Elsevier

Journal of Alloys and Compounds

Volume 584, 25 January 2014, Pages 617-624
Journal of Alloys and Compounds

The influence of disorder on critical behavior near the paramagnetic to ferromagnetic phase transition temperature in (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 doped manganite

https://doi.org/10.1016/j.jallcom.2013.09.025Get rights and content

Highlights

  • The critical behavior is sensitive to the disorder.

  • The critical exponents not fit with any model for J4 and J5 samples.

  • The scaling plots show that the critical exponents are reliable.

  • The Griffiths phase and metamagnetic behavior lead to novel critical exponents.

Abstract

The (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 have been elaborated by the solid-state method and checked by X-ray diffraction. Close to magnetic temperature transition, the order transition and the critical behavior are investigated by dc magnetization measurements versus x and y compositions. Using various techniques such as modified Arrott plots, Kouvel–Fisher method, and Widom scaling relation, the values of TC ferromagnetic transition temperature, as well as the β, γ and δ critical exponents are estimated. The scaling plots show that the obtained values of the critical exponents are reliable. As main results, metamagnetic behavior and Griffiths phase were observed in these compounds pointing out to unconventional critical exponent.

Introduction

During few previous years, the perovskite manganites with ABO3-type compounds R1−xAxMnO3, where R stands for the trivalent rare-earth element such as La, Pr, Nd, Sm and A for the divalent alkaline earth ion such as Sr, Ca, Ba, and Pb, have attracted much attention due to their extraordinary magnetic and electronic properties as well as their promise for the potential technological applications [1], [2], [3]. Moreover, for these compounds, electronic, magnetic and structural orders are competed leading to very rich phase diagrams. Also, number of recent studies focused on the investigation of phenomena such as colossal magnetoresistance and charge ordering state [4], [5]. The double exchange theory and the Jahn–Teller effect were used to understand the ferromagnetic–paramagnetic (FMPM) phase transition associated with an insulator–metal (IM) transition in the manganites [6], [7], [8].

However, the observation of Griffiths phase (GP) [9] in materials presenting notably complex magnetic interactions has lately attracted significant scientific interest. In addition, numerous of the recent studies related to GP in manganites concern the R/A-site disorder. Indeed, it has been suggested that disorder may be one of the reasons behind the scattering in experimental results. Existing results suggest that the phase transition in systems with quenched disorder should be qualitatively different from that in pure systems. The critical properties of manganites with the Griffiths phase were studied in many works [10], [11]. Furthermore, more recent investigations have brought forward the ferromagnetic phase transition in these materials type [12], [13], [14]. Understanding this issue, it is necessary to investigate the critical behavior at the phase transition temperature with further details. To shed light on the relation between insulator–metal transition and CMR effect, two important questions about PMFM transition should be clarified: one concerns the order of the phase transition; the second is related to the universality class.

The study of critical behavior of PM to FM transition in RE1−xAExMnO3 manganites provides important information about the nature of magnetic interaction and its influence on the electrical transport properties.

Here, we present a detailed study of the critical behavior and its evolution with quenched disorder σ2 in (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 polycristalline samples with constant fraction Mn3+/Mn4+ and constant average ionic radius of the A-site 〈rA〉 but with different variance σ2 values ranging from 0.5287 10−3 to 4.3247 10−3 Å2. We report the variation of critical exponents for the samples with second order phase transition [J3 (σC2=1.335×10-3 Å2); J4 (σ2 = 1.4481 × 10−3 Å2); J5 (σ2 = 4.3247 × 10−3 Å2)].

Section snippets

Experimental details

A series of samples (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 [(J1 (x = 0, y = 0); J2 (x = 0.05, y = 0.04) J3 (x = 0.25, y = 0.20); J4 (x = 0.3, y = 0.24); J5 (x = 0.98, y = 0.8)] with the same A-site cational mean radius 〈rA = 1.2038 Å and the same average valence of the Mn ion (3.33) but with different A site ionic radii variance σ2 were chosen for the present study. The detailed preparation procedure and basic physical properties are found in Ref. [15]. as previously reported in Ref. [15], the inverse of the magnetic

Scaling analysis

As known, critical exponents are not defined for the first-order transition probably due to the transition shift induced by the applied magnetic field, leading to a field-dependent phase boundary TC(H) [17]. Based on the scaling hypothesis, a second-order phase transition near to the Curie point TC is characterized by a set of interrelated critical exponents, β (associated with the spontaneous magnetization), γ (relevant to the initial magnetic susceptibility), δ (associated with the critical

Results

It is clear that the nature of the magnetic transition in the manganite is still controversial. As underlined in numerous studies. Phan et al. [20] reported first-order magnetic transition (FOMT) in La0.7Ca0.3MnO3 manganite. This observation is also confirmed by Lin et al. [21] when they explain the failure of critical scaling in La0.7Ca0.3MnO3 owing to a transition which is not an ordinary second-order ferromagnetic transition. According to the investigation based on neutron diffraction

Discussion

From this analysis, we can see that the scaling is well obeyed. Indeed, all the data fall on two universal curves, one for temperatures below TC and the other for temperatures above TC. This confirms that the obtained values of the critical exponents and Curie temperature are reliable and in agreement with the scaling hypothesis suggesting that the values TC, β, γ and δ are reasonably accurate. Scaling analysis is well obeyed for J3 (σC2=1.335×10-3 Å2) and J4 (σ2 = 1.4481 × 10−3 Å2) samples while a

Conclusion

Study the effect of quenched disorder σ2 on the critical behavior in (La1−xNdx)2/3(Ca1−ySry)1/3MnO3 polycrystalline sample at the PM-FM phase transition is reported. This transition is identified to be second order for J3 (σC2=1.335×10-3 Å2); J4 (σ2 = 1.4481 × 10−3 Å2) and J5 (σ2 = 4.3247 × 10−3 Å2) compounds. Reliable critical exponents δ, γ, and β were estimated from various techniques such as modified Arrott plot, Kouvel–Fisher method and critical isotherm analysis. For J3 (σC2=1.335×10-3 Å2) sample,

Acknowledgments

This work is supported by the Tunisian National Ministry of Higher Education, Scientific Research and the French Ministry of Higher Education and Research of CMCU 10G1117 collaboration, within the frame work of collaboration Franco–Tunisian.

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