低磁场下LaFe_(10.7)Co_(0.9)Si_(1.4)合金磁相变行为的标度理论临界参数研究

Critical Parameters of Scaling Theory for Magnetic Phase Transformation Behavior of LaFe_(10.7)Co_(0.9)Si_(1.4)Alloy under Low Magnetic Field

基于X射线粉末衍射谱,以及等温与等场情况下磁化强度分别随温度与磁场变化的数据,系统地研究了LaFe_(10.7)Co_(0.9)Si_(1.4)合金的磁性以及磁相变类型。M-T曲线中的近似零热滞、居里温度附近Arrott图的直线性、磁熵变随温度变化图的对称状等,均表明LaFe_(10.7)Co_(0.9)Si_(1.4)合金的磁相变为二级相变。基于Arrott图,并结合Arrott-Noakes状态方程和Kouvel-Fisher方程,拟合的相变临界参数分别为β=0.4746与γ=0.9812,β=0.4727和γ=1.0482,二者具有高度的自洽性。另外,根据居里温度附近的等温磁化曲线方法确定了临界指数δ的值,大小为3.1587。这些参数值表明LaFe_(10.7)Co_(0.9)Si_(1.4)合金在相变过程局域磁矩之间的相互作用是长程关联相互作用,属于铁磁-顺磁连续二级相变。另外,通过对不同磁场下合金的磁熵变进行了归一化处理,并结合伦兹函数对归一化曲线进行了拟合,得到了相关拟合系数。

Based on X-ray powder diffraction spectrum,isothermal magnetization and equifield temperature change data,the magnetic properties and magnetic phase transition types of LaFe_(10.7)Co_(0.9)Si_(1.4)alloy were systematically studied in this paper.The approximate zero thermal hysteresis in the M-T curve,the linearity of the arrott diagram near the Curie temperature,and the symmetry of the magnetic entropy change with temperature diagram all show that the magnetic phase transition of LaFe_(10.7)Co_(0.9)Si_(1.4)alloy is a second-order phase transition.Based on Arrott diagram,combined with Arrott-Noakes state equation and Kouvel Fisher equation,the fitted critical parameters of phase transition areβ=0.4746 andγ=0.9812,β=0.4727 andγ=1.0482,the two results have a high degree of self consistency.In addition,the critical index is determined to be 3.1587 by the critical isothermal curve method.These parameter values show that the magnetic interaction of LaFe_(10.7)Co_(0.9)Si_(1.4)alloy can be described by the molecular mean field model based on long-range interaction,that is,the critical interaction of second-order magnetic transformation.In addition,the magnetic entropy change of LaFe_(10.7)Co_(0.9)Si_(1.4)alloy under different magnetic fields was normalized,and the normalized curve was fitted using the Lorentz function to obtain the relevant fitting coefficients.