Giant magnetoresistance in bulk La 0.6 Mg 0.4 MnO 3
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Giant magnetoresistance in bulk La0.6 Mg0.4 MnO3 Yadong Li,a) X. F. Duan, J. H. Zhang, H. R. Wang, and Y. T. Qian Department of Applied Chemistry, University of Science & Technology of China, Hefei, Anhui 230026, People’s Republic of China
Z. Huang, J. Zhou, and S. L. Yuan High Magnetic Laboratory, Institute of Plasma Physics, Academia Sinica, Hefei, Anhui 230031, People’s Republic of China
W. Liu and C. F. Zhu Laboratory of Internal Friction and Defects in Solids, Academia Sinica, USTC, Hefei, Anhui 230026, People’s Republic of China (Received 24 September 1996; accepted 26 March 1997)
A bulk sample of La0.6 Mg0.4 MnO3 has been prepared from coprecipitated carbonate precursor for the first time in this study. Structure analysis conducted by powder x-ray diffraction indicates that the sample ° ¢ is in the cubic perovskite phase. It shows a metal-insulator transition at 115 K Tp . When applied to an external field, GMR effects are observed in the whole measured temperature range. The maximum negative MR value reaches as large as 480% at 105 K and 5 T. There may be two different mechanisms governing the GMR effects in the sample for the temperatures below and above Tp .
I. INTRODUCTION
Materials exhibiting giant magnetoresistance (GMR) undergo an extremely large change in electrical resistance in response to an applied external magnetic field. This effect is of scientific relevance to interpret the mechanism governing the electrical and magnetic properties of such kind of materials, and of technological interest because of its potential application in magnetic recording and switching devices. GMR effects were first found in metallic multilayers in 1988.1 Only very recently has it been observed in metal oxide.2 The MR (%) value [defined as 100(R(0) 2 R(H))/R(H)] is especially large in hole-doped manganese oxide with a perovskite structure (typified by Ln12x Bx MnO3 ). For example, it reaches 127,000% in LaCaMnO films at 77 K and 6 T.3 The magnetic and electrical properties of holedoped manganese oxides were extensively studied in the early 1950s.4–8 The end composition of La12x Bx MnO3 sx 0d, LaMnO3 is an antiferromagnetic insulator. However, by properly hole-doping with a divalent element B in LaMnO3 , it can show a metal-insulator transition around Curie temperature TC . Below TC it is metal-like and ferromagnetic, ° but¢ above TC it is insulator-like, resulting in a peak Tp around TC in the R-T curve. The mechanism of such a transition is intriguing. Partial substitution of La31 by B21 in the parent compound LaMnO3 can bring about a mixed valence of Mn element. It is believed that the electrical and magnetic properties of the materials are strongly a)
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J. Mater. Res., Vol. 12, No. 10, Oct 1997
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connected to the mixed valence of the Mn element. 3 1 The Mn31 ion has an electron configuration of t2g eg 3 0 and Mn41 t2g eg . The t2g electrons are localized
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