Elsevier

Journal of Alloys and Compounds

Volume 700, 5 April 2017, Pages 169-174
Journal of Alloys and Compounds

Structural and magnetotransport properties of the Si doped B-site in La0.6Gd0.1Sr0.3 Mn1-xSixO3 (0 ≤ x ≤ 0.15) manganite

https://doi.org/10.1016/j.jallcom.2016.12.277Get rights and content

Highlights

  • La0.6Gd0.1Sr0.3Mn1-xSix O3 (0x0.15) compounds were prepared using sol-gel technique.

  • The manganite phase crystallizes in a rhombohedra (R-3c) structure.

  • The samples exhibit a second order FM-PM phase transition at TC.

Abstract

The influence of partial substitution of Mn by Si on the structural, magnetic and electrical properties of La0.6Gd0.1Sr0.3Mn1-xSixO3 (0 ≤ x ≤ 0.15) is studied. All compositions were synthesized using the sol-gel technique. X-ray diffraction and structure refinement show that they crystallize in the rhombohedra structure with the R3¯c space group. The magnetization and electrical measurements versus temperature proved that all samples exhibit a paramagnetic to a ferromagnetic transition and a semi-conductor to a metallic one when the temperature decreases. The substitution of Mn by silicon (Si) leads to a continuous decrease of both the Curie temperature TC (from 350 K for x = 0.0–278 K for x = 0.15) and the resistivity transition temperature TM-Sc (from 325 K for x = 0.0–263 K for x = 0.15). The magnetoresistance (MR) as well as the resistivity are found to increase.

Introduction

The perovskite manganites Tr3+1-xM2+xMnO3 (where, e.g.Tr = Nd, Pr, La, Sm,Y and M = Ba, Sr, Ca, Pb) have been a popular subject of contemporary research because of their interesting physical properties such as competing metal-semiconductor transitions, magnetic orders and high (colossal) magnetoresistance(CMR) and also have potential applications in spintronic, for magnetic reading heads, memories recording and magnetic sensors [1], [2], [3], [4], [5]. The parent compound, TrMnO3 is a charge-transfer (CT) insulator with trivalent manganese in different layers coupled among themselves antiferromagnetically through a superexchange mechanism. When the Tr site is doped with a divalent ion, a proportional number of Mn3+ ions are converted into Mn4+ ions and mobile eg electrons are introduced; which has lead to mediating the ferromagnetic interaction according to double exchange between Mn3+ and Mn4+ with electronic configuration (3d4,t2g3eg1,S=2) and (3d3,t2g3eg0,S=3/2) respectively. The magnetic properties of Tr1-xMxMnO3 phases are strongly affected by the Mnsingle bondO bond length and Mnsingle bondOsingle bondMn bond angle controlled by the ionic radii of A and B site ions and Mn3+/Mn4+ ratio which modifies the double exchange and superexchange interactions [6]. The relation between magnetic and transport properties of CMR materials is explained by competing antiferromagnetic superexchange between Mn3+-Mn3+/Mn4+-Mn4+ and ferromagnetic double exchange between Mn3+-Mn4+ which are accompanied by the Jahn- Teller effect. In order to understand the unusual structure, magnetic and magnetocaloric effect (MCE) properties of doped perovskites Tr1-xMxMnO3, many studies have been carried out by doping the trivalent rare earth site (A-site) with divalent atoms (Ca, Sr, Ba, etc) [7], [8], [9]. Also, other studies have shown that substitution of Mn (B-site) dramatically affects the structure, magnetic and magnetocaloric effect properties [10], [11]. The B-site modification has merit in that it directly affects the Mn network by changing the Mn3+/Mn4+ ratio and the electron carrier density. Therefore, several investigations were carried out in order to understand the correlation between the structure, magnetic, electrical and MR (%) of Tr1-xMxMnO3 by doping with elements such as Cr, Ni, V, Ga, Co, Mg and Al at B-site [12], [13], [14], [15]. However, doping of silicon at B-site in Tr1-xMxMnO3 is not investigated so far. Therefore, in order to better understand the role of Mn and its local environment in La0.6Gd0.1Sr0.3MnO3, we studied the effects of replacing some of the Mn with Si. The choice of the ion Si4+ is based on the ionic radius (0.4 Å) is smaller than that of the Mn4+ (0.53 Å). In view of this, the authors have taken up the present work with an objective to study the effect of silicate at Mn-site on the structural, magnetic and magnetotransport properties of La0.6Gd0.1Sr0.3Mn1-xSixO3 (0 ≤ x ≤ 0.15) compounds. These compounds were investigated by X-ray diffraction, magnetization and electrical measurements and the results are presented here. The second objective of this work is to find a new compound, exhibiting a large MR value, which is highly preferred for practical applications.

Section snippets

Experimental method

The microstructure of ceramic materials in general and CMR manganite materials in particular are highly affected by the preparation routes and heat treatments. The synthesis procedures based on the conventional ceramic or solid-state reaction methods are not suitable for advanced and technological applications, as these methods produce particles of large size, faulty homogeneity and often-secondary phases. Alternatively, sol-gel routes are recognized methods to produce high quality homogenous

Crystal structure

XRD patterns of the illustrated samples in Fig. 1 present sharp and intense peaks corresponding to the perovskite phase. An enlarged scale of the most intense peak (104) Bragg reflections shows a shift to higher 2θ values indicating that the lattice parameters decrease with increasing Si content. The structure refinement was performed in the hexagonal setting of the rhombohedral R3¯c(Z = 6) space group (No 167), in with the atomic positions are (La, Gd, Sr): 6a (0, 0, 0.25), (Mn, Si): 6b(0, 0,

Conclusions

To summarize, we have studied the structure, magnetic, electrical and magnetoresistance properties of La0.6Gd0.1Sr0.3Mn1-xSixO3 (x = 0.00, 0.05, 0.10 and 0.15) nanocrystalline manganites prepared using the sol-gel technique. All samples crystallize in a rhombohedra structure (R-3c space group). The doping decreases the cell volume and modifies the grain size of the samples. It also decreases both the Curie and metal-semiconductor transition temperatures. Electrical properties of all compounds

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