Abstract Nanosized La0.7Ca0.3Mn1-xNixO3 (x = 0, 0.02) manganites were synthesized via the auto-combustion method. The critical behavior of these samples was then carefully investigated by analyzing the results of static magnetic measurements near their critical temperatures. The samples exhibited second-order phase transition, and the effect of Ni doping was to lower the critical temperature. The analysis of the experimental data was carried out by means of various techniques, such as modified Arrott plots, the Kouvel-Fisher method, and critical isotherm analysis, which revealed that the values of the critical exponents β, γ, and δ are close to those theoretically predicted by mean-field theory. By using the Widom scaling relation and the universal scaling hypothesis, the dependability of the obtained values of the critical exponents was confirmed. Moreover, the temperature dependence of the spontaneous magnetization was estimated from the analysis of the variation of the magnetic entropy change with the magnetization within the framework of mean-field theory. Interestingly, the spontaneous magnetization determined from the entropy change and that obtained from classical extrapolation of the Arrott curves displayed high concordance. These results strongly suggested that the interactions among spins in the investigated compound are long-range.

中文翻译：

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纳米晶 La0.7Ca0.3Mn1-xNixO3 (x=0, 0.02) 锰酸盐中的铁磁长程有序性

摘要 采用自燃法合成了纳米尺寸的La0.7Ca0.3Mn1-xNixO3 (x = 0, 0.02) 锰酸盐。然后通过分析接近临界温度的静磁测量结果，仔细研究了这些样品的临界行为。样品表现出二阶相变，Ni掺杂的作用是降低临界温度。实验数据的分析采用了各种技术，如修正的阿罗特图、Kouvel-Fisher 方法和临界等温线分析，结果表明临界指数 β、γ 和 δ 的值接近于平均场理论理论预测的那些。通过使用Widom标度关系和通用标度假设，得到的临界指数值的可靠性得到证实。此外，在平均场理论的框架内，通过分析磁熵变随磁化强度的变化来估计自发磁化强度的温度依赖性。有趣的是，由熵变确定的自发磁化强度与从 Arrott 曲线的经典外推法获得的自发磁化强度显示出高度的一致性。这些结果强烈表明所研究化合物中自旋之间的相互作用是长程的。从熵变确定的自发磁化强度与从阿罗特曲线的经典外推法获得的自发磁化强度显示出高度的一致性。这些结果强烈表明所研究化合物中自旋之间的相互作用是长程的。从熵变确定的自发磁化强度与从阿罗特曲线的经典外推法获得的自发磁化强度显示出高度的一致性。这些结果强烈表明所研究化合物中自旋之间的相互作用是长程的。