and properties of materials - Studying the microwave absorption properties and absorption mechanism of ferromagnetic-dielectric nanocomposite 3 - Finding new... Synthesis and microwave absorption properties of iron nanoparticle Chapter Synthesis and microwave absorption properties of nanocomposite of dielectric with ferrite and ferromagnetic materials The main... electromagnetic absorption of metamaterial and metamaterial cloaking by a group of Assoc Profs Vu Dinh Lam also show prominent results According to above reason, we propose a project Synthesis and study of