MnO3 Nanowires Research Articles

Weakening of charge order and antiferromagnetic to ferromagnetic switch over in Pr0.5Ca0.5MnO3 nanowires

We have prepared crystalline nanowires (diameter ∼50nm, length ∼a few microns) of the charge-ordering manganite Pr0.5Ca0.5MnO3 using a low reaction temperature hydrothermal method and characterized them using x-ray diffraction, transmission electron microscopy, superconducting quantum interference device (SQUID) magnetometry and electron magnetic resonance measurements. While the bulk sample shows a charge ordering transition at 245 K and an antiferromagnetic transition at 175 K, SQUID magnetometry and electron magnetic resonance experiments reveal that in the nanowires phase, a ferromagnetic transition occurs at ∼105K. Further, the antiferromagnetic transition disappears and the charge ordering transition is suppressed. This result is particularly significant since the charge order in Pr0.5Ca0.5MnO3 is known to be very robust, magnetic fields as high as 27 T being needed to melt it.

Microstructure and magnetic properties of orderedLa0.62Pb0.38MnO3 nanowire arrays

Highly ordered La0.62Pb0.38MnO3 nanowire arrays are successfully fabricated using an improved sol–gel templatemethod. The x-ray diffraction and transmission electron microcopy results revealthat the nanowires are polycrystalline with uniform diameter around 50 nm.Magnetic measurement indicates that the ferromagnetic transition temperatureTC of the nanowires is around 308 K, which is lower than that of the correspondingbulk material. The nanowire arrays demonstrate the perpendicular magneticanisotropy as a result of shape anisotropy and enhanced coercivity compared with bulkmaterials and the temperature dependence of the saturation magnetization exhibits aT1.25 behaviour. The growth mechanism of the nanowires is also briefly discussed.

Magnetoresistive La0.67Sr0.33MnO3 Nanowires

Magnetoresistive La0.67Sr0.33MnO3 nanowires (NWs) have been synthesized using pulsed-laser deposition, with a template of MgO NWs. Transport studies reveal a remarkable metal–insulator transition at 325 K, accompanied by room-temperature colossal magnetoresistance (MR) of ∼ 10 % under a 1 T magnetic field. Shape-induced MR was observed for magnetic fields applied parallel or perpendicular to the NW (see Figure).

Transition Metal Oxide Core−Shell Nanowires: Generic Synthesis and Transport Studies

A generic non-equilibrium synthesis technique has been developed to produce novel transition metal oxide nanowires, including YBa2Cu3O6.66, La0.67Ca0.33MnO3, PbZr0.58Ti0.42O3, and Fe3O4. Key to our success is the growth of vertically aligned single-crystalline MgO nanowires, which worked as excellent templates for epitaxial deposition of the desired transition metal oxides and led to high-quality core−shell nanowires. Transport studies on La0.67Ca0.33MnO3 nanowires have revealed the remarkable persistence of metal−insulator transition and magnetoresistance down to nanometer scale. Our technique will enable various in-depth studies such as phase transition in nanoscale oxides and may pave the way for novel applications of these fascinating materials.

Hydrothermal synthesis of single-crystalline La0.5Ca0.5MnO3 nanowires at low temperature

Single-crystalline La0.5Ca0.5MnO3 nanowires have been successfully prepared by a hydrothermal method at low temperature. X-Ray diffraction (XRD) results show that the La0.5Ca0.5MnO3 nanowires have an orthorhombic perovskite structure without any other impurity phase. Transmission electron microscopy (TEM) images demonstrate that the as-synthesized samples are made up of a large quantity of nanowires with lengths ranging from several to several tens of micrometers and uniform diameter (∼80 nm). High-resolution transmission electron microscopy (HRTEM) images reveal that the nanowires with very clean surfaces grow along [100]. The result of magnetic measurements indicates that the nanowires have an enhanced Tc due to the shrinkage of the unit cell volume.

Hydrothermal synthesis of La0.5Ba0.5MnO3 nanowires

La 0.5 Ba 0.5 MnO 3 nanowires were synthesized by a hydrothermal method at low reaction temperature (270 °C). The synthesized nanowires are of pure, cubic perovskite structure and single crystalline. They grow along [110]; their surfaces are clean, very regular, and without any sheathed amorphous phase. Typical lengths of the nanowires are in the range of several to several tens of micrometers, and typical widths are in the range of 30–150 nm. Nanowires may be an ideal system for studying dimensionally confined transport phenomena in perovskite manganites and for fabricating field sensors and other devices.