Summary of Doctoral in Materials science: Synthesis and study of microwave absorption of La1.5Sr0.5NiO4 dielectric/ferroferrimagnetic nanocomposite

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

AND TRAINING

VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

……… *****………

CHU THI ANH XUAN

SYNTHESIS AND STUDY OF MICROWAVE

The work is completed at:

SCIENCE AND TECHNOLOGY

Science supervisor:

1 Dr Dao Nguyen Hoai Nam

2 Prof Nguyen Xuan Phuc

LIST OF PROJECTS PUBLISHED Articles in the ISI directory:

1 1 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

Science and Engineering B, 186 (2014), pp 101-105

2 2 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,

IEEE Transactions on Magnetics, Vol 50, No 6 (2014), pp 2502804

3 3 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 5 (2016), pp 2311-2315

4 4 T.N Bach, C.T.A Xuan, N.T.H Le, D.H Manh, D.N.H Nam,

nanocomposites”, Journal of Alloys and Compounds, 695 (2017), pp 1658-1662

Articles published in domestic magazines:

5 5 Chu Thị Anh Xuân, Phạm Trường Thọ, Đoàn Mạnh Quang, Tạ Ngọc Bách, Nguyễn Xuân Phúc, Đào Nguyên Hoài Nam, “Nghiên cứu khả năng

Khoa học Công nghệ, 52 (3B) (2014), tr 289-297

6 6 Chu Thi Anh Xuan, Ta Ngoc Bach, Tran Dang Thanh, Ngo Thi Hong

Le, Do Hung Manh, Nguyen Xuan Phuc, Dao Nguyen Hoai Nam,

nanoparticles for microwave absorption applications”, Vietnam Journal of Chemistry, International Edition, 54(6) (2016), pp 704-709

7 7 Chu Thị Anh Xuân, Tạ Ngọc Bách, Ngô Thị Hồng Lê, Đỗ Hùng Mạnh, Nguyễn Xuân Phúc, Đào Nguyên Hoài Nam, “Chế tạo và nghiên cứu tính chất hấp thụ sóng vi ba của tố hợp hạt nano (100 -

9 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

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

environment and material The reflection loss (RL) is used to determine the

maximum reflection loss can be obtained via two mechanisms: (i) the

Z matching; (ii) the thickness of absorbing layer satisfies the phase matching

Z matching normally achieves by balancing the permeability and

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,

dB at 17 GHz It has been reported that a composite of

-71.73 dB at 4.78 GHz The other shell composite Fe/HCNTs and shell 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

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

nanocomposite” This proposal is used to replace the previous name

ferro-ferrimagnetic/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 1 Microwave absorption phenomena and 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:

- 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 4 – 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 first time in frequency 4 – 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

NFO and LSMO concentration increases, the absorption peak related to impedance matching tends to high-frequency 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

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 1 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

results This is important for discussing the researched results of thesis

Chapter 2 Experimental

This chapter presents solid state reaction method combined with a energy 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

high-of MAMs that are coated from a mixture high-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

La 1.5 Sr 0.5 NiO 4 nanoparticles 3.1 Characteristics of dielectric La 1.5 Sr 0.5 NiO 4 nanoparticles

3.1.1 Crystal structure and particle size

Figure 3.1 X-ray diffraction pattern

of the LSNO powder at 300 K

Figure 3.2 SEM image of the LSNO

powder

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

LSNO nanoparticles The result

indicates very small magnetic

moments with no hysteresis This

proves that the LSNO fabricated

nanoparticles exhibit

paramagnet-like behavior at room temperature

capability of La 1,5 Sr 0,5 NiO 4

nanoparticles at different layers

thicknesses

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)

Figure 3.3 Magnetic loop, M(H), of

temperature

-0.2 -0.1 0 0.1 0.2

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 và d = 3.5 mm

Table 3.1 The microwave absorption characteristics for the

The RL(f) curves of d = 1,5; 2,0 và 3,0 mm samples in fig 3.4a-c exhibit

suggests that the strong microwave absorption at the minimum absorption

notch would be attributed to a resonance caused by impedance matching

(Z-matching) However, the resonance could also be caused by a phase

0.2 0.4 0.6 0.8 1 1.2

0 1 2 3 4

matching at f p frequency if the phases of the reflected waves from the two

sample’s surfaces differ by π:

It is difficult to determine conclusively which mechanism is responsible

resonance shifts to lower frequencies while the notch in RL, respectively,

becomes deeper (Fig 3.6) The resonance mechanic that is observed in this samples at minimum absorption peaks is the impedance mathching The

When the thickness is increased to 3.5 mm (Fig 3.4(d)), the microwave absorption is strongly suppressed No absorption notch could be observed at

backing plate will be drastically reduced the minimum values of RL or can

be broadened the resonance frequency region by combining the Z-matching

and phase- matching

Chapter 4 Synthesis and microwave absorption properties of iron

nanopaticles 4.1 The effect of fabricated conditions on the crystal structure, particle size and magnetic properties of Iron metal nanomaterials

The analysis of crystal structure

of Fe samples prepared for 1 to 20

appearance of diffraction lines

corresponding to the body-centered

cubic structure for α-Fe The

average particle size for all samples

are listed in Table 4.1 The

magnetization curve, M(H), at

sample (see the inset of Fig 4.2)

shows a high satutation moment

Ms and small coercivity Hc The

satutation magnetization of Fe powder decreased sharply after milling for 10 hours and then decreased slowly for longer milling time (Tab 4.1; Fig 4.2)

Figure 4.2 The dependence of Ms

on milling time and the M(H) cuver

of Fe-10h sample

Figure 4.3 The variability of Ms

(Fe-10h) following presered in air

Table 4.1 The average particle size D and the satutation magnetization Ms

at 10 kOe magnetic field of Fe powder after from 1h to 20h milling

keV

O |

Fe |

(b)

Figure 4.1 X-ray diffraction (XRD)

of iron samples after from 1-20h

milling

Fe-20h Fe-15h Fe-10h Fe-5h Fe-3h Fe-1h

(011)

Table 4.2 The satutation magnetization value (at 10 kOe) and % volume

of Iron oxide shell formation when Fe nano powder is preseved in air in

of the oxidation in the air of the samples after milling, magnetization

measurements were performed and monitored for the transformation of Ms

(t) for a long time after grinding The decrease of Ms saturation

magnetization value accoding to the preserved time (Figure 4.3 and Table 4.2) is considered as a result of the natural oxidation of the surface The

reduction rate of Ms after the milling time is almost proportional to the

spectral analysis (Fig 4.3) corresponded to the magnetic properties of Fe in the air In order to reduce the formation of oxide coatings surrounding Fe metal nanoparticles, the Fe/Paraffin adsorbing layers are spread out within

24 hours of grinding

4.2 The microwave absorption properties of the iron nanopaticles 4.2.1 The effect of absorbing layer thickness on the microwave absorption properties of Fe/paraffin

In this study, the absortion layer Fe/paraffin has got diffirent thichnees (d

= 1.5; 2; 3 và 3.5 mm) with % volume rate of Fe nano powder is 40% and paraffin is 60% The microwave absorption properties were measured into two modes: with Al-backed and unbacked sample

The RL (f) curve of the Fe/Paraffin absorption layers in the 4-18 GHz

frequency band is shown in Figure 4.4a-b Accordingly, the absorption peaks

is obtained for d = 3 mm thickness at ~ 15.6 GHz frequency, while the

remaining samples present a very weak microwave absorption ability with a value of RL> -9 dB At low frequencies near 6 GHz, the magnitude of the absorption peaks is approximately and the RL> -7dB represents the weak microwave absorption ability

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)

impedance matching resonance However, for the sample with thickness d =

microwave absorption at the absorption peaks

Figure 4.5 The RL(f) và |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 6

frequency region is determined by phase-matching

0 0,5 1 1,5 2 2,5

0 1 2 3 4