Phase Separation and Transport Behavior in La0.5Ca0.5-xBaxMnO3

Abstract

We show that for La 0:5 Ca 0:5Àx Ba x MnO 3 , the sample is single phase with an orthorhombic structure for x < x d % 0:28 while a phase separation occurs for x ! x d . The observed phase separation is a chemically driven inhomogeneity caused by the large size-mismatch (s 2 ) which occurs as s 2 ! 1:42 Â 10 À4 nm 2 . In the single-phase region, increasing x to !0:14 causes a transition to metallic state, and the magnetoresistance near the transition shows behavior similar to that in doubleexchange manganite oxides. In the two-phase region, although the compound also shows an insulator-metal transition, both transport and magnetoresistance show behavior completely different from that in the single-phase region. Some anomalous transport and magnetoresistance behaviors are also revealed at low temperatures. A possible phase diagram is presented as a function of T and x and the experimental findings are discussed according to different ground states.

Magnetic properties and low-field magnetoresistance of La0.7Sr0.3Mn0.9M0.1O3 compounds (M=Al, Cr, Mn, Fe, Co, Ni, Cu, and Ga)

“…[72,73]. The Cu ion is generally considered to be a Cu 2+ ion in the compounds [54,56,59,61], and the XPS spectrum shows that the Cu ion is divalent (t 6 2g e 3 g ) in LaMn 1−x Cu x O 3 [55]. For La 0.7 Sr 0.3 Mn 0.9 Cu 0.1 O 3 compound, the spontaneous magnetization is calculated to be 3.10 B /f.u.…”

“…or 3.30 B /f.u., respectively, for AFM or FM coupling between the Cu and Mn magnetic moments, suggesting that the possible coupling is FM. A ferromagnetic coupling between the Cu and Mn magnetic moments is also found from magnetization measurement for La 2/3 Ca 1/3 Mn 0.9 Cu 0.1 O 3 compound [59]. Since the superexchange rules predict a weak AFM Cu 2+ O Mn 3+ superexchange interaction [68], the Cu 2+ O Mn 4+ superexchange interaction should be FM in the Cu-doped compounds.…”

Effect of Ga doping on magneto-transport properties in colossal magnetoresistive La0.7Ca0.3Mn1−xGaxO3 (0<x<0.1)

“…Magnon-polaron and spin-polaron signatures were revealed together with charge localisation mechanisms. Introducing foreign nonmagnetic cations on the Mn site of mixed-valency manganites Ln 1Àx A x MnO 3 is also known to lead to severe modifications of the magnetic and electrical properties, as well in conductive ferromagnetic manganites [8][9][10] as in insulating charge-ordered compounds [11,12]. In the ferromagnetic region due to Mn ions replacement with such metals there are sometimes features ascribed to a weakening of the Zener double-exchange interaction between two unlike ions [13].…”

Effects of silicon addition on the electrical and magnetic properties of copper-doped (La,Ca)MnO3 compounds

“…(i) silica-contaminated La 0.7 Ca 0.3 MnO 3 compounds and (ii) copper-doped La 0.7 Ca 0.3 MnO 3 compounds. As mentioned above, other authors had already studied the copper-doped compounds [26][27][28], but we had to synthesize this series as well since the values of electrical resistivity and transition temperature vary as a function of the synthesis conditions.…”

“…Indeed the first papers on copper doping dealt with La 1-x Ba x Mn 1-y Cu y O 3 [21,22], because of the similarity with the superconductor La 2-x Ba x CuO 4 . Cu doping was also studied in the case of LaMnO 3 [23][24], La 1-x Sr x MnO 3 [25] and more recently La 0.7 Ca 0.3 MnO 3 [26][27][28]. Initially we were interested in copper substitution on the manganese site of La 0.7 Ca 0.3 MnO 3 .…”