Morphological and magnetic characterization of manganites oxide-based nanowires and nanotubes

doi:10.1016/j.physb.2004.09.026

Physica B: Condensed Matter

Volume 354, Issues 1–4, 31 December 2004, Pages 98-103

https://doi.org/10.1016/j.physb.2004.09.026 Get rights and content

Abstract

A morphological and magnetic study of sub-micrometric nanostructures of a manganese oxide-based compound La_0.325Pr_0.300Ca_0.375MnO₃ is presented. Nanowires of 50 and 100 nm and tubes with external diameters of 200 and 800 nm were synthesized. Scanning electron microscopy with EDS microanalysis (SEM) and transmission electron microscopy (TEM) allowed to characterize the morphology and microstructure of these nanostructures. The walls of the nanotubes are composed of on average 40 nm grain size particles, while in nanowires the grains are much smaller, in the range between 4 and 20 nm. In both situations, the small grains present a random crystalline orientation, as it is confirmed by TEM diffraction experiments. Magnetization measurements and hysteresis loops are presented and discussed based on magnetic interaction between the grains, anisotropy considerations and reversal magnetization mechanisms.

Introduction

Research on nanotubes and one-dimensional wires has deserved a considerable effort in the last years. Carbon nanostructures and nanotubes with interesting electric and magnetic properties are at present at the center of attention [1], [2], [3], [4], [5].

The recent discovery and development of a synthesis method for manganite nanotubes opened a wide range of new possible applications [6]. In a recent paper, we reported the synthesis and characterization of 800 nm diameter nanotubes [7]. The walls of the tubes are composed by small nano-grains which are on average 30–40 nm in typical size. The structures become ferromagnetic at low temperatures and the values of the coercivity field could be understood in terms of the anisotropy related to the nanostructures geometry [8].

In this paper, we report the synthesis, micro structural and magnetic characterization of a complete series of La_0.325Pr_0.300Ca_0.375MnO₃ (LPCM) manganite nanotubes and nanowires. Bulk LPCM is a prototypical manganite, exhibiting phase separation effects [9], [10]. Using basically the same synthesis method as in Ref. [7], it was extended to generate hollow tubes of 200 nm diameter and nanowires of 100 and 50 nm diameters, for the same nominal manganite composition.

Section 2 describes the synthesis method and main characterization tools, Section 3 describes the experimental results concerning the structural characteristics and magnetic behavior and Section 4 contains the discussion.

Section snippets

Experimental

Two different ways were used for the preparation of La_0.325Pr_0.300Ca_0.375MnO₃ manganite nanostructures. The templates of porous polycarbonate films were dipped into a solution of stoichiometric cations ratio (set A). Alternatively, the templates were used as filters in an adequate system for syringe filtration (set B). The solution fills the pores in set A by capillarity phenomenon and in set B filling is assisted by a syringe. Porous polycarbonate films were either commercial Isopore™ membrane

Results

Nanotubes are formed using templates with pore size of 1000 and 200 nm while nanowires are prepared from the smallest pore size (100 and 50 nm). Fig. 1 shows a SEM image of one nanotube with 800 nm of diameter (set A). The nanotubes were also studied in the TEM, the results being consistent with the SEM ones. The granular structure of the tube wall is apparent from the figure. The grains are in the range of 20–40 nm. The inset demonstrates the hollow nature on the structures. For both preparation

Discussion

Obtained nanostructures of 200 nm in diameter and above are hollow (nanotubes). Nanostructures of around 100 nm and smaller than this number are formed as wires. Without a complete understanding of this fact, we believe that it should be related to the synthesis mechanism. For the nanotubes, the grains have the same size as for the unconfined powder. Due to the presence of the central hole of the tubes, the grains form in an almost unconfined way. Structures of 100 nm and smaller instead of

Acknowledgments

We acknowledge support from CNEA, Conicet, Fundación Antorchas and ANPCyT PICT 05266.

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Morphological and magnetic characterization of manganites oxide-based nanowires and nanotubes

Abstract

Introduction

Section snippets

Experimental

Results

Discussion

Acknowledgments

Nature (London)

J. Appl. Phys.

Science

Rev. Adv. Mater. Sci.

Appl. Phys. Lett.