Critical Behavior of Ti Doping La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} Perovskite System
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DOI: 10.1007/s10948-012-1485-5
Abstract
Polycrystalline La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} (x=0 and 0.05) samples are prepared by solid-state methods, and all of them have a hexagonal perovskite structure, revealed by X-ray diffraction. The critical properties at the ferromagnetic–paramagnetic transition have been analyzed from data of static magnetization measurements for the samples. The value of critical exponents, derived from the magnetic data using the Kouvel–Fisher method, yield 0.345≤β≤0.386, 1.194≤γ≤1.306, and 4.383≤δ≤4.466 with a T _{ C } of 321.36–350.48 K. The exponent values are close to those expected for three-dimensional (3D) Heisenberg ferromagnets with is short-range magnetic interaction.
Keywords
Critical phenomena Perovskite Magnetic properties1 Introduction
Over the past few years, the manganites with the form of Ln_{1−x }A_{ x }MnO_{3} (Ln = trivalent rare earth, A = divalent alkaline earth) have attracted much attention due to their extraordinary magnetic and electronic properties and their promise for the future technological applications [1–3]. A prominent feature of these materials is a insulator–metal transition together with a paramagnetic (PM)–ferromagnetic (FM) transition and a colossal magnetoresistance (CMR) effect, which has been extensively explained in the framework involving a double-exchange model and Jahn–Teller effects [4, 5]. Earlier studies on the critical behaviors around the Curie temperature T _{ C } have indicated that critical exponents play important roles in elucidating interaction mechanisms near T _{ C } [6]. Critical phenomena in the double exchange (DE) model have been first described within mean-field theory [7]. However, the theoretical calculations based on simplified DE models, reveal that the FM–PM transition in CMR manganites should belong to the Heisenberg universality class [8]. By contrast, the experimental estimates for critical exponents are still controversial including those for short-range Heisenberg interaction [9, 10], the mean-field values [11], and those which cannot be classified into any universality class ever known [12]. Hence, the critical properties of the paramagnetic–ferromagnetic phase transition in manganites pose an important fundamental problem. The aim of this work was to study the effect of Ti-doping La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} (x=0 and x=0.05) polycrystalline samples on the structural, magnetic, and the critical parameter.
2 Experimental
In this study, La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} (LNPMT) compounds were formed by the standard solid state reaction by mixing 99.994% pure PbCO_{3}, TiO_{2}, MnO_{2}, La_{2}O_{3}, and Nd_{2}O_{3} powders. The detailed experimental process has been reported elsewhere [13]. The physical properties of every stage were measured. The magnetization properties and the XRD pattern were measured and compared with previous reports to ensure the formation of the same compounds. The structure and phase purity of the prepared samples were checked by X-ray diffraction (XRD), using CuKα _{1} radiation at room temperature. The magnetization measurements were carried out by the superconducting interference device (SQUID). For the studies, the isothermal M vs. H is corrected by a standard procedure from low field dc magnetization measurements. In fact, the internal field used for the scaling analysis has been corrected for demagnetization, H=H _{appl}−D _{ a } M, where D _{ a } is the demagnetization factor obtained from M vs. H measurements in the low-field linear-response regime at a low temperature.
3 Scaling Analysis
4 Results and Discussion
Crystallographic data for La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} (x=0 and x=0.05) from the Rietveld refinement of X-ray diffraction data
x |
0 |
0.05 |
---|---|---|
a (Å) |
5.4899(4) |
5.5015(4) |
c (Å) |
13.3558(3) |
13.3723(3) |
V (Å^{3}) |
349.10(4) |
351.03(1) |
d _{(Mn,Ti)–O} (Å) |
1.960 (2) |
1.963 (4) |
θ _{(Mn,Ti)–O–(Mn,Ti)} (°) |
165.8 (5) |
165.2 (3) |
Discrepancy factors | ||
R _{wp} (%) |
13.2 |
9.60 |
R _{ p } (%) |
7.63 |
9.55 |
R _{ F } (%) |
2.24 |
3.15 |
χ ^{2} (%) |
3.87 |
3.66 |
Transition temperature T _{ C }, θ _{ p }, \(\mu_{\mathrm{eff}}^{\mathrm{th}}\), and \(\mu_{\mathrm{eff}}^{\exp}\) as a function of x content for La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3}
Composition |
T _{ C } (K) |
θ _{ p } (K) |
\(\mu_{\mathrm{eff}}^{\mathrm{th}}\) (μ _{B}) |
\(\mu_{\mathrm{eff}}^{\mathrm{exp}}\) (μ _{B}) |
---|---|---|---|---|
La_{0.57}Nd_{0.1}Pb0_{.33}MnO_{3} |
350 |
351.15 |
4.72 |
5.36 |
La_{0.57} Nd_{0.1}Pb0_{.33}Mn_{0.95}Ti_{0.05}O_{3} |
322 |
321.22 |
4.64 |
4.33 |
Values of the β, γ, and δ as determined from the modified Arrott plots, Kouvel–Fisher plot and the critical isotherm are given for La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{1−x }Ti_{ x }O_{3} (x=0 and x=0.05). The theoretically predicted values of exponents for various universality classes are given for the sake of comparison
Composition |
Ref. |
T _{ C } (K) |
β |
γ |
δ | ||||
---|---|---|---|---|---|---|---|---|---|
Technique |
Technique |
Technique |
Technique | ||||||
MAP^{a} |
KF^{b} |
MAP^{a} |
KF^{b} |
MAP^{a} |
KF^{b} |
Critical isotherm (experimental) |
Critical isotherm (calculated) | ||
La_{0.57}Nd_{0.1}Pb_{0.33}MnO_{3} |
This work |
350.18 |
349.48 |
0.371 |
0.386 |
1.380 |
1.306 |
4.270 |
4.383 |
La_{0.57}Nd_{0.1}Pb_{0.33}Mn_{0.95}Ti_{0.05}O_{3} |
This work |
321.24 |
321.36 |
0.391 |
0.345 |
1.276 |
1.194 |
4.470 |
4.466 |
Mean field model |
[21] |
– |
0.5 |
1 |
3 | ||||
3D-Heisenberg model |
[21] |
– |
0.365 |
1.336 |
4.80 | ||||
3D-Ising model |
[21] |
– |
0.325 |
1.241 |
4.82 |
Concerning the value of δ, it can be determined directly from the critical isotherm M (T _{ C },H).
5 Conclusion
In summary, we have investigated the effect of Ti doping in La_{0.57}Nd_{0.1}Pb0_{.33}MnO_{3} on the structural, magnetic, and critical parameters. The lattice parameters, unit cell volume, the (Mn/Ti)–O–(Mn/Ti) bond angle, and the (Mn/Ti)–O bond length increase with increasing Ti content. The Curie temperature T _{ C } is reduced by Ti doping level. The critical parameters β, γ, and δ estimated from various techniques match reasonably well. The values of the critical exponents are very close to the values for the 3D-Heisenberg ferromagnet with short-range interactions.
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