Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites

doi:10.1016/j.physleta.2016.06.056

Physics Letters A

Volume 380, Issue 38, 7 September 2016, Pages 3107-3110

https://doi.org/10.1016/j.physleta.2016.06.056 Get rights and content

Highlights

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Chemical pressure through doping enhances ferromagnetism in the same way as the application of a magnetic field.
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The enhancement of the FM phase fraction on cooling is preceded by a strong lattice contraction.
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The magnetic properties are linked to structural changes in phase separated manganites.

Abstract

We investigate a series of manganese oxides, the La_0.225Pr_0.4( ${Ca}_{1 - x} {Sr}_{x}$ )_0.375MnO₃ system. The $x = 0$ sample is a prototype compound for the study of phase separation in manganites, where ferromagnetic and charge ordered antiferromagnetic phases coexist. Replacing Ca²⁺ by Sr²⁺ gradually turns the system into a homogeneous ferromagnet. Our results show that the material structure plays a major role in the observed magnetic properties. On cooling, at temperatures below $\sim 100 K$ , a strong contraction of the lattice is followed by an increase in the magnetization. This is observed both through thermal expansion and magnetostriction measurements, providing distinct evidence of magneto-elastic coupling in these phase separated compounds.

Introduction

The study of manganese based perovskites, known as manganites, has fascinated the scientific community for the last two decades. This interest was triggered by the discovery of the colossal magnetoresistance effect [1], a huge reduction of the electrical resistivity on application of a magnetic field, which was explained in terms of the interplay between the double exchange mechanism and quenched disorder [2]. In addition, the competition between very different phases with similar ground state energies, namely an insulating charge ordered antiferromagnetic (CO-AFM) and a metallic ferromagnetic (FM) state, leads to complex phase diagrams [3], and to the occurrence of a phase separated state [4], [5], where both phases can spontaneously coexist in meso- or nanoscopic scales [6], [7], [8]. Phase separation (PS) in manganites has became a very important topic of investigation in the physics of strongly correlated electron systems, and a similar phenomenology is found in the high Tc cuprates [9], particularly in the underdoped regime, as well as in magnetocaloric materials, such as Gd₅Ge₄ [10].

A prototype compound to investigate the phenomenon of phase separation in manganites is ${La}_{5 / 8 - y} \Pr_{y} {Ca}_{3 / 8} {MnO}_{3}$ , which has been thoroughly studied in the literature [11], [12], [13], [14]. It is a mixture of the optimized colossal magnetoresistive compound La_0.625Ca_0.375MnO₃, with the Pr based system, Pr_0.625Ca_0.375MnO₃, known to have a robust CO-AFM state at low temperatures. The intermediate mixture, La_0.225Pr_0.40Ca_0.375MnO₃, becomes charge ordered and highly insulating below 230 K, and orders antiferromagnetically below 180 K. Phase separation manifests itself at lower temperatures, below $\approx 80 K$ , where FM metallic clusters which nucleate within the CO-AFM matrix yield a sizable magnetization even in low applied magnetic fields.

In this work we performed additional doping to the above mentioned phase separated compound, La_0.225Pr_0.40Ca_0.375MnO₃, by replacing the alkaline-earth Ca²⁺ with larger Sr²⁺ ions. This substitution introduce structural distortions that gradually increases the exchange coupling [15], thus promoting the FM phase at low temperatures, eventually leading to a homogeneous FM ground state. Our objective is to correlate the macroscopic magnetic response of the system with its structural behavior, obtained from thermal expansion and magnetostriction measurements. The results clearly show that the formation of FM clusters on cooling occurs at temperatures just below a strong lattice contraction of the material, giving evidence of the coupling between structural and magnetic degrees of freedom in phase separated manganites.

Section snippets

Experimental

Polycrystalline samples of La_0.225Pr_0.4( ${Ca}_{1 - x} {Sr}_{x}$ )_0.375MnO₃, with $0 \leq x \leq 1$ , were synthesized by a citrate–nitrate decomposition method [16], using 99.9% purity reactants (oxides and soluble salts). After the mixed solution was dried at 100 °C, thermal treatments were made at 500 °C for 5 hours and at 1400 °C for 16 hours. The powder was compacted into pellets of $5 \times 2 \times 2 {mm}^{3}$ using a pressure 8 t/cm². The pellets were finally sintered at 1400 °C for 2 hours. The resulting average grain size is ∼2 μm.

Results and discussion

Fig. 1 shows the room temperature x-ray diffraction intensity of La_0.225Pr_0.4( ${Ca}_{1 - x} {Sr}_{x}$ )_0.375MnO₃, with $x = 0.05$ . Rietveld refinements were carried out with the FULLPROF program, with an orthorhombic Pnma space group. The reliability factors of the Rietveld analysis [18] are $R_{Bragg} = 9.04$ , $R_{F} = 9.81$ , and $χ^{2} = 1.57$ . The inset shows an enlarged plot of specific areas of the diffractogram, so that the calculated and observed profiles are clearly visible. The lower trace in the main panel is a plot of the

Conclusions

To summarize, our results demonstrate that magneto-structural coupling plays a major role in the balance between competing phases in phase separated manganites. Chemical pressure through doping and the application of an external magnetic field have a similar effect, enhancing the FM phase fraction of the compound. Sr doping in the La_0.225Pr_0.4( ${Ca}_{1 - x} {Sr}_{x}$ )_0.375MnO₃ system increases the cell volume, and at the same time reduces the distortion of the Mn–O–Mn bond angle, which favors the FM double

Acknowledgements

This research was supported by the bilateral cooperation FAPERJ-CONICET, the Brazilian agencies CNPq and CAPES (Science without borders program), and by the Brazilian Synchrotron Light Laboratory (LNLS). We acknowledge the useful help of Fabiano Yokaichiya and Helio Salim Amorim with the analysis of the x-ray data. LFC acknowledges the UK EPSRC.

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Critical behavior investigated through magnetocaloric effect in PrSrMnO and Pr(Sr,Ca)MnO manganites
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In this work we investigate the critical behavior of two manganite compounds, Pr_0.5Sr_0.5MnO₃ (PSMO) and Pr_0.5Sr_0.41Ca_0.09MnO₃ (PSCMO). These are complex magnetic systems, which undergo a paramagnetic to ferromagnetic phase transition on cooling, followed by a first order magnetic transition to a charge ordered antiferromagnetic states at lower temperatures. Magnetization measurements and magnetocaloric calculations were performed in order to determine their critical behavior. As a main result we show that the scaling of the entropy change $- Δ S_{M}$ with magnetization $M$ , instead of the usual scaling with magnetic field $H$ , is a powerful tool to study the critical behavior through magnetocaloric analysis. We use this property, in conjunction with Modified Arrot Plot technique, to determine the basic critical exponents $β$ and $γ$ for each sample. The exponents values indicate that the samples are near to universality class models based in nearest neighbor interactions. Besides intrinsic differences between the Ca-doped and the undoped sample, we confirm the applicability of the magnetocaloric analysis in order to determine critical behavior in complex magnetic systems.
Critical behavior at high magnetic fields in LaPr(Ca,Sr)MnO manganites
2021, Physica B: Condensed Matter
In this work, we demonstrate that La_0.225Pr_0.4(Ca_1−xSr_x)_0.375MnO₃ manganites with $0 \leq x \leq 0.10$ , exhibit a discontinuous first order ferromagnetic-paramagnetic transition at temperatures ~ 230–240 K, which evolves to a continuous second order ferromagnetic-paramagnetic transition according to the intensity of the applied magnetic field. Under high magnetic fields and through a magnetization scaling analysis, we have determined the critical exponents of the sample with x = 0.05 - β = 0.15, γ = 0.77, and δ = 6.24, and x = 0.10 - β = 0.165, γ = 0.62, and δ = 4.69. The exponents values obey the scaling laws but do not belong to any existing universality class. This analysis of critical behavior can be used to predict the magnetic entropy change under high magnetic fields.
Thermal cycling effects on static and dynamic properties of a phase separated manganite
2018, Journal of Magnetism and Magnetic Materials
Citation Excerpt :
This lack of low temperature relaxation after thermal cycling shows that the sample is able to reconfigure its low temperature state, getting closer to equilibrium state after each cycle is performed. This is accompanied by a reconfiguration on its structural and magnetic properties, as it was shown, for instance, by magnetostriction measurements [30]. This scenario is compatible with an accumulative accommodation strain occurring each time the low temperature state is reached.
In this work we address the interplay between two phenomena which are signatures of the out-of-equilibrium state in phase separated manganites: irreversibility against thermal cycling and aging/rejuvenation process. The sample investigated is La_0.5Ca_0.5MnO₃, a prototypical manganite exhibiting phase separation. Two regimes for isothermal relaxation were observed according to the temperature range: for T > 100 K, aging/rejuvenation effects are observed, while for T < 100 K an irreversible aging was found. Our results show that thermal cycles act as a tool to unveil the dynamical behavior of the phase separated state in manganites, revealing the close interplay between static and dynamic properties of phase separated manganites.
Thermal cycling effects on static and dynamic properties of a phase separated manganite
2018, arXiv

View full text

Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

Phys. Rep.

Mater. Chem. Phys.

Thousandfold change in resistivity in magnetoresistive La–Ca–Mn–O Films

Science

Complexity in strongly correlated electronic systems

Science

Mesoscopic and microscopic phase segregation in manganese perovskites

Phys. Rev. B

Remarkable magnetic relaxation and metamagnetic transition in phase-separated La0.7Ca0.3Mn0.9Cu0.1O3 perovskite

J. Appl. Phys.

Magnetic imaging of a supercooling glass transition in a weakly disordered ferromagnet

Nature Materials

Inhomogeneous magnetism in La-doped CaMnO3. II. Nanometric-scale spin clusters and long-range spin canting

Phys. Rev. B

Research progress on electronic phase separation in low-dimensional perovskite manganite nanostructures

Nanoscale Res. Lett.

Recent developments in the theoretical study of phase separation in manganites and underdoped cuprates

J. Phys.: Cond. Matter

Correlating the local magnetic properties of the magnetic phase transition in Gd5Ge4 using scanning Hall probe imaging

Phys. Rev. B

Remarkable magnetic relaxation and metamagnetic transition in phase-separated La_0.7Ca_0.3Mn_0.9Cu_0.1O₃ perovskite

Inhomogeneous magnetism in La-doped CaMnO₃. II. Nanometric-scale spin clusters and long-range spin canting

Correlating the local magnetic properties of the magnetic phase transition in Gd₅Ge₄ using scanning Hall probe imaging