Sains Malaysiana 41(6)(2012): 761–768

Electrical and Magneto-Transport Properties of Magneto-Resistive La_0.7Ca_0.28Sr_0.2Mn_O3

Prepared at Different Sintering Temperature

(Sifat Elektrik dan Magneto-Angkutan La_0.7Ca_0.28Sr_0.2MnO₃ yang disediakan pada

Suhu Sinteran Berlainan)

L.S. Ewe* & R. Ramli

College of Foundation and General Studies, Universiti Tenaga Nasional, Campus Putrajaya

Jalan Ikram-Uniten, 43000 Kajang, Selangor D.E. Malaysia

K.P. Lim

Physics Department, Faculty of Science, Universiti Putra Malaysia, 43400 Serdang, Selangor D.E.

Malaysia

R. Abd-Shukor

School of Applied Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor D.E. Malaysia

Received: 29 September 2011 / Accepted: 16 January 2012

ABSTRACT

The effects of strontium doping on the electrical and magneto-transport properties of magneto resistive La_0.7Ca_0.28Sr_0.02Mn_O3 at different sintering temperatures have been studied. The samples were prepared by the co-precipitation technique (COP) and sintered at 1120, 1220 and 1320 ^oC. XRD patterns revealed that the samples have an orthorhombic structure and the diffraction patterns can be indexed with the Pbnm space group. The insulator metal transition, TIM increased linearly from 261 K to 272 K with the increase in sintering temperature. The magnetoresistance (MR) measurements were made in magnetic fields from 0.1 to 1 T at room temperature. The percentage of MR increased with increasing of magnetic field and sintering temperature for all samples. The electrical resistivity data were fitted with several equations in the metallic (ferromagnetic) and insulator (paramagnetic) regime. The density of states at the Fermi level N(EF) and the activation energy (Ea) of electron hopping were estimated by using variable range hopping and small polaron hopping model.

Keywords: Activation energy; electrical resistivity; magnetotransport; manganites

ABSTRAK

Kesan pengedopan strontium terhadap sifat elektrik dan magneto angkutan bahan magneto rintangan La_0.70Ca_0.28Sr_0.02MnO₃ yang disediakan pada suhu sinteran berlainan telah dikaji. Sampel telah disediakan dengan kaedah co-pemendakan (COP) dan disinter pada 1120, 1220 and 1320 ^oC. Corak XRD menunjukkan semua sampel mempunyai struktur ortorombik dan corak pembelauan boleh diindeks kepada kumpulan ruang Pbnm. Peralihan penebat logam TIM meningkat secara linear daripada 261 hingga 272 K dengan peningkatan suhu sinteran. Pengukuran magneto rintangan (MR) telah dijalankan dalam medan magnet daripada 0.1 hingga 1 T pada suhu bilik. Peratusan peningkatan MR meningkat dengan medan magnet dan suhu sinteran untuk semua sampel. Data kerintangan elektrik telah disuaikan dengan beberapa model dalam rantau logam (feromagnet) dan penebat (paramagnet). Ketumpatan keadaan pada aras Fermi N(EF) dan tenaga pengaktifan (Ea) loncatan elektron telah dijangkakan dengan menggunakan model loncatan julat berubah dan model polaron kecil.

Kata kunci: Kerintangan elektrik; magneto rintangan; manganit; tenaga pengaktifan

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*Corresponding author; email: laysheng@uniten.edu.my