Abstract

In this paper, we present a detailed study of the critical behavior around paramagnetic–ferromagnetic phase transition in the nominal composition La_0.65Bi_0.05Sr_0.3Mn_1 – xGa_xO₃ (x = 0 and 0.06). Our powder specimens were synthesized using the conventional solid-state reaction method and analyzed by X-ray diffraction and magnetic measurements. X-ray diffraction analysis at room temperature shows that our specimens La_0.65Bi_0.05Sr_0.3Mn_1 – xGa_xO₃ (x = 0 and 0.06) adopt a rhombohedral structure with R-3C space group. Based on Banerjee criterion, the positive slopes of the Arrott plot confirm the second order magnetic phase transition of our samples. The critical exponent values are calculated by distinct techniques like modified Arrott plot (MAP), Kouvel–Fisher method (KF) and critical isotherm (CI). The determined critical exponents values are close to the 3D-Ising model. Furthermore, the substitution of Mn by Ga leads to the decrease of the critical exponent β and at the same time to the reduction of the Curie temperature T_C. The validity of the determined exponent values is authenticated using the scaling hypothesis, in which the M(T, ε) curves integrate in two universal curves below and above T_C.

中文翻译：

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掺Ga锰的La 0.65 Bi 0.05 Sr 0.3 Mn 1 – x Ga x O 3（x = 0和0.06）的临界行为

摘要

在本文中，我们对标称成分La _0.65 Bi _0.05 Sr _0.3 Mn _{1 –  x} Ga _x O ₃（x = 0和0.06）中顺磁-铁磁相变的临界行为进行了详细研究。我们的粉末样品是使用常规固态反应方法合成的，并通过X射线衍射和磁测量进行了分析。室温X射线衍射分析表明，我们的样品La _0.65 Bi _0.05 Sr _0.3 Mn _{1 –  x} Ga _x O ₃（x= 0和0.06）采用R-3C空间群的菱面体结构。根据Banerjee准则，阿罗特图的正斜率确认了样本的二阶磁相变。临界指数值是通过不同的技术来计算的，例如改进的Arrott图（MAP），Kouvel-Fisher方法（KF）和临界等温线（CI）。所确定的临界指数值接近3D模型。此外，用Ga替代Mn会导致临界指数β降低，同时导致居里温度T _C降低。所确定的指数值的有效性使用定标假设进行验证，其中M（T，ε）曲线集成在T _C之上和之下的两条通用曲线中。