关键字：Colossal magnetoresistance;Ceramic materials - Doping (additives) - Grain boundaries - Lanthanum compounds - Manganese compounds - Manganites - Niobium - Niobium oxide - Rare earths - Strontium compounds - Tunnelling magnetoresistance;Calcined temperature - High field magnetoresistance - Low-field magnetoresistance - Magnetic and electrical properties - Noncollinear spin structures - Rare-earth manganite - Spin dependent transport - Spin dependent tunneling
摘要：The magnetic and electrical properties of La<inf>0.67</inf>Sr<inf>0.33</inf>MnO<inf>3</inf>( LSMO ) are influenced very much by the Nb dopant. However, this doping effect is restricted by the limited Nb solution into LSMO due to the low calcined temperature. As a result, a second phase LaNbO<inf>4</inf>appears in our samples. Enhancements of the low-field magnetoresistance (LFMR) were observed both at 77 K and room temperature in the manganite system prepared by doping Nb<inf>2</inf>O<inf>5</inf>into LSMO powders. The doping amount x of Nb ions ranges from 0-10 % molar ratio. The MR ratios at 77 K with H = 1 T and H = 0.1 T are 33.8 % and 24 % for the x = 0.07 doped sample, respectively. A MR effect up to 9 % was also found for the sample with x = 0.05 at room temperature, which is 2.2 times as large as that for LSMO (4.1%). The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the LFMR while the high field magnetoresistance (HFMR) originates from the spin dependent transport related to noncollinear spin structure at the interfaces. © (2011) Trans Tech Publications.<br/>
卷号：675 677
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