Element-selective elastic properties of Fe₆₅Ni₃₅ Invar alloy and Fe₇₂Pt₂₈ alloy studied by extended X-ray absorption fine structure

ABSTRACT

We present the element-selective local structure analysis of ferromagnetic Fe${}_{65}$Ni${}_{35}$ Invar alloy and Fe${}_{72}$Pt${}_{28}$ alloy under high pressures as a recent application of nano-polycrystalline diamond (NPD) to extended X-ray absorption fine structure (EXAFS). The Invar effect is a phenomenon where thermal expansion becomes nearly zero in a wide range of temperatures. Fe${}_{72}$Pt${}_{28}$ is an alloy exhibiting negative thermal expansion. Our EXAFS analysis successfully revealed significant differences in element-selective elastic properties between local structures around Fe and Ni/Pt. The local structure around Fe has a smaller bulk modulus than that of Ni. Hence, the more compressive behavior around Fe is responsible for the anomalously soft elastic property that is characteristic of Invar alloy. In the case of Fe${}_{72}$Pt${}_{28}$, Fe has a smaller bulk modulus than Pt; however, the difference in bulk modulus in the ferromagnetic phase is small compared with that of Invar alloy. We also report different trends of pressure-induced decrease in Debye-Waller factors toward paramagnetic phases.

KEYWORDS:

• Invar effect
• nano-polycrystalline diamond
• extended X-ray absorption fine structure (EXAFS)
• element-selective compression curves

Acknowledgments

The authors express their gratitude to Prof. H. Maruyama for supplying high quality samples. The XAS measurements were performed at SPring-8 with the approval of PRC-JASRI (Nos. 2017B1304, 2017B1974, 2018B1355, and 2019A1530).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The studies presented herein were partially supported by Grant-in-Aid for Scientific Research on Innovative Areas (Grant Number 15H05829) and JSPS KAKENHI (Grant Number 17K05518).