Temperature‐dependent local atomic structures in the traditional Fe₆₅Ni₃₅ Invar alloy by X‐ray fluorescence holography

Abstract

Fe and Ni Kα X‐ray fluorescence holography measurements were conducted on a single crystal Fe65Ni35 Invar alloy at 100 and 300 K to investigate the temperature dependence of the 3‐dimensional local structures around the Fe and Ni atoms, respectively. Local structural information was obtained by detailed analyses using a L1‐regularized linear regression for the experimental data. At 100 K, the local atomic arrangements around both the elements show fcc structures. At 300 K, however, only the image around Fe shows a bcc‐like neighboring arrangement. From these X‐ray fluorescence holography data, we propose a model that with increasing temperature, an Fe atom with the low‐spin state enters at the central position of the fcc lattice and is stabilized. And then, large angular positional fluctuations are induced for the atoms at the face‐centered positions around the central Fe atom only.

Applications of a L1‐Regularized Linear Regression to X‐Ray Fluorescence Holography Data of Functional Materials

“…The XFH experiments on the functional materials introduced in this article were performed in collaboration with the coauthors of Hosokawa et al, Stellhorn et al, and Ideguchi et al The authors thank Professor Ichiro Akai and Professor Masato Okada for useful information on the sparse modeling. The XFH experiments were performed at BL6C of PF‐KEK (Nos.…”

“…In this article, we present the excellent feasibility of the XFH measurements and the new data analysis by reviewing their applications to some functional materials with complex crystal structures, such as a determination of impurity sites in a Mn‐doped Bi 2 Te 3 topological insulator, a spin‐state selective structure in Fe 65 Ni 35 Invar alloy, and a lattice distortion in Fe chalcogenide room‐temperature superconductor …”

“…To solve this problem of an equation for an underdetermined system, Matsushita recently developed a new algorithm, named SPEA-L1 (the scattering pattern matrix extraction algorithm using L 1 regularized linear regression), [23] which is based on inverse problem and sparse modeling. [24] In this article, we present the excellent feasibility of the XFH measurements and the new data analysis by reviewing their applications to some functional materials with complex crystal structures, such as a determination of impurity sites in a Mndoped Bi 2 Te 3 topological insulator, [16] a spin-state selective structure in Fe 65 Ni 35 Invar alloy, [25] and a lattice distortion in Fe chalcogenide room-temperature superconductor. [26]…”

“…3D atomic images of Fe 65 Ni35 Invar alloy around the a) Fe and b) Ni atoms at 100 K, and c, d) those at 300 K. The dashed lines indicate the cubic unit cells, and the central atoms are located at the left-bottom corners. Reproduced with permission [25]. Copyright 2018, John Wiley & Sons, Ltd.www.advancedsciencenews.com www.pss-b.com produce a much larger thermal expansion unlike the Invar effect.…”

“…A structural model for the Invar effect suggested by the present XFH measurements at a) 100 K, and at 300 K b) without and c) with the positional fluctuations. Reproduced with permission [25]. Copyright 2018, John Wiley & Sons, Ltd. www.advancedsciencenews.com www.pss-b.com 0 θ 70 in steps of 1.00 and 0 ϕ 360 in steps of about 0.3 , respectively.…”