Formation of L10 Ordering in FeNi by Mechanical Alloying and Field-Assisted Heat Treatment: Synchrotron XRD Studies

Shuvam Mandal; Ajit Panigrahi; Ashutosh Rath; Matthias Bönisch; Pradyut Sengupta; Mayadhar Debata; Suddhasatwa Basu

doi:10.1021/acsomega.2c07869

Formation of L1₀ Ordering in FeNi by Mechanical Alloying and Field-Assisted Heat Treatment: Synchrotron XRD Studies

ACS Omega. 2023 Apr 10;8(15):13690-13701. doi: 10.1021/acsomega.2c07869. eCollection 2023 Apr 18.

Authors

Shuvam Mandal^{1

2}, Ajit Panigrahi^{1

2}, Ashutosh Rath^{1

2}, Matthias Bönisch³, Pradyut Sengupta^{1

4}, Mayadhar Debata^{1

2}, Suddhasatwa Basu^{1

2

5}

Affiliations

¹ CSIR-Institute of Minerals and Materials Technology, Bhubaneswar 751013, India.
² Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
³ Department of Materials Engineering, KU Leuven, Leuven 3001, Belgium.
⁴ Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India.
⁵ Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India.

Abstract

L1₀-ordered FeNi, tetrataenite, found naturally in meteorites is a predilection for next-generation rare-earth free permanent magnetic materials. However, the synthesis of this phase remains unattainable in an industrially relevant time frame due to the sluggish diffusion of Fe and Ni near the order-disorder temperature (593 K) of L1₀ FeNi. The present work describes the synthesis of ordered L1₀ FeNi from elemental Fe and Ni powders by mechanical alloying up to 12 h and subsequent heat treatment at 623 K for 1000 h without a magnetic field and for 4 h in the presence of 1.5 T magnetic field. Also, to address the ambiguity of L1₀ phase identification caused by the low difference in the X-ray scattering factor of Fe and Ni, synchrotron-based X-ray diffraction is employed, which reveals that 6 h milling is sufficient to induce L1₀ FeNi formation. Further milling for 12 h is done to achieve a chemically homogeneous powder. The phase fraction of L1₀-ordered FeNi is quantified to ∼9 wt % for 12 h milled FeNi, which increases to ∼15 wt % after heat treatment. Heat treatment of the milled powder in a magnetic field increases the long-range order parameter (S) from 0.18 to 0.30. Further, the study of magnetic properties reveals a decrease in magnetic saturation and a slight increase in coercivity with the increase in milling duration. At the same time, heat treatment in the magnetic field shows a considerable increase in coercivity.