Faculty of Physics, University of Białystok, Białystok, Poland.
J Phys Condens Matter. 2010 Jul 28;22(29):296005. doi: 10.1088/0953-8984/22/29/296005. Epub 2010 Jun 29.
Determination of the Mössbauer absorption cross section, σ(E), and accurate reconstruction of the hyperfine field distributions of the invar alloy, Fe(64)Ni(36), by the maximum entropy method (MEM) is presented. The procedure consists of three steps: deconvolution of the Mössbauer spectra with the instrumental resolution function using MEM, nonlinear transformation of the deconvoluted spectrum into σ(E), and reconstruction of the hyperfine field distribution. In order to test the procedure of the deconvolution and correction for thickness effect, several simulated spectra with thickness parameter 1 < t < 50 and different values of Lorentzian FWHM of the source and absorber were analyzed. It is shown that the procedure of the deconvolution and extraction of σ(E) works well for spectra whose lines contain at least five experimental points per FWHM. Reconstructed distributions of hyperfine field parameters, based on the extracted Mössbauer cross section of the Fe-Ni invar alloy, measured with and without application of an external magnetic field, are discussed. The reconstruction has been made to test the earlier postulated non-collinear ferromagnetic state of invar without referring to any specific model in the analysis of the Mössbauer results. It is shown that marginal probability distribution of hyperfine magnetic field consists of the main maximum at about 28 T and a broad tail extending down to 5 T. Observed isomer shift of the main maximum is small and positive. The isomer shift decreases with magnetic field and attains negative values at the lowest fields. It is shown that the magnetic texture parameter does not depend on the hyperfine magnetic field. One thus concludes that in the invar Ni-Fe alloys, in contrast to some theoretical predictions, there is no evidence for different arrangements of the iron magnetic moments as a function of the magnetic hyperfine field.
采用最大熵法（MEM）测定了因瓦合金 Fe(64)Ni(36)的穆斯堡尔吸收截面σ(E)，并对其超精细场分布进行了精确重建。该方法包括三个步骤：使用 MEM 对穆斯堡尔谱进行仪器分辨率函数的反卷积、将反卷积谱非线性变换为 σ(E)，以及重建超精细场分布。为了检验反卷积和厚度效应修正的程序，分析了几种具有厚度参数 1<t<50 和源和吸收体的洛伦兹线宽 FWHM 不同的模拟谱。结果表明，对于每条线至少包含五个实验点的 FWHM 的谱，该反卷积和 σ(E)提取程序效果良好。讨论了基于提取的 Fe-Ni 因瓦合金穆斯堡尔截面，在施加和不施加外磁场的情况下测量的超精细场参数的重建分布。这种重建是为了检验早期提出的因瓦非共线铁磁态，而无需在分析穆斯堡尔结果时参考任何特定模型。结果表明，超精细磁场的边缘概率分布由约 28 T 的主极大值和延伸到 5 T 的宽尾巴组成。观察到的主极大值的同晶位移很小且为正。同晶位移随磁场而减小，并在最低磁场下达到负值。结果表明，磁织构参数与超精细磁场无关。因此得出结论，与一些理论预测相反，在因瓦 Ni-Fe 合金中，没有证据表明铁磁矩的排列随磁超精细场而变化。
