Journal of Physics and Chemistry of Solids 73 (2012) 478–483

Contents lists available at SciVerse ScienceDirect

Journal of Physics and Chemistry of Solids

0022-36

doi:10.1

n Corr

E-m

journal homepage: www.elsevier.com/locate/jpcs

Preparation and characterization of iron/titanium-oxide composite particles

Xin Tang a,n, Jin Huang b, Linjie Kang b, Chang Nie b, Xing Lin b

a State Key Lab of OGRGE, Southwest Petroleum University, Chengdu 610500, PR Chinab Graduate School, Southwest Petroleum University, Chengdu 610500, PR China

a r t i c l e i n f o

Article history:

Received 29 March 2011

Received in revised form

23 July 2011

Accepted 22 November 2011Available online 1 December 2011

Keywords:

A. Magnetic materials

B. Chemical synthesis

C. Mossbauer spectroscopy

D. Magnetic properties

97/$ - see front matter & 2011 Elsevier Ltd. A

016/j.jpcs.2011.11.030

esponding author.

ail address: rivertx2003@yahoo.com.cn (X. Ta

a b s t r a c t

The iron/titanium-oxide composite particles have been prepared using ‘‘in-situ’’ hydrogen-thermal

reduction method. The composites were characterized by X-ray diffraction, physical property measure-

ment system and Mossbauer spectroscopy. The powder X-ray diffraction patterns reveal the presence

of crystalline a-iron and titanium-oxide (FeTiO3/TiO2). The Mossbauer spectra of powders have been

measured at room temperature, which indicated that the a-iron and the high-spin iron(II/III)

components were observed. The complex permittivity and permeability of the composites have been

measured using vector network analyzers. Reflection loss of the iron/titanium-oxide composite

powders dispersing in epoxy resin has been calculated using measured values of complex permittivity

and permeability in the frequency range of 2–12 GHz. The maximum reflection loss of �36 dB was

observed at 5.0 GHz. This study shows the possibility to obtain the novel dielectric and magnetic based

microwave absorbers.

& 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Due to the rapid development of electronic and telecommunica-tion systems, there is an increasing interest in shielding againstelectromagnetic radiation in commercial, military, scientific electro-nic devices and communication instruments. The most effectivesolution to this problem is the use of microwave absorptionmaterials. These materials, including oxides, alloy–epoxy compo-sites and metallic magnetic materials, have aroused particularinterest of many researchers because of their desirable complexpermeability (m0 � jm00) and permittivity (e0 � je00), which determinethe reflection and attenuation characteristics [1,2].

Metallic magnetic materials have high saturation magnetiza-tion and excellent magnetic properties, which make it potentialgood magnetic loss materials in a high frequency such as X band[3–5]. However, there are many problems when metallic mag-netic materials are used as fillers in microwave absorber. First, theelectrical conductivity of these materials is generally high, so thatthe high-frequency magnetic permeability decreases due to theeddy current loss induced by the electromagnetic wave. Second,the complex dielectric permittivity is too large, which increasesthe reflection coefficient of the absorber owing to a largedifference in the values of the magnetic permeability and dielec-tric permittivity. In view of the reasons mentioned above, it isnecessary to decrease the conductivity of metal magnetic

ll rights reserved.

ng).

materials. Ferromagnetic particles dispersed in an insulatingmatrix have been reported [6]. Previous authors have reportedthat the amorphous-carbon or rare-earth oxides can be usedas separator in reducing the complex relative dielectricpermittivity [7].

Dielectric materials have a broad loss spectrum in GHz frequen-cies due to domain wall vibration or dynamic behavior of polarclusters, and dielectric loss of those pervoskite ferroelectric ceramicsis high in the frequency range of 0.1–10.0 GHz [8]. The dielectricceramics can, therefore, be a good absorption material in GHzfrequencies. As an important dielectric material, titanium-oxidehas high dielectric permittivity and high dielectric losses in themicrowave frequency region. Pinho et al. [9] have investigated theeffects of barium and strontium titania on the microwave reflectivityproperties of iron and ferrite materials.

However, it is very important to note that pure dielectric ormagnetic materials absorb radiation energy insufficiently. Theefficiency of magnetic–dielectric absorbers is high because thecomplex permittivity (er¼e0 � je00) and permeability (mr¼m0 � jm00)differ from unity. As a result, the materials’ thickness decreases by(e0m0)1/2 times [10,11]. Extensive study has been carried out todevelop new electromagnetic wave absorption materials with ahigh magnetic and electric loss [12–16].

The composite approach has been used to improve variousmaterial properties including mechanical, chemical, structural,optical and electrical/magnetic properties. In this research, theconcept of composite is used to develop a novel microwaveabsorption material. Titanium-oxide/iron composites combinethe advantages of dielectric and magnetic absorption materials,

X. Tang et al. / Journal of Physics and Chemistry of Solids 73 (2012) 478–483 479

which enable us to tailor the material properties according toeach application. These factors motivate us to work on thesynthesis of titanium-oxide/iron composites suitable for micro-wave absorption application. Our group focused on the ‘‘in-situ’’formation of a type of magnetic–dielectric composites, which aremade up of titanium-oxide and iron fine particles.

The ‘‘in-situ’’ synthesis method is a relatively novel and simpleroute for the preparation of a great number of composites, somany investigators have adopted it [17–19]. In comparison withthe conventional composite, it exhibits the following advantages:(a) the in situ formed composites are finer in size and the particlesare evenly distributed; (b) the component interfaces areenhanced, resulting in a strong interfacial electromagnetic/mag-netic interaction. So far, no study on the preparation and char-acterization of iron/titanium-oxide composites has been reported.In this paper, we reported on ‘‘in-situ’’ preparation of a novel iron/titanium-oxide composite, and investigated on the influences ofthe reduction reaction time on the composition, crystal structure,magnetic property and electromagnetic parameters of iron/tita-nium-oxide composites in the frequency range of 2�12 GHz.Based on the model of a single layer absorber backed by a perfectconductor, absorption spectra have been theoretically predicted.

Fig. 1. TG/DTA curves of the dried precursor.

2. Experimental

2.1. Preparation of the composite samples

In this study, ferrite nitrate, tetrabutyl titanate, anhydrousethanol, ammonia solution and acetylacetone were used as thestarting materials. Double distilled water was used as a solvent.All reagents supplied by the Sinopharm Group Chemical ReagentShanghai Limited Company (China) were of analytical grade, andwere used without further purification. In a typical procedure,0.05 mol of tetrabutyl titanate was first dissolved in 30 ml anhy-drous ethanol with acetylacetone under vigorous stir for 30 min.0.05 mol of ferrite nitrate was dissolved into 15 ml deionized waterand 20 ml of anhydrous ethanol. Subsequently, two solutions weremixed under vigorous stir at room temperature for 2 h to obtain awell dissolved solution. Finally, the solution was evaporated at roomtemperature to allow the gel formation and dried in oven at 75 1Cfor 24 h. The dried precursor was ground to break up largeagglomerates. Based on the thermogravimetric-differential thermalanalysis, the dried precursor was calcined in the horizontal quartztube furnace at 550 1C for 2 h in the flowing air to remove organics,and subsequently reduced at 650 1C for different time in a flow ofH2. Hydrogen flow was maintained until the furnace reached roomtemperature to avoid the oxidation of the reduced samples duringthe cooling of the furnace. The prepared powders were stored forfurther characterization after the sintering and reduction processes.

2.2. Characterization

In order to determine the temperature of possible decomposi-tion, the dried precursor was subjected to thermogravimetric-differential thermal analysis. The analysis was carried out in aDupont Model 950 thermoanalyzer with DTA and TG stages;specimens were annealed in flowing air from 50 to 800 1C at20 1C/min. The final product obtained was a lustrous blackpowder. FT-IR spectra of species in the IR range of 400–4000 cm�1 were measured by FT-IR spectrometer (Equinox 55,Bruker Analytische Messtechnik GmbH). The crystal structures ofthe samples were analyzed at room temperature (RT) by powderX-ray Diffraction (XRD) using a Bruker AXS D8 Advance diffract-ometer with the wavelength of 1.5418 A of CuKa radiation in therange 2y¼10–901. Mossbauer spectroscopy was used in order to

obtain the hyperfine parameters of the powders. Mossbauerinvestigations were carried out by the use of transmissionspectrometer arranged in vertical geometry, 57Co(Pd) source ofgamma radiation and a drive system working in a constantacceleration mode. The velocity scale was calibrated with a pureiron foil. The specific saturation magnetization of the particleswas measured by means of physical property measurementsystem (PPMS-9, America) at a maximum applied field of10 kOe at room temperature. A network analyzer (Agilent Tech-nologies, E8363A) was employed to determine the values of thecomplex permittivity (er¼e0 � je00) and permeability (mr¼m0 � jm00)at the frequency range of 2–12 GHz using coaxial reflection/transmission technique. For this, the samples were prepared with80% (weight percentage) powder loading in epoxy resin, and thetoroidal shaped samples of 3.0 mm inner diameter, 7.0 mm outerdiameter and 3–4 mm length were prepared. The test samples oftoroidal shape were tightly inserted into the standard coaxial line,the measured values of the complex permittivity (er¼e0 � je00) andpermeability (mr¼m0 � jm00) were used to determine microwavereflection loss [20].

3. Results and discussion

3.1. TG-DTA analysis

TG and DTA measurements were performed to study thethermal behavior of the precursor, and the respective curves areshown in Fig. 1. It can be seen that in the temperature region 50–150 1C, an endothermic peak with a weight loss appeared, whichcan be assigned to the removal of the solvent and inner water inthe precursor. The weight loss corresponding to a strongerexothermic peak at about 187 1C is mostly due to the burning ofthe carbon based materials from alkoxide, solvent and chelatingagent in the precursor. During the burning process, many gasesare emitted, such as H2O and CO2 from the precursor. Anotherabrupt weight loss occurs near 250 1C, which ends at about400 1C. The DTA curve indicates that the strongest exothermicpeak is at about 260 1C, which is related to the oxidation ofresidual organics.

3.2. FT-IR spectrum

To determine the changes in chemical environment of thesamples, the FT-IR spectra taken over a wave number of 400–4000 cm�1 for the dried precursor and precursor annealed at550 1C for 2 h are recorded and shown in Fig. 2. The spectrum of

Fig. 2. FT-IR spectra of (a) the dried precursor and (b) heat treated precursor.

Fig. 3. X-ray diffraction analysis for the prepared powder reduced at 650 1C at

different reduced reaction time.

X. Tang et al. / Journal of Physics and Chemistry of Solids 73 (2012) 478–483480

the dried precursor (see Fig. 2(a)) clearly shows a broad absorp-tion around 3410 cm�1, which is a characteristic stretchingvibration of hydroxylate (O–H) [21]. Two small peaks at 2920and 2849 cm�1 are attributed to the stretching vibrations of –CH2

and –CH3. Peaks localized at 1560 and 1390 cm�1 are assigned toasymmetrical and symmetrical stretching vibration of carboxylate(O–C¼O), respectively. For the dried precursor, C–O stretchingvibration of C–OH at 1080 cm�1 is observed. The characteristicbands of nitrate ions are not detected, indicating that anoxidation–reduction reaction occurred during drying process.During the reaction, nitrate ions act as oxidizers and the carboxylis the reducing agent. Peaks localized at 796 and 643 cm�1 areassigned to the deformation vibration of the C–H group. It couldbe concluded that Fe–Ti–citrate complex was formed in thesolution. Obviously, after heating the precursor (refer toFig. 2(b)), the functional groups of COO� have been decomposed.The new band at 518 cm�1 should be ascribed to metal–oxygenstretching vibration of heated powders. However, slight absorp-tion bands of hydroxylate and carbonate remain.

3.3. X-ray diffraction

The XRD patterns are shown in Fig. 3(a–e) for samples of the heattreated precursor powder reduced at 650 1C for various time.According to Fig. 3, when the reduction time is less than 4 h, thepowder shows mainly a mixture of metallic iron (a-Fe), FeTiO3 andtitania (see Fig. 3(a–d)). It can be seen that the intensity ofdiffraction peak of FeTiO3 deceases gradually, and the diffractionpeak intensity of metallic iron and titania (anatase) phases increasesduring the reduction process. As reduction proceeds under thestrong reducing effect of H2 gas, oxygen removal takes place leadingto the gradual observation of iron formation. Finally, when thepowder is reduced at 650 1C for 4 h, the powder X-ray diffractionpatterns reveal the presence of crystalline a-Fe and titania, and theabsence of any crystalline iron oxides or other crystalline products(see Fig. 3e). According to the observations mentioned above, it isconcluded that the reduction treatment of precursor in flowinghydrogen gas atmosphere causes its formation of iron and titania.

3.4. Mossbauer spectra

Fig. 4 shows the Mossbauer spectra at room temperature forsamples at different stages of reduction treatment (a: 0.5 h, c: 2 h,e: 4 h). The spectra have been fitted with one sextet and twodoublets by computer and shown in Fig. 4. The correspondinghyperfine parameters like effective magnetic field (H), isometricshift (IS), quadrupole splitting (QS), full width at half maximum

(G) and fraction of spectral area (FA) are listed in Table 1. Fig. 4and Table 1 obviously show that the spectra exhibit a sextet withhyperfine parameters that are typical of crystalline a-iron, whichis in agreement with what was reported by others [22]. Theanalysis of the Mossbauer spectra confirms the presence ofmetallic iron in the material prepared using the reduction route.With the reduction time increasing, the intension of the sextetincreases noticeably, and the relative areas of the sextet increasesfrom 15.6% to 92.3% (refer to Table 1), which means the content ofmetallic iron increases accordingly. In addition, the spectra ofsamples exhibit two doublets, indicating the presence of para-magnetic high-spin iron(II) and iron(III). One of the doubletspectra exhibits relative large isometric shift IS (1.03–1.12 mm/s)and quadrupole splitting QS (0.63–0.89 mm/s). The observedhyperfine parameters are similar to FeTiO3 [23], which can beassigned to high-spin iron(II). Another doublet spectra has relativesmall isometric shift of IS (0.21–0.38 mm/s) and quadrupolesplitting QS (0.43–0.75 mm/s), and the isometric shift is lowerthan 0.54 mm/s [24]. The observed hyperfine parameters indicatethat high-spin iron(III) is present. It is difficult to assign the high-spin iron(III) doublet present in the three spectra of Fig. 4 to aspecific compound. With reduction proceeding, the decrease ofdoublet peak intension and the doublet relative areas indicate thatthe content of the high spin iron decreases, which agrees with theresult of X-ray diffraction. By comparing the X-ray diffraction datawith the Mossbauer spectra in this study, we find out the evidentfact that the former could not detect the iron(III)-containing oxidein the prepared composites.

3.5. Magnetic properties

The magnetic characterization of the sample was carried out ina PPMS system at room temperature with a maximum applied

Fig. 4. Room temperature Mossbauer spectra of samples reduced for different

time in a hydrogen atmosphere (a: 0.5 h, c: 2 h, e: 4 h).

Table 1Mossbauer parameters of samples reduced for different time.

Sample Sub-

spectra

IS (mm/s)a QS (mm/s)b G/2 (mm/s)c H (kOe)d FA (%)e

a

Doublet1 0.21 0.43 0.19 9.00

Doublet2 1.06 0.63 0.17 75.4

Sextet1 0.00 0.00 0.15 330.16 15.6

c

Doublet1 0.38 0.68 0.20 3.60

Doublet2 1.12 0.85 0.17 24.30

Sextet1 0.00 0.01 0.14 328.23 72.10

e

Doublet1 0.26 0.75 0.12 1.90

Doublet2 1.03 0.89 0.12 5.80

Sextet1 0.00 0.01 0.13 330.12 92.30

a IS¼Isomer shift.b QS¼Quadrupole splitting.c G¼Full width at half maximum.d H¼Hyperfine magnetic field.e FA¼Fraction of spectral area.

Fig. 5. Static magnetic hysteresis curves of the composites at different reduced

reaction time (a: 0.5 h, c: 2 h, e: 4 h).

X. Tang et al. / Journal of Physics and Chemistry of Solids 73 (2012) 478–483 481

field. Fig. 5 shows M–H hysteresis loops of the specimens at650 1C for 0.5 h, 2 h and 4 h. It is found that the areas of the staticmagnetic hysteresis curves are very small, which illustrates they

are soft magnetic materials. The reduction time has a significanteffect on the specific magnetic saturation as shown in Fig. 5.Specimen reduced for 0.5 h exhibits magnetization of 24.8 emu/g.It is observed that saturation magnetization increases graduallywith the increase of the reduced reaction time as shown in Fig. 5.The increase in the value of saturation magnetization with theincrease in the reduced time is consistent with the grown of a-iron as evidenced from the X-ray and Mossbauer results. Speci-men reduced for 4 h exhibits magnetization of 91.6 emu/g.The value of specific magnetic saturation is lower than theliterature one, 212–220 emu/g (pure mass iron) [25]. The follow-ing three reasons contribute to such a low saturation magnetiza-tion. First, due to the formation of oxidation layers on the ironparticle surface, the surface of the iron particles has magneticdied layer (1–2 nm). Surface environment has been found to beextremely important in determining the magnetic property [26].Second, some iron ions entered the crystal lattice of titania, so itwas difficult to reduce to iron. Third, some metallic iron particleswere inlaid into titania, which behaved as super-paramagneticparticle.

3.6. Microwave absorbing properties

In order to estimate the role of the magnetic and dielectriclosses, we determined to investigate complex permittivity andpermeability of the samples. Complex permittivity (er¼e0 � je00)and complex permeability (mr¼m0 � jm00) represent the dielectricand dynamic magnetic properties of magnetic materials. The realparts of complex permittivity and permeability symbolize thestorage capability of electric and magnetic energies. The imagin-ary parts represent the loss of electric and magnetic energies.The frequency dependence of e0, e00, m0 and m00 for samples a, b, c

and e is shown in Figs. 6 and 7.The variations of complex permittivity (e0, e00) for samples a, b,

c and e over frequency range 2.0–12.0 GHz are shown in Fig. 6.From Fig. 6, we can observe that the real parts (e0) of complexpermittivity show a decreasing trend with the increase of fre-quency. With the reduction time increasing, the imaginary part(e00) of complex permittivity increases, and the values of imagin-ary part of complex permittivity do not show observable changesover this frequency range for all samples. The dielectric propertiesof samples may be mainly due to the variation of compositions.We can know from the above X-ray diffraction study that thecomposite material is composed of metallic iron, FeTiO3 and

Fig. 7. Frequency dependence of the complex permeability for samples a, b, c and

e at a fixed volume fraction (a: 0.5 h, b: 1 h, c: 2 h, e: 4 h).

Fig. 8. Frequency dependence of reflection loss for the sample e at various

thickness.

Fig. 6. Frequency dependence of the complex permittivity for samples a, b, c and e

at a fixed volume fraction (a: 0.5 h, b: 1 h, c: 2 h, e: 4 h).

X. Tang et al. / Journal of Physics and Chemistry of Solids 73 (2012) 478–483482

titania. With the reduction time increasing, the contents of ironand titania increase, which causes the increase of the real part ofpermittivity to a certain extent, the decrease of the content ofFeTiO3 and the separation of the iron by titania. As a result, thereal parts decrease while the electrical resistance increases.The variations of real part (m0) of complex permeability forsamples over frequency range 2.0–12.0 GHz are shown in Fig. 7.As is shown in Fig. 7, the variation tendencies of both the real partand the imaginary part for the samples are similar. With thefrequency increasing, the m0 decreases gradually. Moreover, thevalues of real part also increase with the increase of reductiontime. The imaginary part of complex permeability is interesting inthe magnetic loss. With the reduction time increasing, themaximum values of the imaginary part of complex permeabilityincrease slimly. Moreover, the peak positions of m00 of the samplesshift to a low frequency range. From Figs. 6 and 7, we can observethe e00 and m00 values for all samples are not zero in the mostfrequency range. In addition, each sample has an individualmaterial constant, and therefore each sample shows specificelectromagnetic wave absorption properties.

According to the transmission line theory, the reflection loss ofelectromagnetic radiation, RL (dB), under normal wave incidenceat the surface of a single-layer material backed by a perfectconductor can be defined [20,27]. The microwave absorbingproperties of the powder–resin composites have been calculated

for various measured values of e0, e00, m0 and m00 in Figs. 6 and 7,assuming the layer thickness d¼1.5–4.5 mm. Fig. 8 shows thefrequency dependency of RL for the iron/titanium-oxide compo-sites have different thicknesses. As is shown in Fig. 8, thematching situation can be achieved in a frequency range of 3.8–12 GHz when the thickness is below 4.5 mm. Furthermore, themaximum value less than �30 dB were observed. The reflectionloss maximum is equivalent to the occurrence of minimal reflec-tion of the microwave power for the particular thickness. Withthe increase of thickness of the layer, the matching frequencytends to shift to the lower frequency region. From this relation-ship, we can design an appropriate thickness of electromagneticwave absorber so as to make it suitable for a specific frequency.

4. Conclusion

In this study, we have developed the novel ferromagnetic/dielectric composite particles using the reduction method, inwhich the major phase metallic iron coexists with titanium-oxidephases. Titanium-oxide/iron composites combine the advantagesof dielectric and magnetic absorption materials. It is found that allthe prepared samples exhibit electromagnetic wave absorptionproperties since the e00 and m00 values are not zero in the mostfrequency range. In addition, each sample has an individualmaterial constant, and shows specific electromagnetic waveabsorption properties in different frequency ranges. These com-posites provide us a new material for microwave-absorbingapplication in a frequency range of 2–12 GHz.

Acknowledgments

This work was supported by Science and Technology Innova-tion Foundation for the University students from the School ofPetroleum Engineering. And we express ours thanks to Prof. HuKeao (State Key Laboratory of Metal Matrix Composites, ShanghaiJiao Tong University, China) for his valuable advice and helpduring this investigation.

References

[1] S. Yoshida, M. Sato, E. Sugawara, J. Appl. Phys. 85 (1999) 4636–4638.[2] D. Zabetakis, M. Dinderman, P. Schoen, Adv. Mater. 17 (2005) 734–738.[3] N. Dishovaski, A. Petkov, I. Nedkov, IEEE Trans. Magn. 30 (1994) 969–971.[4] H.T. Kwon, J.Y. Shin, J.H. Oh, J. Appl. Phys. 75 (1994) 6109–6111.

X. Tang et al. / Journal of Physics and Chemistry of Solids 73 (2012) 478–483 483

[5] S. Sugimoto, S. Kondo, K. Okayama, IEEE Trans. Magn. 35 (1999) 3154–3156.[6] M. Pal, S. Bid, S.K. Pradhan, et al., J. Magn. Magn. Mater. 269 (2004) 42–47.[7] J.R. Liu, M. Itoh, et al., J. Appl. Phys. 98 (2005) 0543051–0543057.[8] V. Bovtun, J. Petzelt, V. Porokhonsky, J. Eur. Ceram. Soc. 21 (2001) 1307–1311.[9] M.S. Pinho, M.L. Gregori, A.S. Carvalho, Microwave Opt. Technol. Lett. 32

(2002) 325–327.[10] V.M. Petrov, V.V. Gagulin, Inorg. Mater. 37 (2001) 93–98.[11] H.M. Xiao, W.D. Zhang, S.Y. Fu, Compos. Sci. Technol. 70 (2010) 909–915.[12] A. Verma, A.K. Saxena, D.C. Dube, J. Magn. Magn. Mater. 263 (2003) 228–234.[13] X. Tang, K.A. Hu, Mater. Sci. Eng.: B 139 (2007) 119–123.[14] V.K. Babbar, A. Razdan, R.A. Puri, J. Appl. Phys. 87 (2000) 4362–4366.[15] I. Kong, S.H. Ahmad, M.H. Abdullah, J. Magn. Magn. Mater. 322 (2010)

3401–3409.[16] G.Z. Xie, X.L. Song, B.S. Zhang, Powder Technol. 210 (2011) 220–224.

[17] T. Yamaguchi, S. Taruta, T. Yamakami, K. Kitajima, Mater. Res. Bull. 42 (2007)2143–2149.

[18] S.C. Tjong, Z.Y. Ma, Mater. Sci. Eng. (R) 29 (2000) 49–113.[19] A.R.A. Schettini, R.C.D. Peresb, B.G. Soares, Synth. Met. 159 (2009)

1491–1495.[20] S.S. Kim, S.B. Jo, K.I. Gueon, IEEE Trans. Magn. 27 (1991) 5462–5464.[21] O. Crap, R. Barjega, E. Segal, Thermochim. Acta 318 (1998) 57–62.[22] G.J. Long, D. Hautot, Q.A. Pankhurst, Phys. Rev. B 57 (1998) 10716–10722.[23] D.G. Rethwisch, J.A. Dumesic, J. Phys. Chem. 90 (1986) 1863–1871.[24] Y.P. Ying, Z. Li, Application of Mossbauer Spectra in Mineral Science, Geology

Publishing House, Beijing, 1977 (in Chinese).[25] S. Suzuki, H. Sakumoto, S. Miya, IEEE Trans. Magn. 20 (1984) 39–41.[26] C.R. Vestal, Z.J. Zhang, J. Am. Chem. Soc. 125 (2003) 9828–9833.[27] Y. Natio, K. Suetake, IEEE Trans. Microwave Theory Tech. 19 (1971) 65–72.