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Author Halim, S.A. ♦ Koh, S.F. ♦ Chow, S.P. ♦ Saion, E.B. ♦ Mansor, H. ♦ Daud, W.Y.W.
Source IEEE Xplore Digital Library
Content type Text
Publisher Institute of Electrical and Electronics Engineers, Inc. (IEEE)
File Format PDF
Copyright Year ©1998
Language English
Subject Domain (in DDC) Natural sciences & mathematics ♦ Physics ♦ Electricity & electronics ♦ Technology ♦ Engineering & allied operations ♦ Applied physics
Subject Keyword Semiconductivity ♦ Magnetic properties ♦ Conductivity ♦ Temperature ♦ Electric resistance ♦ Electric variables measurement ♦ Ceramics ♦ Measurement standards ♦ Probes ♦ Magnetic semiconductors
Abstract Electrical resistivity measurements of La/sub 0.67/Ca/sub 0.33/Mn/sub 1-x/Dy/sub x/O/sub 3/, x=0 to 0.12, ceramics have been studied using a standard four point probe technique, while the magnetic behaviour has been studied using AC susceptibility techniques. The transport properties show the transition from semiconducting to metallic conductivity at T/sub p/ and paramagnetic-ferromagnetic transitions, T/sub c/, were observed in the /spl chi/-temperature curves for all samples. The existence of metallic conductivity, T/sub p/, and ferromagnetism, T/sub c/, were found to be linearly correlated. This phenomenon of coexistence is due to the double exchange interaction of two electrons in Mn/sup 3+/-O/sup 2-/-Mn/sup 4+/ and Mn/sup 4+/-O/sup 2-/-Mn/sup 3+/ configuration which brings the system below T/sub c/ into a metallic state. Hence, it is observed that the Curie temperature T/sub c/ is closely related to the sharp decrease in electrical resistivity of the samples. However, both transition temperatures shift to lower temperatures as dysprosium doping increases, indicating the loss of ferromagnetic order and transport properties. As for the transport properties, the semiconductor model ln(/spl sigma/)/spl sim/(E/sub g//2kT) was used to explain the conduction mechanism of perovskite manganites above T/sub p/. It was concluded that the total conductivity /spl sigma//sub tot/ consists of the intrinsic and extrinsic components such that /spl sigma//sub tot/=/spl sigma//sub int/+/spl sigma//sub ext/. The energy gap decreases initially from 0.11 eV to a minimum value of 0.06 eV at x=0.03 and increases again to 0.08 eV at the composition of x=0.12 for the extrinsic region.
Description Author affiliation: Dept. of Phys., Putra Malaysia Univ., Serdang, Malaysia (Halim, S.A.)
ISBN 0780349717
Educational Role Student ♦ Teacher
Age Range above 22 year
Educational Use Research ♦ Reading
Education Level UG and PG
Learning Resource Type Article
Publisher Date 1998-11-24
Publisher Place Malaysia
Rights Holder Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Size (in Bytes) 307.41 kB
Page Count 5
Starting Page 194
Ending Page 198

Source: IEEE Xplore Digital Library