High-temperature anti-Invar behavior of γ -Fe precipitates in Fe x Cu 100 − x solid solutions: Ferromagnetic phases

S. L. Palacios, R. Iglesias, D. Martínez-Blanco, P. Gorria, M. J. Pérez, J. A. Blanco, A. Hernando, and K. Schwarz

Phys. Rev. B 72, 172401 – Published 1 November 2005

ABSTRACT

High-temperature magnetization and neutron diffraction measurements on metastable ${\mathrm{Fe}}_x{\mathrm{Cu}}_{100-x}$ solid solutions have recently shown to imply that $\gamma$-Fe precipitates present ferromagnetic anti-Invar behavior. For this reason, we have studied the ferromagnetic phases of $\gamma$-Fe in moment-volume parameter space, using the general potential linearized-augmented plane-wave method and the fixed spin moment procedure in order to calculate the corresponding total energy. We find that only two ferromagnetic phases (one related to a low-spin state and the other to a high-spin state) can exist and even coexist in limited volume ranges (3.55-3.59 Å). Hence, our results provide a “revisited” version of the local spin density calculations used in the early article by Moruzzi et al. [Phys. Rev. B 34, 1784 (1986)]. In addition, the fixed spin moment method—using an energy-moment-volume space representation—allows us to conclude that the high-spin state is the ground state of the $\gamma$-Fe precipitates, as the anti-Invar behavior is an intrinsic property of these states. This simple scenario seems to adequately describe the perplexing phenomenology recently observed on ${\mathrm{Fe}}_x{\mathrm{Cu}}_{100-x}$ solid solutions.

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• Received 19 January 2005

https://sci-hub.tw/https://journals.aps.org/prb/abstract/10.1103/PhysRevB.72.172401

As is well known, at atmospheric pressure iron presents two different crystal structures, namely, the body centered cubic bcc and the face centered cubic fcc. At room temperature RT only the ferromagnetic bcc -Fe phase is stable, while at temperatures above the reversible martensite-austenite temperature TMA =1183 K, -Fe undergoes a discontinuous first-order phase transition into the fcc -Fe phase, which is stable up to 1665 K.