Fe-Ni、Fe-Pt和Fe-Pd铁磁体因瓦效应的数值模拟
Numerical Simulations of the Invar Effect in Fe-Ni, Fe-Pt, and Fe-Pd Ferromagnets
摘要：
本文用一种计算效率高的方法对铁磁Fe-Ni、Fe-Pt和Fe-Pd合金的因瓦效应进行了理论研究。该过程可分为两个阶段：磁性研究和结构性质计算。在第一阶段，考虑了一个伊辛模型，并确定了Fe矩的分数，作为温度的函数。在第二阶段，进行密度泛函理论计算，以评估不同温度下部分无序局部矩态合金的自由能与晶格常数的函数关系。通过对Fe_（1-x）Ni_x（x = 0.35，0.4，.）的热膨胀系数的模拟结果进行比较，对该方案进行了广泛的验证，0.8、Fe 0.72Pt 0.28和Fe 0.68Pd 0.32的测量值。发现该方案在整个供试化合物谱中至少在定性上表现良好。例如，由Guillaume发现的Fe 1-xNix的热膨胀系数在室温附近随着x从0.55减小到0.35而显著减小，这被可靠地再现。由于理论和实验之间的整体定性协议的结果，它出现在Fe-Ni合金的因瓦效应可以在相同的计算框架内的Fe-Pt和Fe-Pd的研究。
英文摘要：
The Invar effect in ferromagnetic Fe-Ni, Fe-Pt, and Fe-Pd alloys is investigated theoretically by means of a computationally efficient scheme. The procedure can be divided into two stages: study of magnetism and calculations of structural properties. In the first stage, an Ising model is considered and fractions of Fe moments which point up as a function of temperature are determined. In the second stage, density-functional theory calculations are performed to evaluate free energies of alloys in partially disordered local moment states as a function of lattice constant for various temperatures. Extensive tests of the scheme are carried out by comparing simulation results for thermal expansion coefficients of Fe1-xNix with x = 0.35, 0.4, ..., 0.8, Fe0.72Pt0.28, and Fe0.68Pd0.32 with measurements. The scheme is found to perform well, at least qualitatively, throughout the whole spectrum of test compounds. For example, the significant reduction of the thermal expansion coefficient of Fe1-xNix as x decreases from 0.55 to 0.35 near room temperature, which was discovered by Guillaume, is reliably reproduced. As a result of the overall qualitative agreement between theory and experiment, it appears that the Invar effect in Fe-Ni alloys can be investigated within the same computational framework as Fe-Pt and Fe-Pd.
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