The Microwave Absorption Properties of La0.67Ba0.33Mn0.98TM0.02O3 (TM=Ti and Ni)

The Microwave Absorption Properties of La

0.67

Ba

0.33

Mn

0.98

TM

0.02

O

3

(TM=Ti and Ni)

Sitti Ahmiatri Saptari

1, a

,

Azwar Manaf

2,b

and Budhy Kurniawan

2,c 1

Faculty of Science and Technology, State Islamic University, Jakarta, Indonesia 2

Departement of Physics, University of Indonesia, Depok, Indonesia

a

siti_ahmiatri@yahoo.co.id, bazwar@ui.ac.id, cbkuru@fisika.ui.ac.id

Keywords: microwave absorption; La0.67Ba0.33Mn0.98Ti0.02O3; La0.67Ba0.03Mn0.98Ni0.02O3

Abstract. The doped lanthanum manganites has unusual magnetic and transport properties, which

makes it possible for this material to be used for absorbing microwave. In this study,

La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni) were prepared by solid state reaction method as

microwave absorption material. The crystal structure and magnetic properties were characterized by XRD and permagraph. Refinement results showed both of samples are single phase with

monoclinic crystal structure. And hysteresis loops results showed that the

La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni) samples are soft magnetic materials. Microwave

absorption properties were investigated in the frequency range 8-12 GHz using vector network analyzer. An optimal reflection loss of -13 dB is reached at 11.5 GHz for TM = Ti and optimal reflection loss of -6 dB is reached at 11.5 GHz for TM = Ni.

.

Introduction

Microwave in the range 1 -20 GHz are increasingly used in the field of wireless communication, local area network, and so on. However, the electromagnetic interference (EMI) limits their applications and hence much attention has been paid to find suitable microwave absorption materials. conventional spinel-type ferrites do not function well in the GHz range due to a drop in

the complex permeability µr as given by Snoek’s limit [1]. In recent years, the doped rare

earth-transition metal oxides, especially doped LaMnO3, with their colossal magneto-resistance (CMR)

effect, have shown high potential applications in the field of magnetic electronics functional materials. Besides the CMR effect, the particular electronic structure and unusual electromagnetic characteristics of the oxide indicate that it has high applications as microwave absorption materials [2-5].

In this paper, with the aim finding a material suitable for use as a microwave absorber in GHz

band range, La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni) powders were prepared by the solid state

reaction method. We investigate the microwave absorption properties of soft magnetic

La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni). Our experimental results demonstrate that

La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni) are promising for the application produce broadband

and effective microwave absorbers.

Experimental

La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) ceramic samples were synthesized following the

solid-state reaction route by mixing La2O3, MnCO3, BaCO3, TiO2 and NiO (Sigma Aldrich 99.99%

purity) in their stoichiometric ratios, with Planetary Ball Milling during 25 hours. Thermogravimetric analyzer (TGA) was used to determine the crystallization temperature. The

calcinations performed at 800oC for 10 h. The calcined powders were then pressed into pellets and

finally sintered at 1200oC for 2 h.

The crystal structure of the samples were determined by X-ray diffraction (XRD) _{using CuKα}

observed by permagraph. The reflection loss (RL) of the samples were measured between 8 and 12 GHz using vector network analyzer.

Result and Discussion

Fig. 1 presents the XRD patterns of the La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples.

The diffraction patterns of all the samples show single phase and free from impurities. Crystal structure was further refined by GSAS software, refinement results of the

La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples can be seen in Table 1. The refinement results

provide information that La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples have formed a single

phase with monoclinic crystal structure and space group I 1 2/c 1.

0 10 20 30 40 50 60 70 80 90

2 theta La_0.67Ba_0.33Mn_0.98Ti_0.02O₃

In

te

n

si

ty

In

te

n

si

ty

La_0.67Ba_0.33Mn_0.98Ni_0.02O₃

Fig. 1. XRD pattern of La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples

Table 1. Refinement results of La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples

Sample a (Å) b(Å) c(Å) β χ2 _{Densitas (g/cm}3₎

Ti 5.53 5.54 7.83 89.95 1.19 6.68

Ni 5.53 5.52 7.82 89.92 1.25 6.72

To study the magnetic properties of the samples, the magnetic hysteresis loops of the samples at room temperature were measured. It is shown that the samples are ferromagnetic behaviors at room temperature. Fig. 2 shows the image of magnetic hysteresis loops, it exhibits the soft

magnetic property of La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples. The values of

saturation magnetization (Ms) are 0.10 T and 0.15 T for La0.67Ba0.33Mn0.98Ti0.02O3 and

-1500 -1000 -500 0 500 1000 1500

-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15

La_0.67Ba_0.33Mn_0.98Ti_0.02O₃

La_0.67Ba_0.33Mn_0.98Ni_0.02O₃

H (kA/m)

J

(T

)

Fig. 2. Hysteresis loops of La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni) samples

7G 8G 9G 10G 11G 12G 13G

-14 -12 -10 -8 -6 -4 -2 0 -7 -6 -5 -4 -3 -2 -1 0

L

o

ss

(d

B)

freq (Hz)

La_0.67Ba_0.33Mn_0.98Ti_0.02O₃

L

o

ss

(d

B)

La_0.67Ba_0.33Mn_0.98Ni_0.02O₃

Reflectivity is usually used as a parameter to characterized the microwave absorption performance. The reflectivity of the single layer absorber could be expressed by the following equation [6] :

Zin = (µ/ɛ)½ tanh (j2πfd(µɛ)½) (1)

Z0 = (µ0/ɛ0)½ (2)

R = 20 log10│( Zin -Z0) / ( Zin + Z0) │ (3)

where Zin and Z0 are the impedances of the absorber and free space respectively, µ and ɛ the

permeability and permittivity of the absorber, µ0 and ɛ0 the permeability and permittivity of free

space, dthe absorber’s thickness.

Fig. 3 shows the reflection loss spectra of the La0.67Ba0.33Mn0.98TM0.02O3 (TM= Ti and Ni)

samples in the frequency range 8 – 12 GHz. It is clear that the position of reflection loss peak

maintain at ~ 11.5 GHz, the maximum values of reflection are -13 dB and -6 dB for

La0.67Ba0.33Mn0.98Ti0.02O3 and La0.67Ba0.33Mn0.98Ni0.02O3 respectively.

Conclusion

In summary, the transition metal doped La0.67Ba0.33Mn0.98TM0.02O3 (TM = Ti and Ni) powders

have been fabricated successfully by the conventional solid state reaction method. Experimental results show that the position of reflection loss peak maintain at ~ 11.5 GHz, the maximum values

of reflection are -13 dB and -6 dB for La0.67Ba0.33Mn0.98Ti0.02O3 and La0.67Ba0.33Mn0.98Ni0.02O3

respectively.

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