Sains Malaysiana 38(5)(2009): 673–678

Magnetic, Electrical Transport and Impedance Spectroscopy Studies

on Ti Substituted La0.67Sr0.33MnO3 Ceramics

(Kajian Sifat Magnet, Angkutan Elektrik dan Spektroskopi Impedans Terhadap Seramik La_0.67Sr_0.33MnO₃ Diganti Ti)

Z. Zalita*

School of Applied Physics

Faculty of Science and Technology, Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor D.E., Malaysia

S.A. Halim, K. P. Lim, Z.A. Talib, Z. Hishamuddin & C.P. Walter

Department of Physics, Faculty of Science

Universiti Putra Malaysia 43400 UPM Serdang, Selangor, Malaysia

Received: 15 September 2008 / Accepted: 16 December 2008

ABSTRACT

La0.67Sr0.33Mn1-xTixO3 samples with x = 0.0, 0.2, 0.4 and 0.6 have been prepared using the conventional solid-state reaction method. The structure, magnetic and electrical transport properties as well as the impedance spectroscopy of the samples were investigated. The powder XRD analysis showed that all samples were single phase with rhombohedral perovskite structure. The magnetization curve suggests that the Ti substituted samples exhibit weak ferromagnetic behaviour. The highest magnetoresistance (MR) value was obtained for sample x = 0.2 at temperature 200 K and field 1 T, which was 32.5%. Low field magnetoresistance (LFMR) effect was observed for the x = 0.0 sample. The metal-like resistivity curve for the x = 0.0 sample was best fitted with ρ = ρo + ρ2T2 equation, indicating the grain boundary effects and electron-electron scattering process contribution. Semiconductor-like transport behaviour was observed for the Ti substituted samples and can be fitted by variable range hopping (VRH) and small polaron hopping (SPH) mechanisms. The activation energy of the samples increased when the Ti composition increased. An equivalent circuit was proposed for the impedance plot with a series of two parallel RC circuits. The grain, grain boundary and electrode resistance values increased with Ti composition due to the reduction of the Mn3+ / Mn4+ ratio.

Keywords: Electrical transport; impedance spectroscopy; magnetoresistance

ABSTRAK

Sampel La0.67Sr0.33Mn1-xTixO3 dengan x = 0.0, 0.2, 0.4 dan 0.6 telah disediakan menggunakan kaedah tindak balas keadaan pepejal yang konvensional. Struktur, sifat magnet dan elektrik serta spektroskopi impedans bagi kesemua sampel telah dikaji. Analisis corak XRD serbuk menunjukkan bahawa kesemua sampel adalah sefasa dengan struktur perovskit rombohedral. Lengkung pemagnetan mencadangkan bahawa sampel dengan penggantian Ti menunjukkan kelakuan feromagnetik yang lemah. Nilai magnetorintangan (MR) yang maksimum diperolehi bagi sampel dengan x = 0.2 pada suhu 200 K dan medan 1 T iaitu 32.5%. Magnetorintangan medan rendah (LFMR) diperolehi bagi sampel x = 0.0. Lengkung kerintangan seperti logam bagi sampel x = 0.0 paling baik dipadankan dengan persamaan ρ = ρo + ρ2T2 yang menunjukkan sumbangan kesan sempadan butiran dan proses penyerakan elektron-elektron. Kelakuan angkutan seperti semikonduktor telah diperhatikan untuk sampel-sampel yang diganti Ti dan dapat dipadankan dengan mekanisma loncatan julat bolehubah (VRH) dan loncatan polaron kecil (SPH). Tenaga pengaktifan sampel meningkat dengan kandungan Ti. Litar setara telah dicadangkan bagi plot impedans dengan siri dua litar RC yang selari. Nilai-nilai rintangan butiran, sempadan butiran dan elektrod meningkat dengan kandungan Ti disebabkan oleh pengurangan nisbah Mn3+ / Mn4+.

Kata kunci: Angkutan elektrik; magnetorintangan; spektroskopi impedans

REFERENCES

Ang, R., Sun, Y.P., Zhu, X.B. & Song, W.H. 2006. Influence of Te doping on the perovskite manganite La0.5Ca0.5MnO3. Solid State Commun. 138: 505-510.

Blasco, J., Garcia, J., Teresa, J.M., Ibarra, M.R., Algarabel P.A. & Marquina, C. 1996. A systematic study of structural, magnetic and electrical properties of (La1-xTbx)2/3Ca1/3MnO3 perovskites. J. Phys.: Condens. Matter 8: 7427-7422.

Behera, B., Nayak, P. & Choudhary, R.N.P. 2007. Impedance spectroscopy studies of NaBa2V5O15 ceramic. J. Alloys and Compound 436: 226-232.

Brahma, S., Choudhary, R.N.P. & Thakur, A.K. 2005. AC impedance analysis of LaLiMo2O8 electroceramics. Physica B 355: 188-201.

Dagotto, E., Hotta, T. & Moreo, A. 2001. Colossal magnetoresistant materials: The key role of phase separation. Phys. Rep. 344: 1-153.

Elliott, S.R. 1983. Physics of Amorphous Materials. London: Longman, 2912.

Hwang, H.Y., Cheong, S.W, Ong, N.P. & Batlogg, B. 1996. Spin polarized intergrain tunneling in La2/3Sr1/3MnO3. Phys. Rev. Lett. 77: 2041-2044.

Jha, P., Rai, S., Ramanujachary, K.V., Lovland, S.E. & Ganguli, A.K. 2004. (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3: A new titano-manganate with a high dielectric constant and antiferromagnetic interactions. Solid State Chem. 177: 2881-2888.

Kallel, N., Frohlich, K., Pignard, S., Oumezzine, M. & Vincent, H. 2005. Structure, magnetic and magnetoresistive properties of La0.7Sr0.3Mn1-xSnxO3. J. Alloys and Compound 399: 20-26.

Li, X.H., Huang, Y.H., Yan, C.H., Wang Z.M. & Liao, C.S. 2002. Enhanced low field magnetoresistance in Mn substituted nanocrystalline La0.7Sr0.3Mn0.9M0.1O3. J. Phys.: Condens. Matter 14: L177-l183.

Millis, A.J., Littlewood, P.B. & Shraiman, B.I. 1995. Double exchange alone does not explain the resistivity of La1-xSrxMnO3. Phys. Rev. Lett. 74: 5144-5147.

Mott, N.F. & Davis, E.A. 1971. Electronic Processes in Noncrystalline Materials. Oxford: Clarendon.

Venkataiah, G., Krishna, D.C., Mital, M., Rao, S.S., Bhat, S.V., Prasad, V., Subramanyam, S.V. & Reddy, P.V. 2005. Effect of sintering temperature on electrical transport properties of La0.67Ca0.33MnO3. Physica B 357: 370-379.

Zener, C. 1951. Interaction between d-shells in the transition metals. ii ferromagnetic compounds of manganese with perovskite structure. Phys. Rev. 82: 403-405.

*Corresponding author; email: zalizai69@gmail.com