Structural and magnetic properties of the colossal magnetoresistance perovskiteLa 0.85 Ca 0.15 Physical review. B, Condensed matter (2000)
Maxim V. LobanovА. М. БалагуровVladimir PomjakushinPeter FischerM. GutmannArtem M. AbakumovO.G. D’yachenkoEvgeny V. AntipovO. I. LebedevGustaaf Van Tendeloo
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Abstract:
A single phase sample of ${\mathrm{La}}_{0.85}{\mathrm{Ca}}_{0.15}{\mathrm{MnO}}_{3}$ with uniform cation distribution and complete oxygen stoichiometry was synthesized by freeze-drying technique and studied by a variety of methods. The sample is ferromagnetic below ${T}_{C}=170\mathrm{K}$ with ${\ensuremath{\mu}}_{\mathrm{Mn}}=2.9(1){\ensuremath{\mu}}_{B}$ at 10 K. Precise examination of the crystal structure by a combination of electron diffraction, high-resolution electron microscopy, and neutron powder diffraction revealed a monoclinic distortion of the ${\mathrm{GdFeO}}_{3}\ensuremath{-}$type structure $[\mathrm{S}.\mathrm{G}.{P2}_{1}/c,$ $a=7.74476(6)\AA{},$ $b=5.50398(4)\AA{},$ $c=5.47351(4)\AA{},$ $\ensuremath{\beta}{=90.091(2)}^{0}]$ with nonequivalent ${\mathrm{MnO}}_{2}$ layers alternating along the a axis. The crystal structure is characterized by a specific pattern of Mn-O distances implying an unconventional orbital ordering type. A possible relation to charge ordering is described within the bond valence sum framework.Keywords:
Monoclinic crystal system
Colossal Magnetoresistance
Charge ordering
Colossal Magnetoresistance
Manganite
Charge ordering
Metal–insulator transition
Ionic radius
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Abstract Charge ordering (C.O.) in the colossal magnetoresistive (CMR) manganites gives rise to an insulating, high-resistance state. This charge ordered state can be melted into a low-resistance metallic-like state by the application of magnetic field. Thus, the potential to attain high values of magnetoresistance with the application of small magnetic fields may be aided by a better understanding of the charge-ordering phenomenon. This study focused on microstructural characterization in Nd1/2Sr1/2MnO3. In Nd1/2Sr1/2MnO3, the nominal valence of Mn is 3.5+. On cooling, charge can localize and lead to a charge ordering between Mn 3+ and Mn 4+. The ordering of charge results in a superlattice structure and a reduction in symmetry. Thin foil specimens were prepared from bulk samples by conventional thinning and ion milling (at LN2 temperature) methods. The TEM work was carried out in a Philips CM30 at 300 kV with a Gatan LN2 cold stage, and a JEM 4000EX with a resolution of 0.17 nm at 400 kV for HREM observation.
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Colossal Magnetoresistance Manganite Perovskites: Relations between Crystal Chemistry and Properties
Manganites with the perovskite structure represent a very important family of oxides which are extensively studied for their colossal magnetoresistance (CMR) properties. In the present review we discuss the different factors which govern the magnetic and transport properties of these materials: carrier concentration, average size of the interpolated cation, and mismatch effect on the A-site. Three types of oxides are mainly examined: (i) the hole doped manganites Ln0.7A0.3MnO3 (A = Ca, Sr, Ba), (ii) the "charge ordered" Ln0.5A0.5MnO3 manganites, and (iii) the electron doped manganites Ca1-xLnxMnO3 and Ca1-xThxMnO3. The relationships between structural and magnetic transitions are discussed, and particular attention is paid to charge ordering phenomena. The doping of the Mn sites by various elements (Al, Ga, In, Ti, Sn, Fe, Cr, Co, Ni) is systematically examined. The beneficial effect of "Cr, Co, Ni" elements, which induce CMR properties in these perovskites, is emphasized.
Colossal Magnetoresistance
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Colossal Magnetoresistance
Charge ordering
Manganite
Jahn–Teller effect
Atmospheric temperature range
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Oxygen isotope effects observed in the metallic and the charge ordered phase of colossal magnetoresistance manganites are investigated by employing the combined theoretical model of the double exchange and interacting lattice polaron mechanism. We have shown that the isotope effects on the magnetic transition temperature T/sub C/ in the metallic phase and the charge ordering transition temperature T/sub CO/ in the charge ordered phase of manganites can be explained well in terms of the present model with reasonable physical parameters.
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The structure and charge ordering (CO) behavior of the three-dimensional colossal magnetoresistive manganite Nd0.5Sr0.5MnO3 have been studied by transmission electron microscopy. The electron diffraction analysis suggested its room temperature structure as orthorhombic, with a Pnma space group. By controlling the experimental temperature setting either above or below the CO transition temperature, it was observed that the CO grew through the propagation of the CO front. The twin boundaries were the barriers of the CO front movement. In heavily ion irradiated samples, it was observed that the CO front was pinned by the intracrystalline defects, forming a zigzag shape interface. Moreover, the electron beam was observed to influence the CO.
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Charge ordering
Colossal Magnetoresistance
Orthorhombic crystal system
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Lanthanum manganite
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Charge ordering
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Thin films of Nd0.5Ca0.5MnO3 manganites with colossal magnetoresistance (CMR) properties have been synthesized by the pulsed-laser deposition technique on (100)-(SrTiO3). The lattice parameters of these manganites and correlatively their CMR properties can be controlled by the substrate temperature TS. The maximum CMR effect at 50 K, calculated as the ratio ρ(H=0T)/ρ(H=7T) is 1011 for a deposition temperature of TS=680 °C. Structural studies show that the Nd0.5Ca0.5MnO3 film is single phase, [010]-oriented and has a pseudocubic symmetry of the perovskite subcell with a=3.77 Å at room temperature. We suggest that correlation between lattice parameters, CMR, and substrate temperature TS result mainly from substrate-induced strains which can weaken the charge-ordered state at low temperature.
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Pulsed Laser Deposition
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The CMR manganites Ln1 − xAxMnO3 with the perovskite structure form a very important family of magnetic oxides, studied for their fascinating colossal magnetotransport properties. In this review, we discuss two phenomena, charge ordering and phase separation, which are crucial for the appearance of CMR in these oxides. We propose a new route to CMR, based on the Mn-site doping of these materials by other cations, such as Cr, Co, Ni and Ru.
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