Elsevier

Materials Letters

Volume 63, Issues 24–25, 15 October 2009, Pages 2167-2170
Materials Letters

Magnetic and electrical behaviour of La0.67Ba0.33Mn1 − xFexO3 perovskites

https://doi.org/10.1016/j.matlet.2009.07.019Get rights and content

Abstract

(La0.67Ba0.33)Mn1 − xFexO3 manganites compounds have been prepared by doping up to 20% of Fe at the Mn site. As previously reported in the literature paramagnetic (PM) to ferromagnetic (FM) phase transition has been observed in materials with low Fe doping (≤ 10%). In our x = 0 and x = 0.05 compounds the Curie temperature (TC) is close to room temperature. Above 10% Fe amount, specimens exhibit a glass magnetic behaviour with a spin- or cluster-like freezing process that can be related to a loss of ferromagnetic double exchange interaction. Below 10% of Fe3+ doping electrical-resistivity measurement shows metal – semiconductor transition with a maximum peak of resistivity (ρmax) at a temperature TP close to TC. Above 10% of Fe3+ doping amount the materials exhibit only semiconductor behaviour. Both TC and TP decrease with doping rates with an increasing difference in temperature (TP being lower than TC). Results are consistent with a reduction of the number of available hopping sites for the Mn eg(↑) electron due to substitution of Mn3+ by Fe3+ that suppress the double exchange (DE) interactions.

Introduction

Perovskite manganese oxides R1 − xAxMnO3 (R — trivalent rare earth, A — bivalent ion) are materials with very interesting electrical and magnetic properties, and potential applications for magnetic recording and magnetic sensors [1], [2], [3], [4] have been considered owing to their colossal magnetoresistance (CMR). In order to explain such properties, the double exchange (DE) model was initially proposed [5], [6], [7]. However, a recent study [8] has pointed out that DE alone cannot explain the CMR behaviour and a strong Jahn–Teller effect has been considered. CMR properties can be tuned toward chemical substitution. In particular several authors report on Mn substitution by transition elements [9], [10], [11], [12], [13], [14], [15]. Along this line the doping of Fe at Mn site has been study over a wide range of composition in La1 − xSrxMnO3 [16], [17], [18], [19], La1 − xCaxMnO3 [20], [21], [22], [23]. Only a reduced range of composition has been explored in La0.67Ba0.33Mn1 − xFexO3 manganites corresponding to a low percentage doping of Fe (0 ≤ x ≤ 0.1) [9]. In order to investigate magnetic and electrical properties on this system over a larger composition range, and especially to determine the limiting value of Fe doping which eliminates the metal – semiconductor (MS) transition, we have studied the substitution up to 20% of Fe substitution (0 ≤ x ≤ 0.2). Fe appears as an interesting choice of dopant element because the ionic radii of Mn3+ and Fe3+ are close to each other [24], and thus it is expected that the crystalline structure will not be modified by this substitution. As a consequence lattice effects on electrical and magnetic properties may be ignored and effects due to the variation in the electronic configuration of the different ions become accessible. Fe may therefore be used as a control parameter to vary the magnetic and transport properties of these manganites.

Section snippets

Experimental

Perovskite manganese oxides La0.67Ba0.33Mn1 − xFexO3 (0 ≤ x ≤ 0.2) were prepared by solid state reaction at 1180 °C. The microstructure was observed by scanning electron microscope (SEM). Powder X-ray diffraction (XRD) patterns were carried out with a “PANalytical X'Pert Pro” diffractometer with filtered (Fe-filter) Co radiation. The structure refinement was carried out by the Rietveld analysis of the powder XRD data with the FULLPROF software [25]. The temperature dependence of the magnetization in

Structural properties

Fig. 1 exemplifies the XRD patterns for x = 0 and x = 0.15 compounds. All La0.67Ba0.33Mn1 − xFexO3 samples show single phase with rhombohedral R3̄c symmetry. The position of the most intense peak (lower inset of Fig. 1) has a negligible shift with varying Fe composition, indicating that the cell volume of La0.67Ba0.33Mn1 − xFexO3 specimens should be not affected by Fe doping. The average crystallites sizes, determined by Rietveld refinement, are estimated to be between 40 and 50 nm and hence no

Conclusion

We have prepared La0.67Ba0.33Mn1 − xFexO3 (0 ≤ x ≤ 0.2) manganese oxides by ceramic method at 1180 °C. XRD structure analysis and SEM morphological investigation have been shown that the relatively high Fe3+ doping-level doesn't affect both structure parameters and grain sizes of these manganites due to similar ionic radius of Mn3+ and Fe3+. Magnetization investigations both with temperature M(T), and with magnetic field M(H), show a paramagnetic (PM) to ferromagnetic (FM) phase transition at TC and

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