Singh Vikram, Bag Pallab, Rawat R, Nath R
School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram, 695551, India.
UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore, 452001, India.
Sci Rep. 2020 Apr 24;10(1):6981. doi: 10.1038/s41598-020-63223-0.
The nature of the magnetic transition, critical scaling of magnetization, and magnetocaloric effect in MnFeSi (x = 0 to 1) are studied in detail. Our measurements show no thermal hysteresis across the magnetic transition for the parent compound which is in contrast with the previous report and corroborate the second order nature of the transition. The magnetic transition could be tuned continuously from 328 K to 212 K with Mn substitution at the Fe site. The Mn substitution leads to a linear increase in the unit cell volume and a slight reduction in the effective moment. A detailed critical analysis of the magnetization data for x = 0.0 and 0.2 is performed in the critical regime using the modified Arrott plots, Kouvel-Fisher plot, universal curve scaling, and scaling analysis of magnetocaloric effect. The magnetization isotherms follow modified Arrott plots with critical exponent (β [Formula: see text] 0.308, γ [Formula: see text] 1.448, and δ [Formula: see text] 5.64) for the parent compound (x = 0.0) and (β [Formula: see text] 0.304, γ [Formula: see text] 1.445, and δ [Formula: see text] 5.64) for x = 0.2. The Kouvel-Fisher and universal scaling plots of the magnetization isotherms further confirm the reliability of our critical analysis and values of the exponents. These values of the critical exponents are found to be same for both the parent and doped samples which do not fall under any of the standard universality classes. The exchange interaction decays as J(r) ~ r following the renormalization group theory and the observed critical exponents correspond to lattice dimensionality d = 2, spin dimensionality n = 1, and the range of interaction σ = 1.41. This value of σ(<2) indicates long-range interaction between magnetic spins. A reasonable magnetocaloric effect ΔS [Formula: see text] -6.67 J/Kg-K and -5.84 J/Kg-K for x = 0.0 and 0.2 compounds, respectively, with a huge relative cooling power (RCP ~ 700 J/Kg) for 9 T magnetic field change is observed. The universal scaling of magnetocaloric effect further mimics the second order character of the magnetic transition. The obtained critical exponents from the critical analysis of magnetocaloric effect agree with the values deduced from the magnetic isotherm analysis.
详细研究了MnFeSi（x = 0至1）中磁转变的性质、磁化强度的临界标度以及磁热效应。我们的测量结果表明，母体化合物在磁转变过程中没有热滞现象，这与之前的报道相反，证实了该转变的二级性质。通过在Fe位点进行Mn替代，磁转变温度可以从328 K连续调节到212 K。Mn替代导致晶胞体积线性增加，有效磁矩略有减小。在临界区域，使用修正的阿罗特图、库维尔 - 费舍尔图、通用曲线标度以及磁热效应的标度分析，对x = 0.0和0.2的磁化数据进行了详细的临界分析。母体化合物（x = 0.0）的磁化等温线遵循修正的阿罗特图，临界指数为（β≈0.308，γ≈1.448，δ≈5.64），x = 0.2时为（β≈0.304，γ≈1.445，δ≈5.64）。磁化等温线的库维尔 - 费舍尔图和通用标度图进一步证实了我们临界分析的可靠性以及指数值。发现母体和掺杂样品的这些临界指数值相同，它们不属于任何标准的普适类。根据重整化群理论，交换相互作用按J(r) ~ r衰减，观察到的临界指数对应于晶格维数d = 2、自旋维数n = 1以及相互作用范围σ = 1.41。这个σ值（<2）表明磁自旋之间存在长程相互作用。对于x = 0.0和0.2的化合物，分别观察到合理的磁热效应ΔS≈ - 6.67 J/Kg - K和 - 5.84 J/Kg - K，在9 T磁场变化下具有巨大的相对冷却功率（RCP≈700 J/Kg）。磁热效应的通用标度进一步模拟了磁转变的二级特征。从磁热效应的临界分析中获得的临界指数与从磁等温线分析中推导的值一致。
