Anomalous magnetotransport in LaMn1−x Te x O3

Abstract

The LaMn 1−x Te x O 3+δ (x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te 4+ , and Mn 3+ ions are partly converted into Mn 2+ and Mn 4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn 2+ , Mn 3+ and Mn 4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn 3+ is much larger or less than the sum of Mn 2+ and Mn 4+ ; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn 3+ is close to the sum of Mn 2+ and Mn 4+ . These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.colossal magnetoresistance, La-Te-Mn-O, magnetotransport Doped LaMnO 3 have been widely studied due to a rich variety of physical properties [1][2][3][4] . The prominent one is the colossal magnetoresistance (CMR) effect, a phenomenon of the resistive transition induced by the magnetic transition, and CMR is traditionally explained by the double exchange (DE) [5] interaction. The key role in DE mechanism is played by Mn ions, the unique magnetic ions in LaMnO 3 , which affect not only the transport behaviors of manganites by the network of Mn-OMn, but also the magnetism of materials by the spin variation of Mn ions.As demonstrated by numerous studies, the valence of Mn ions in the manganites varies with the dopant, which is considered the intrinsic factor to understanding CMR effect. Mn ions are usually all trivalent (Mn 3+ ) in LaMnO 3 .When La ions were substituted partially by divalent ions, such as Ca 2+ , Sr 2+ etc., some Mn 3+ would convert into Mn 4+ , and Mn 3+ -Mn 4+ mixed valences are formed in the stable manganites of La 1−x A x MnO 3 [5][6][7][8] .When La ions were substituted partially by tetravalent ions, such as Ce 4+ , Te 4+ ... etc., some Mn 3+ would convert into Mn 2+ , which leads to the Mn 2+ -Mn 3+ mixed valence in La 1−x A x MnO 3 (A=Ce 4+ , Te 4+ ...) [8,9] . The interactions between Mn 4+ (or Mn 2+ ) ions and the neighboring Mn 3+ ions via O 2− are believed to contribute to the DE effect.The influence of the La-site substitution in manganites on DE mechanism is indirect, depending on the conversion of Mn 3+ ions. The direct influence, undoubtedly, is the Mn-site substitution. Recently, most studies on the Mn-site substitution focus on the La 1−x A x MnO 3 or LaMnO 3 . It is found that the manganites with the formula of La 1−x A x Mn 1−y O 3 (A=Ca 2+ , Sr 2+ ...; M=Zr 2+ , Cr 3+ , Ta 4+ ,...) or LaMn 1−x B x O 3 (B=T 4+ , Mo 6+ ...) still remain Mn 3+ -Mn 4+ (or Mn 3+ -Mn 2+ ) mixed-valence, and undergo ferro-to para-magnetism (FM-PM) transition. However, both have the different magnetotransport behavior.

Controlling magnetism via transition metal exchange in the series of intermetallics Eu(T1,T2)5In (T = Cu, Ag, Au)

“…Interestingly both, chemical and physical pressure, have a considerable influence on the oxidation state of Eu and, hence, on the magnetic properties of Eucontaining compounds. 5,6 In this context, the far-from-trivial question is how a partial substitution of a few similar non-magnetic elements will affect both the crystal structures and the magnetic ordering of europium within a given structure type, especially, if the oxidation state of Eu remains unaffected. For rare earth systems such as Gd5(SixGe1-x) it is known that the variation of the non-magnetic elements ratio has a tremendous effect on the physical behavior where…”

Design of the Speed Regulating PIG with Butterfly Bypass-Valve

“…Several kinds of bypass mechanism have been developed recently, including the rotary bypass-valve and the linear cut-out valve [6].One is the rotary bypass-valve in bypass mechanism developed by university or pipeline inspection vendor, such as Tuboscope [7] in U.S.A., ROSEN in German, Jiang Shengyuan [8] of BeiHua University and Zhang Shimin [9] of CUPB in China. The other is the linear cut-out valve, also developed by pipeline inspection vendor or university, such as BJ [3] in U.S.A., GE-PII [10] in U.S.A., HUANG Songling [11] of Tsinghua University and Yang Lijian [12] of Shenyang University of Technology in China.…”