Effect of substitution of Mn and Ga atoms by Fe atom in the Mn2GaC MAX phase

https://doi.org/10.1016/j.jmmm.2022.169860Get rights and content

Highlights

  • Thermodynamically stable Mn1.875Fe0.125GaC, and Mn2Fe0.125 Ga 0.875C were found for the first time.

  • The doping of Ga-site by Fe in Mn2GaC leads to the forming of ferromagnetic ordering.

  • Large saturation magnetization is observed in ferromagnetic Mn2Fe0.125 Ga 0.875C.

  • The Curie temperature of Mn2Fe0.125 Ga 0.875C is larger than in pure Mn2GaC.

Abstract

The magnetic properties of ordered and disordered MAX-phase Mn2-xFe2xGaC and Mn2Ga1-xFexC (x = 12.5, 25, and 50 at.%) have been studied within DFT-GGA. The investigation of phase stability of M2AX phases is performed by comparing the total energy of MAX phases to that of the set of competitive phases for calculation of the phase formation enthalpy. At the small concentration of Fe atoms (x = 12.5 %) compound remains stable. We have found that introducing Fe atom at A-site leads to the forming of ferromagnetic phase with large magnetic moments on magnetic atoms and magnetization. Through detailed group-theoretical analysis we have obtained that only ferromagnetic ordering is possible when Fe atom ordering over Ga sites. The study of exchange constants shows that the out-of-plane Fe-Mn exchange gives the main contribution in appearance of ferromagnetic phase. The temperature dependences of magnetization reveal the increase of Curie temperature in Mn2GaC with Fe atom incorporated into Ga-site.

Introduction

The growing interest in the MAX phases is due to the unique set of properties inherent in these materials like high electrical and thermal conductivity, machinability, oxidation resistance, and high temperature mechanical properties [1], [2], [3]. The MAX phases with the general formula Mn+1AXn (n = 1–3) represent a family of layered compounds with a hexagonal structure (space group P63/mmc, No. 194) containing atomic layers of elements M, A, and X, stacked along the c direction. M is a transition metal, A is an A-group element, and X is either carbon or nitrogen [4], [5]. To date, a number of the MAX phases with early transition metals (M = Ti [5], [6], [7], V [6], [8], Cr [5], [6], [9], [10]) have been synthesized as bulk as well as the thin film. However, synthesis with late transition metals such as Mn, Fe, Co, Ni is largely unsuccessful. To date, only one the MAX phase with a magnetic transition metal, namely Mn2GaC, has been obtained. At the same time, the combination of the unique mechanical properties of the MAX phases with magnetic ones is of great interest [1], [2], [3], [4], [5]; therefore, attempts to synthesize such compounds do not stop. As has been shown in a number of works [11], [12], failures in the synthesis of magnetic MAX phases are largely related to their instability.

In the works [13], [14], [15], [16], another method was proposed for obtaining magnetic the MAX phases, namely, the replace the M- or A-site elements with a magnetic atom. This allows tuning the magnetic properties of MAX phases by changing the chemical composition and component in M- or A- atomic layers. One of the prospective candidates for the introducing is the Fe atom. So, recently some the MAX phases with Fe atom replacing A-site atom, namely M2FeC (M = Ta, Ti, Nb) [13], V2(Sn, Fe)C [14], Ti3(Al, Fe)C2 [15] and Mo2(Ga,Fe)C [16] were successfully synthesized. Authors obtained that introducing of Fe atom on A-site leads to the forming of ferromagnetic ordering in doped MAX phase and the increase of the magnetization and Curie temperature. However, despite of the Fe doping leads to the growth of saturation magnetization, it remains relatively small (Ms = 0.14 emu/g [14], 1.56 emu/g [15], 5.93–19.69 [13]).

In this work, we investigate the possibility of obtaining a MAX phase with two magnetic atoms: Mn and Fe. The paper is organized as follows. In Section 2, we give a short description of the calculation details, in Section 3.1. We discuss the effect of the composition on the magnetic properties of Mn- and Fe-based MAX phases; in Sections 3.2 and Section 3.3. We study the phase stability and magnetic properties of ordered and disordered MAX phase with Fe being incorporated on M- and A-site, correspondingly; in Section 3.4 the results of the group-theoretical analysis of possible magnetic ordering in Mn2GaC with Fe incorporated into Ga-site are given; Section 3.5 devoted to the Monte-Carlo simulation of Fe-doped Mn2GaC MAX phase. In the last Section, we draw conclusions.

Section snippets

Calculation details

All ab initio calculations presented in this paper are performed using the Vienna ab initio simulation package (VASP) [17] with projector augmented wave (PAW) pseudopotentials [18], [19]. The valence electron configurations 3d64s2 and 3d54s2 were taken for Fe and Mn atoms, 3d104s24p1 3s23p2 and 2s22p4 for Ga and C atoms, correspondingly. The calculations are based on the density-functional theory with the Perdew-Burke-Ernzerhoff (PBE) parameterization [20] of the exchange–correlation functional

Manganese and iron-based magnetic MAX phases

As mentioned in the Introduction, out of the whole variety of possible magnetic MAX phases, only Mn2GaC is an experimentally synthesized and well-studied stable magnetic MAX phase. The main reason for the failure of experimental synthesis is the instability of these compounds as it was shown within the density functional theory and phase diagram calculations in Refs [11], [12], [30], [31], [32]. In our previous work [33] we have theoretically studied the possible magnetic M2AX phases based on

Conclusions

In summary, we have performed the study of the Fe doping effect on the stability and magnetic properties of the Mn2GaC MAX phase. We considered ordered Mn2-xFe2xGaC and Mn2FexGa1-xC MAX phases at three Fe concentration (x = 0.125, 0.25, 0.5). As the result, we found that up to a Fe concentration of x = 0.125 compounds remain stable. It was found that most significant effect appears with non-trivial substitution of Ga atoms by Fe. While the substitution of Mn by Fe does not lead to a pronounced

CRediT authorship contribution statement

Oksana N. Draganyuk: Software, Investigation, Formal analysis. Natalia G. Zamkova: Methodology, Investigation, Writing – review & editing, Formal analysis. Vyacheslav S. Zhandun: Conceptualization, Validation, Investigation, Writing – original draft, Writing – review & editing, Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The reported study was funded by Russian Foundation for Basic Research, Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science to the research project № 20-42-240004: “The effect of the composition, pressure, and dimension on the magnetic, electronic, optical, and elastic properties of the magnetic Mn+1AXn (M = Cr, Mn; Fe, A = Al, Ga, Si, Ge, P, In; X = C, N; n = 1-3) MAX-phases”. The calculations were performed with the computer resources of “Complex modeling and data

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