Magnetic and microwave absorption properties of rare earth ions (Sm3+, Er3+) doped strontium ferrite and its nanocomposites with polypyrrole

Magnetic and microwave absorption properties of rare earth ions (Sm3+, Er3+) doped strontium ferrite and its nanocomposites with polypyrrole

Journal of Magnetism and Magnetic Materials 381 (2015) 365–371 Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials...

1MB Sizes 0 Downloads 27 Views

Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

Contents lists available at ScienceDirect

Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm

Magnetic and microwave absorption properties of rare earth ions (Sm3 þ , Er3 þ ) doped strontium ferrite and its nanocomposites with polypyrrole Juhua Luo a,n, Yang Xu b, Hongkai Mao b a b

School of Materials Engineering, Yancheng Institute of Technology, Yancheng 224051, China School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013, China

art ic l e i nf o

a b s t r a c t

Article history: Received 15 January 2014 Received in revised form 28 August 2014 Accepted 11 January 2015 Available online 12 January 2015

M-type strontium ferrite substituted by RE (RE ¼Sm3 þ , Er3 þ ) were prepared via a sol–gel method. Polypyrrole (PPy)/ferrite nanocomposites (with 20 wt% ferrite) were prepared by in situ polymerization method in the presence of ammonium persulfate. Effect of the substituted RE ions on structure, magnetic properties and microwave absorption properties were investigated by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and vector network analyzer. All XRD patterns show the single phase of strontium hexaferrite without other intermediate phases. The crystallite size of synthesized particle is within the range of 22.2–38.1 nm. The structural in character of the composites were investigated with FT-IR analysis. It shows that the ferrite successfully packed by PPy. TEM photographs show that the particle size had grown up to 50–100 nm after coating with PPy. In the magnetization for the PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) composites, the coercivity (Hc) of the composites both increased compared with the undoped composite while the saturation magnetization (Ms) appeared opposite change with different RE ions. Considering the electromagnetic loss and impedance matching comprehensively, the Er-doped ferrite/PPy composite got the better microwave absorption performance with the maximum RL value of 24.01 dB in 13.8 GHz at 3.0 mm. And its width ( o  10 dB) has reached 7.2 GHz which has covered the whole Ku band. & 2015 Elsevier B.V. All rights reserved.

Keywords: Nanostructured materials Chemical synthesis Magnetic measurements

1. Introduction In recent year, conducting polymer as a kind of microwave absorption material has attracted intensive interests due to the growing demand of shielding against electromagnetic radiation in commercial, military, scientific electronic devices and communication instruments [1,2]. Among various organic polymer, polypyrrole (PPy) has been regarded as a representative material on account to its high electrical conductivity, easy preparation, and excellent environment stability [3,4]. But, polypyrrole can only absorb the electromagnetic waves generated by an electric source, whereas the electromagnetic from a magnetic source can be just shielded by magnetic materials [5]. Thus, it is still an emergency to investigate one kind of material which can shield electromagnetic wave both generated from magnetic and electric sources. Conducting polymer/ferrite nanoparticle composites provide an extraordinary access to solve this problem which combines the n

Corresponding author. Fax: þ 86 515 88298249. E-mail address: [email protected] (J. Luo).

http://dx.doi.org/10.1016/j.jmmm.2015.01.019 0304-8853/& 2015 Elsevier B.V. All rights reserved.

permeability (ferrite) and permittivity (conducting polymer) in composites. Also, the previous reports have demonstrated that incorporating ferrite and conducting polymer achieves great enhancement in microwave absorption properties. Yuan's group studied the polyaniline/SrFe12O19 composites, and the result showed that the conductivity of PANI on SrFe12O19 dramatically affected the microwave absorption properties [6]. Tang's group reported a composite of polyaniline-coated M–Ba-ferrite powders, the composite obtained improving microwave absorption properties due to the interaction and interfacial polarization between polyaniline and M–Ba-ferrite [7]. The polypyrrole/MnFe2O4 nanocomposite with core–shell structure were also synthesized, and the maximum reflection loss was  12 dB at frequency of 11.3 GHz [8]. M-type hexaferrite such as strontium ferrite is a promising microwave absorber and gets great concern in microwave absorption field because of its high magnetic loss and attenuated electromagnetic wave by the mechanism of magnetic hysteresis loss, domain-wall resonance, and natural resonance [6,7,9,10]. In addition, it is known to us the rare earth (RE) ions doped into

366

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

M-type strontium hexaferrite can not only determine the magnetocrystalline anisotropy in ferrite but also improve the electrical and magnetic properties. Because the RE ions have unpaired 4f electrons, the occurrence of 4f–3d couplings of the angular momentum which improve the electromagnetic properties. Moreover, 4f shell of rare earth ions is shielded by 5s25p6 and almost not affected by the potential field of surrounding ions leading to the enhancement of the coupling [11,12]. A large amount of work has been done to modify the electromagnetic properties of ferrites by substitution of Fe3 þ with rare earth element cations, such as La3 þ [13,14], Pr3 þ [11], Nd3 þ [15], Sc3 þ [16], etc. [17–23]. However, the composite of PPy/SrFe12O19 doped with rare earth element (RE¼ Sm and Er) in microwave absorption application has seldom reported so far. Therefore, in this article, we attempted to synthesize SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) nanoparticles by the sol–gel method and the PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) with 20 wt% ferrite was produced by in situ polymerization method. The magnetic performance and electromagnetic parameter of the samples were testified by VSM and vector network analyzer, respectively. And the structure and morphology were characterized by XRD, FT-IR and TEM. Furthermore, the different influence of doped Sm and Er on magnetic and microwave absorption properties was compared and the mechanism of RE enhancing magnetic properties and microwave absorption properties were explored in detail.

2. Experimental 2.1. Preparation of the samples 2.1.1. Preparation of Sm(Er) doped strontium ferrite nanoparticles Stoichiometric amounts of Sm(NO3)3(Er(NO3)3), Fe(NO3)3  9H2O and Sr(NO3)2 were dissolved in a minimum amount of deionized H2O by stirring at 40 °C with Fe/Sr ratio of 10.5. Citric acid was then added to the mixture solution to chelate these ions. The molar ratio of citric acid to metal ions of Sr2 þ and Fe3 þ was 1.5:1. Ammonia was added to adjust the pH value to 7. The clear solution was slowly evaporated at 70 °C under constant stirring, forming a viscous gel. By increasing the temperature up to 200 °C, the gel precursors were combusted to form loose powders. Finally, the obtained powder was calcined at 900 °C for 2 h. The SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) particles were thus obtained. 2.1.2. Preparation of PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) nanocomposite 1 ml Pyrrole monomer and certain amounts of SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) (account for 20 wt% of pyrrole quality) were added in 35 ml hydrochloric acid solution (0.1 mol L  1) and dispersed by ultrasonic wave for 30 min. 2.49 g of ammonium persulfate was a dissolved in 15 ml hydrochloric acid solution (1 mol L  1). The ammonium persulfate solution was then slowly added dropwise to the above mixture solution with vigorous stirring. The polymerization was carried out for 12 h. The composites were obtained by filtering and washing the reaction mixture with deionized water and ethanol and dried under vacuum at 60 °C for 24 h. PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) nanocomposite was thus synthesized. 2.2. Characterization The resulting powder was characterized by X-ray powder diffraction (XRD) using a diffractometer (RIGAKU, model D/max) with CuKα radiation of wavelength λ ¼0.154 nm. The crystallite size of synthesized ferrite particle is calculated by Scherrer formula:

D = 0.89λ /(β cos θ)

(1)

where λ ¼ 0.15406 nm, θ is the diffraction angle and β is the full width at half maximum (FWHM). The lattice constants of ferrite particle are calculated by using the following relation: 2 1 4 ⎛ h2 + hk + k 2 ⎞ ⎛ l ⎞ ⎟+⎜ ⎟ = ⎜ 2 2 3⎝ dhkl a ⎠ ⎝c ⎠

(2)

where (h k l) are Miller indices. The morphology of sample was studied with a transmission electron microscope (JEOL, model JEM 2001). Fourier transform infrared spectroscopy (FT-IR) for the prepared samples were carried out using the infrared spectrophotometer (NICOLET, model NEXUS 670) in the range from 4000 to 400 cm  1 with a resolution of 1 cm  1. Magnetization measurements were taken at room temperature (293 K) using a vibrating sample magnetometer (LDJ, model 9600-1). The complex permittivity (εr ¼ ε′  jε″) and permeability (μr ¼ μ′  jμ″) of the samples were measured by a microwave vector network analyzer (AGILENT, model N5244A) in the frequency range 2–18 GHz by using coaxial reflection/transmission technique (where the ε′, ε″, μ′ and μ″ is measured and the dielectric loss angle tangent (tan δε ¼ ε″/ε′) and the magnetic loss angle tangent (tan δμ ¼ μ″/μ′) were calculated by the measured parameters). The samples for vector network analyzer were pressed to be toroidal samples with OD 7 mm, ID 3.04 mm and height about 3 mm according to the mass ration 1:1 of paraffin and PANI/ SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) nanocomposite. Microwave absorption properties were evaluated by the reflection loss (RL), which was derived from the following formulas:

zin = z 0

μr εr

RL = 20 log

⎡ 2πfd ⎤ μ r εr ⎥ tanh ⎢j ⎣ c ⎦ zin − z 0 zin + z 0

(3)

(4)

where f is the frequency of incident electromagnetic wave, d is the absorber thickness, c is the velocity of light, Z0 is the impedance of free space, and Zin is the input impedance of absorber. The best absorbing properties is described by the impedance matching condition when Z0 ¼Zin. The  5 dB and 10 dB absorbing bandwidths mean that the frequency bandwidth can achieve 80% and 90% of reflection loss respectively.

3. Phase structure and composition analysis 3.1. XRD analysis Fig. 1 shows X-ray diffraction patterns of SrSm0.3Fe11.7O19 and SrFe11.7Er0.3O19. The obtained peaks are well matched with standard JCPDS card no. 33-1340. However, comparing to the inset of SrFe12O19, the diffraction peaks in SrRE0.3Fe11.7O19 ferrites appear to broaden as a results of incorporation of the rare-earth ions. Therefore, we can conclude that the phase structure of RE-doped strontium ferrite is M-type hexagonal ferrite and that RE ions does not change the crystal phase structure. The crystallite size of synthesized particle is within the range of 22.2  38.1 nm according to Scherrer formula. It is notable that the D (which is listed in Table 1) decreases with doped RE ions, which can be explained that RE ions may diffuse to the grain boundaries and have a segregation effect for the grains during the sintering process. This segregation process inhibits the grain growth by limiting grain mobility leading to the decrease of the crystallite size of RE-doped

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

SrSm0.3Fe11.7O19

367

SrFe12O19

20

25

30

35

40

45

(114)

25

30

45

50

55

55

60

65

70

(2 2 0 )

(2 0 1 2 )

(3 0 0 ) (2 1 7 ) (3 0 4 ) (2 0 1 1 )

(209)

(205)

40

(206)

(116)

(203)

35

50

2θ/°

(200) (201)

(008)

(110)

(107)

20

(1011)

Intensity/a.u.

SrEr0.3Fe11.7O19

60

65

70

2θ/° Fig. 2. XRD patterns of samples: (a) PPy, (b) PPy/SrEr0.3Fe11.7O19 and (c) PPy/SrSm0.3Fe11.7O19.

Fig. 1. XRD patterns of SrSm0.3Fe11.7O19 and SrEr0.3Fe11.7O19.

Table 1 X-ray diffraction data for the synthesized samples. Sample

SrFe12O19 SrSm0.3Fe11.7O19 SrEr0.3Fe11.7O19

Average crystallite size D (nm)

47.0 23.2 22.3

Lattice constant c/Å

a/Å

c/Å

22.78 23.87 22.91

5.83 5.84 5.84

3.91 4.09 3.92

ferrite [21]. The lattice constants of a and c are calculated from the value of interplanar spacing dhkl corresponding to the main peaks (107), (114) according to Eq. (2) and the values a and c are given in Table 1. These changes in the lattice constant may be caused by the different ionic radius of Sm3 þ (0.096 nm) (Er3 þ (0.088 nm)) and Fe3 þ (0.0645 nm) [13,21]. In practice, doping RE ions into ferrite is a process of forming solid solution. According to the previous literature [18,20,21], the doped RE ions prefer to replace Fe3 þ ions at octahedral site than other sites, which will lead to lattice parameter increase because of the bigger radii of RE ion than Fe3 þ ion. This accords with the results in our work listed in Table 1 which reveals that the doping by RE ions Sm(Er) is substituted into the crystal lattice without changing the magnetoplumbite structure of SrFe12O19. Fig. 2 shows the XRD patterns of the synthesized samples. Fig. 2a indicates that the peak located at 25.4° is the characteristic peak of PPy, which is ascribed to the perpendicular periodicity of polymer chain [24]. As can been seen in Fig. 2b and c, not only the characteristic peaks of the PPy appear, but also some other peaks are well scored with the date of PDF card of strontium hexaferrite. The intensities of SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) peaks in the composites are weaker than that of the pure ferrite, which reveal that the PPy coating layer has an effect on the peak intensity of SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) ferrite. Also, the result is similar to previous work [25,26] and it is evident that PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) composite is formed. 3.2. TEM analysis The surface appearance and microstructure of the SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) particles are characterized by

TEM. The TEM images of strontium ferrite doped by Sm(Er) are shown in Fig. 3a and b. It indicated that the particles obtained by sol–gel method are uniform in both morphology and particle size and the hexagonal structure of ferrite can be clearly observed. Although the grains are agglomerated to some extent, the particle sizes are in the range of 30–50 nm which is further supported by XRD analysis. Fig. 2c shows the SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) nanoparticles are dispersed in the PPy macromolecular matrix and the PPy continuously deposits on those nanoparticles surface where the black part is strontium ferrite and the light colored boundary is PPy in the composite according to the different electron penetrability. The particle sizes have grown up to 50  100 nm. The results of the TEM about the composites are consistent with XRD experimental. 3.3. FT-IR analysis Fig. 4 shows the FT-IR spectra of PPy, PPy/SrSm0.3Fe11.7O19 and PPy/SrEr0.3Fe11.7O19 composites. It can be observed from Fig. 4a and b that there is a weak peak at 600 cm  1 corresponding to vibrations of tetrahedral and octahedral sites for SrFe12O9 [7,24]. However, this peak cannot be observed in Fig. 4c and the PPy/SrSm0.3Fe11.7O19 (PPy/SrEr0.3Fe11.7O19) composite is almost identified by the characteristic peaks of PPy. The peaks at 1560 cm  1 and 1470 cm  1 are attributed to the characteristic C ¼C stretching of the quinoid and benzenoid rings [24], the peaks at 1299 cm  1 and 1240 cm  1 are corresponding to N–H bending and asymmetric C–N stretching modes of the benzenoid ring is also observed [27]. The broad peak around 1134 cm  1 is associated with vibrational modes of N¼ Q¼N (Q refers to the quinonic-type rings), and the peak at 815 cm  1 is assigned to the out-of-plane deformation of C–H in the p-disubstituted benzene ring [28] which indicating that PPy has formed in this sample. In addition, the peak located at about 3493 cm  1 corresponds to the N–H stretching mode [24,27]. These results of the PPy/SrSm0.3Fe11.7O19 (PPy/SrEr0.3Fe11.7O19) composites mean the PPy has succeeded packing on Sm(Er) doped strontium ferrite which are consist with XRD and TEM. Furthermore, there is an interaction between SrSm0.3Fe11.7O19 (PPy/SrEr0.3Fe11.7O19) particles and PPy chain which can be inferred by red shift peaks [25]. This interaction is caused by s–π interaction between ferrite and PPy, which included (1) the p molecular orbital of PPy overlapped where metallic empty d-orbital is the electron pair acceptor; (2) the πn

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

Transmittance /%

368

a b c

4000

3500

3000

2500

2000

1500

1000

500

Wavenumbers/cm-1 Fig. 4. FT-IR spectra of (a) PPy/SrSm0.3Fe11.7O19, (b) PPy/SrEr0.3Fe11.7O19, and (c) PPy.

8

Magnetization/emu·g-1

6 4

a

b

c

2 0 -2 -4 -6 -8 -15000

-10000

-5000

0

5000

10000

15000

Applied field/Oe Fig. 5. Magnetic hysteresis loops of (a) PPy/SrFe12O19, (b) PPy/SrSm0.3Fe11.7O19, and (c)PPy/SrEr0.3Fe11.7O19.

3.4. Magnetic properties Fig. 5 shows hysteresis loops of the synthesized samples which were carried out by VSM at room temperature with maximum applied field of 12,000 Oe. The magnetic characterization was texted in order to determine the effect of the Sm3 þ (Er3 þ ) substitution on the magnetic properties of PPy/SrSm0.3Fe11.7O19 (PPy/SrEr0.3Fe11.7O19) composites. The variation of saturation magnetization (Ms) and coercivity (Hc) of as-prepared sample is shown in Table 2, respectively. The Ms of PPy/SrSm0.3Fe11.7O19 declines compared with the PPy/SrFe12O19 composite while the Ms of Er doped composite increases. The decrease in magnetization with Sm element is due to the dilution of magnetization of B-sublattice by Sm3 þ ion [20]. The magnetic moment of Fe3 þ ion is 5 μB (3d5) with unpaired electron in d orbit [30], while the Fig. 3. TEM micrographs of (a) SrEr0.3Fe11.7O19, PPy/SrEr0.3Fe11.7O19, and (d) PPy/SrSm0.3Fe11.7O19.

(b)

SrSm0.3Fe11.7O19,

(c)

molecular orbital of PPy overlapped the d-orbital of metal ions to form the π-bond, in which the metal ions is electron pair donor [27,29].

Table 2 The room temperature magnetic parameters of as-prepared samples. Sample

Ms (emu g  1)

Hc (Oe)

PPy/SrFe12O19 PPy/SrSm0.3Fe11.7O19 PPy/SrEr0.3Fe11.7O19

4.56 2.79 6.54

6833.0 6929.8 6916.0

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

3.5. Electromagnetic parameter analyses As we all known that the dielectric loss angle tangent (tan δ) and the magnetic loss angle tangent (tan δμ) are vital parameters charactering the electromagnetic wave loss. It also has been reported that the electromagnetic wave losses of the conducting polymer/M-hexaferrite composites in 2–9 GHz depends on dielectric loss and when it goes to 9–18 GHz, the magnetic loss plays leading role [5,32]. Fig. 6 shows the magnetic loss tangent spectra of the synthesized samples. The results indicate that the curve b gets the maximum value of 0.13 at 12.5 GHz, curve c obtains the peak of 0.08 at 16.84 GHz, while the PPy/SrFe12O19 has the maximum loss at 0.10 in 16.76 GHz. Obviously, the magnetic loss of Er-doped

0.15 a b c

0.10

tan δμ

0.05

0.00

-0.05

-0.10 0

2

4

6

8

10 12 f /GHz

14

16

18

20

Fig. 6. The magnetic loss tangent of the samples as a function of frequency: (a) PPy/SrFe12O19, (b) PPy/SrEr0.3Fe11.7O19, and (c) PPy/SrSm0.3Fe11.7O19.

0.9 0.8 0.7

tan δε

magnetic moment of Sm3 þ ion contains two parts, orbital magnetic moment and spin magnetic moment. The orbital magnetic moment of Sm3 þ exists, because the radius ions of Sm3 þ is so large that crystalline field has not much stricture to Sm3 þ . Thus, the association of orbital magnetic and spin magnetic moment is 1.5 μB [19] which is far more less than the magnetic moment of Fe3 þ (5 μB) ion at B-site, leading to the attenuation in saturation magnetization for the Sm-substituted sample. The same mechanism also works to Er-substituted sample and the saturation magnetization enhances due to the 9.6 μB of Er3 þ [21] which is much higher than that of Fe3 þ (5 μB). Comparing with the undoped composite, the coercivity of the as-prepared samples doped by Sm3 þ and Er3 þ both increase and that of Sm3 þ doped sample is slight higher than that of Er3 þ doped sample. It is known that the grain boundary increased with a decrease in crystallite size [31]. According to the result of XRD, the crystallite size decreases with Sm(Er) doped sample. The area of disordered arrangement for atoms on grain boundaries may fix and hinder the domain wall motion, thus the coercivity of the doped composites increase [23]. Moreover, the more energy is need to make RE3 þ ions enter into lattice and form the bond of RE3 þ –O2  due to larger atomic radii as compared toFe3 þ ion (Sm3 þ 0.096 nm, Er3 þ 0.088 nm, Fe3 þ 0.0645 nm ) [20]. Therefore, energy for the Sm(Er)-doped samples to complete crystallization and grow grains is more, which makes domain wall motion becoming harder than undoped sample [23]. Taking the two sides into consideration, the Hc of RE doped samples increase and Sm-doped composite shows increasing Hc value as compared to that of Er-doped composite.

369

0.6 0.5

a b c

0.4 0.3 0.2

0

2

4

6

8

10

12

14

16

18

20

f /GHz Fig. 7. The dielectric loss tangent of the samples as a function of frequency: (a) PPy/SrFe12O19, (b) PPy/SrEr0.3Fe11.7O19, and (c) PPy/SrSm0.3Fe11.7O19.

composites is remarkably strengthened as compared to that of pure PPy/SrFe12O19 composite, meanwhile the magnetic loss Smdoped composites is weakened in 9–18 GHz. The magnetic loss tangent can be defined as tan δμ ¼ μ″/μ′. So the μ″ is closely related to the magnetic loss tangent. At the same time, the value of μ″ is in direct proportion to Ms according to the equation of μ″ ¼ Ms/(2Haα) (where Ms, Ha and α are saturation magnetization, anisotropy field and extinction coefficient, respective) [21]. According to the Ms value in Table 2, the change of tan δμ can be easily understood. Fig. 7 shows the dielectric loss tangent spectra of the synthesized samples. The results indicate that the dielectric loss is higher than the magnetic loss, and the maximum value goes to PPy/SrSm0.3Fe11.7O19 at 16. 96 GHz with value of 0.79. Also, the PPy/SrEr0.3Fe11.7O19 has a peak of 0.7 at 12.44 GHz while the PPy/SrFe12O19 reaches its maximum in 16.64 GHz with the value of 0.6. From Fig. 7, an almost overall upward trend of the dielectric loss angle tangent is observed in whole range of 2–18 GHz. It is reasoned that strontium ferrite turn into solid solution after being doped with small amounts of RE3 þ ion (Sm3 þ , Er3 þ ) which will cause the crystal cell of strontium expended. Then the intrinsic electric moment forms due to the large ionic radii of RE3 þ ion compared with that of Fe3 þ . Because the intrinsic electric moment occurs in the orientation polarization under external electric field, the dielectric loss improves [33]. In addition, the ionic radii of RE3 þ are greater than that of Fe3 þ , the substitution of RE3 þ for Fe3 þ induces lattice defects, which result in increasing dielectric loss [17]. In Sm-doped composite, the effect of orientation polarization is stronger than Er-doped composite on account of the ionic radii of Sm3 þ is longer than that of Er3 þ . In addition, according to the ferromagnetic resonance theory, the zero field ferromagnetic resonance frequency is expressed by the equation f = γHa/2π , where γ is the gyromagnetic ration and Ha is the magnetocrystalline anisotropy field [17]. Therefore, the f can be also expressed as this f = γMs/4παμ′′. So f is inversely related to μ″. On the basis of the above analysis, f can be adjusted by substituting Fe3 þ with different RE elements. So it provides a probability to realize the electromagnetic losses covers the whole frequency in 2–18 GHz. 3.6. Microwave absorption property Fig. 8 shows the frequency dependence of the reflection loss of the PPy/SrEr0.3Fe11.7O19 and PPy/SrSm0.3Fe11.7O19 composites at sample thickness of 2.0, 3.0, 4.0 mm. The Er-doped composite's

Reflectivity/dB

370

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

2 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 -28

doped. Generally, apart from dielectric loss and magnetic loss, another important concept relating to excellent microwave absorption is strongly dependent on the efficient complementarities between dielectric loss and magnetic loss [3,38], the single higher and lower dielectric loss or magnetic loss is harmful to the impedance match and results in strong reflection and weak absorption. The Sm-doped composite possesses the higher dielectric loss than that of Er-doped composite with the almost same magnetic loss, which gets worse impedance match leading to weak absorption performance. Therefore, the Er-doped composite is a better candidate for microwave absorption properties.

2mm 3mm 4mm

4. Conclusions

0

2

4

6

8

10 12 f /GHz

14

16

18

20

2

Reflectivity/dB

0

2mm

-2

3mm 4mm

-4

The Sm(Er)-doped nanometer size strontium ferrite particles were successfully prepared with the sol–gel and self-propagating method, the PPy/SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) with 20 wt% ferrite was successfully synthesized by an in situ polymerization. A series of characterization methods including XRD, FT-IR, TEM, VSM and Raman spectroscopy vector network analyzer indicated that the uniform SrSm0.3Fe11.7O19 (SrEr0.3Fe11.7O19) particles with the average size of 22.2–38.1 nm were packed by coating layer of PPy and the substituted RE ions had great influence on magnetic properties and microwave absorption performances. The PPy/SrEr0.3Fe11.7O19 composite possessed the best absorption property with the minimum RL value of  24.01 dB in 13.8 GHz at 3.0 mm and its width ( o 10 dB) reached 7.2 GHz which covered the whole Ku band due to the good impedance match of magnetic loss and electric loss making it a better microwave absorption absorber as compared to Sm-doped composite.

Acknowledgments

-6

-8

0

2

4

6

8

10

12

14

16

18

20

f / GHz

Authors are grateful to Key Laboratory for Ecological-Environment Materials and Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province of China and Qing Lan project for financial support for this research.

Fig. 8. The reflectance curves of the samples: (a) PPy/SrEr0.3Fe11.7O19 and (b) PPy/SrSm0.3Fe11.7O19.

References

best microwave absorption has reached  24.01 dB in 13.8 GHz with the thickness at 3.0 mm, while the Sm-doped just has got 7.56 dB in 15.36 GHz with 2.0 mm thickness. Moreover, for the Er-doped composite with the thickness of 4.0 mm, the reflection loss value less than  5 dB are obtained in the frequency of 6.04– 18 GHz which almost realizes the microwave absorption both in whole X and Ku wave band, even when the reflection loss value is less than  10 dB, the Er-doped composite can achieve the absorption range from 10.2 to 18 GHz with the thickness of 3.0 mm, which has covered the Ku wave band. And the Sm-dope composite also obtains the reflection loss value of less than  5 dB in same frequency. The Er-doped composite presents a better microwave absorption performance than single PPy [4], SrFe12O19 [34], SrFe12O19/PANI composite [6] BaFe12O19–Ni0.8Zn0.2 Fe2O4/PPy composite [35] and other PPy composite [8] because of the magnetic loss enhancing by Er-doping [36], originating from the spinrotation resonance of ferrite and interface relaxation between PPy and magnetic particle [35], and the dielectric loss of PPy with interfacial polarization relaxation effects and dipolar reorientation process [37]. It is interesting to discover that the microwave absorption property of Er-doped composite is much better than the Sm-

[1] M.K. Tehrani, A. Ghasemi, M. Moradi, R.S. Alam, Wideband electromagnetic wave absorber using doped barium hexaferrite in Ku-band, J. Alloy. Compd. 509 (2011) 8398–8400. [2] J. Sun, H.L. Xu, Y. Shen, H. Bi, W.F. Liang, R.B. Yang, Enhanced microwave absorption properties of the milled flake-shaped FeSiAl/graphite composites, J. Alloy. Compd. 548 (2013) 18–22. [3] P.B. Liu, Y. Huang, L. Wang, W. Zhang, Synthesis and excellent electromagnetic absorption properties of polypyrrole-reduced graphene oxide-Co3O4, J. Alloy. Compd. 573 (2013) 151–156. [4] D.A. Li, H.B. Wang, J.M. Zhao, X.L. Yang, Fabrication and electromagnetic characteristics of microwave absorbers coating PPy and Carbonyl iron composite, Mater. Chem. Phys. 130 (2011) 437–441. [5] Ö Yavuz, M.K. Ram, M. Aldissi, P. Poddar, D. Hariharan, Synthesis and the physical properties of MnZn ferrite and NiMnZn ferrite–polyaniline nanocomposite particles, J. Mater. Chem. 15 (2005) 810–817. [6] C.L. Yuan, Y.S. Hong, Microwave absorption of core–shell structure polyaniline/ SrFe12O19 composites, J. Mater. Sci. 45 (2010) 3470–3476. [7] X. Tang, Y.G. Yang, Surface modification of M–Ba-ferrite powders by polyaniline: towards improving microwave electromagnetic response, Appl. Surf. Sci. 255 (2009) 9381–9385. [8] S.H. Hosseini, A. Asadnia, Synthesis, and microwave-absorbing properties of polypyrrole/MnFe2O4 nanocomposite, J. Nanomater. 2012 (2012) 198973. [9] C.L. Yuan, Y.S. Hong, C.H. Lin, Synthesis and characterization of Sr (ZnZr)xFe12  2xO19-PANI composites, J. Magn. Magn. Mater. 323 (2011) 1851–1854. [10] A. Tadjarodi, H. Kerdari, M. Imami, Ba0.69Sr0.17Cd0.07Zn0.07Fe12O19 nanostrucutres/conducting polyaniline nanocomposites: synthesis, characterization and microwave absorption performance, J. Alloy. Compd. 554 (2013) 284–292. [11] S. Ounnunkad, Improving magnetic properties of barium hexaferrites by La or

J. Luo et al. / Journal of Magnetism and Magnetic Materials 381 (2015) 365–371

Pr substitution, Solid State Commun. 138 (2006) 472–475. [12] X.S. Liu, P. Hernández-Gómez, Y.X. Deng, K. Huang, X.B. Xu, S.X. Qiu, D. Zhou, Analysis of magnetic disaccommodation in La3 þ –Co2 þ -substituted strontium ferrites, J. Magn. Magn. Mater. 321 (2009) 2421–2424. [13] Y.Q. Li, Y. Huang, S.H. Qi, F.F. Niu, L. Niu, Preparation, and magnetic and electromagnetic properties of La-doped strontium ferrite film, J. Magn. Magn. Mater. 323 (2011) 2224–2332. [14] T.T.V. Nga, N.P. Duong, T.D. Hien, Synthesis of ultrafine SrLaxFe12  xO19 particles with high coercivity and magnetization by sol–gel method, J. Alloys Comp. 475 (2009) 55–59. [15] H. Yamamoto, M. Isono, T. Kobayashi, Magnetic properties of Ba–Nd–Co system M-type ferrite fine particles prepared by controlling the chemical coprecipitation method, J. Magn. Magn. Mater. 295 (2005) 51–56. [16] Z. Somogyvári, E. Sváb, K. Krezhov, L.F. Kiss, D. Kaptás, I. Vincze, E. Beregi, F. Bourèe, Non-collinear magnetic order in a Sc-substituted barium hexaferrite, J. Magn. Magn. Mater. 304 (2006) e775–e777. [17] C. Sun, K.N. Sun, P.F. Chui, Microwave absorption properties of Ce-substituted M-type barium ferrite, J. Magn. Magn. Mater. 324 (2012) 802–805. [18] S. Amiri, H. Shokrollahi, Magnetic and structural properties of RE doped Coferrite (RE ¼ Nd, Eu, Gd) nano-particles synthesized by co-precipitation, J. Magn. Magn. Mater. 345 (2013) 18–23. [19] M. Al-Haj, Structural characterization and magnetization of Mg0.7Zn0.3SmxFe2  xO4 ferrite, J. Magn. Magn. Mater. 299 (2006) 435–439. [20] J. Jiang, L.C. Li, F. Xu, Y.L. Xie, Preparation and magnetic properties of Zn–Cu– Cr–Sm ferrite via a rheological phase reaction method, Mater. Sci. Eng. B 137 (2007) 166–169. [21] X.G. Huang, J. Zhang, H.Z. Wang, S.T. Yan, L.X. Wang, Q.T. Zhang, Er3 þ -substituted W-type barium ferrite: preparation and electromagnetic properties, J. Rare Earth 28 (2010) 940–943. [22] J.H. Luo, Structural and magnetic properties of Nd-doped strontium ferrite nanoparticles, Mater. Lett. 80 (2012) 162–164. [23] L.J. Zhao, H. Yang, L.X. Yu, Y.M. Cui, Effects of Gd2O3 on structure and magnetic properties of Ni–Mn ferrite, J. Mater. Sci. 41 (2006) 3083–3087. [24] Q.L. Li, C.R. Zhang, Y.X. Wang, B.D. Li, Preparation and characterization of flakelike polypyrrole/SrFe12O19 composites with different surface active agents, Synth. Met. 159 (2009) 2029–2033. [25] C.R. Zhang, Q.L. Li, Y. Ye, Preparation and characterization of polypyrrole/nanoSrFe12O19 composites by in situ polymerization method, Synth. Met. 159 (2009) 1008–1013. [26] Z.Y. Peng, J.P. Fu, L. Luo, F.L. Huang, Q.F. Wei, Fabrication of PA6/TiO2/PANI

[27] [28]

[29]

[30]

[31]

[32]

[33] [34]

[35]

[36]

[37]

[38]

371

composite nanofibers by electrospining-electrospraying for ammonia sensor, Colloids Surf. A 461 (2014) 113–118. P.H. Qiao, B.B. Zhao, Z.D. Nan, Facile fabrication of ZnLa0.02Fe1.98O4/PPy and application in water treatment, Mater. Sci. Eng. B 178 (2013) 1476–1482. H.C. Kand, K.E. Gecheler, Enhanced electrical conductivity of polypyrrole prepared by chemical oxidative polymerization: effect of the preparation technique and polymer additive, Polymer 41 (2000) 6931–6934. Y.P. Wang, L.C. Li, J. Jiang, H. Liu, H.Z. Qiu, F. Xu, Conductivity and magnetic properties of Zn0.6Cu0.4Cr0.5La0.04Fe1.46O4/PPy, React. Funct. Polym. 68 (2008) 1587–1593. B.K. Rai, S.R. Mishra, V.V. Nguyen, J.P. Liu, Influence of RE3 þ co-substitution on the structure and magnetic properties of Sr0.82RE0.18Fe12O19 (RE:La0.18  xPrx) ferrites, J. Alloy. Compd. 581 (2013) 275–281. F. Muthafar, S. Al-Hilli, K.S. Li, Kassim, Structural analysis, magnetic and electrical properties of samarium substituted lithium–nickel mixed ferrite, J. Magn. Magn. Mater. 324 (2012) 873–879. Y.Q. Li, Y. Huang, S.H. Qi, L. Niu, Y.L. Zhang, Y.F. Wu, Preparation, magnetic and electromagnetic properties of polyaniline/strontium ferrite/multiwalled carbon nanotubes composite, Appl. Surf. Sci. 258 (2012) 3659–3666. X. Ren, G.L. Xu, Electromagnetic and microwave absorbing properties of NiCoZn-ferrites doped with La3 þ , J. Magn. Magn. Mater. 354 (2014) 44–48. M. Jamalia, A. Ghasemi, E. Paimozd, A comparison of the magnetic and microwave absorption properties of Mn–Sn–Ti substituted strontium ferrite with and without multi-walled carbon nanotube, Curr. Appl. Phys. 14 (2014) 909–915. Y. Wang, Y. Huang, Q.F. Wang, Q. He, L. Chen, Preparation and electromagnetic properties of polyaniline (polypyrrole)-BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite nanocoposites, Appl. Surf. Sci. 259 (2012) 486–493. J. Wang, H. Zhang, S.X. Bai, K. Chen, C.R. Zhang, Microwave absorbing properties of rare-earth elements substituted W-typed barium ferrite, J. Magn. Magn. Mater. 317 (2007) 310–313. L.C. Li, C. Xiang, X.X. Liang, B. Hao, Zn0.6Cu0.4Cr0.5Fe1.46Sm0.04O4 ferrite and its nanocomposites with polyaniline and polypyrrole: preparation and electromagnetic properties, Synth. Met. 160 (2010) 28–34. Y.J. Chen, P. Gao, C.L. Zhu, R.X. Wang, L.J. Wang, M.S. Cao, X.Y. Fang, Synthesis, magnetic and electromagnetic wave absorption properties of porous Fe3O4 /Fe/SiO2 core/shell nanorods, J. Appl. Phys. 106 (2009) 054303.