Impact of strain, pressure, and electron correlation on magnetism and crystal structure of Mn2GaC from first-principles

Abstract

the atomically laminated Mn 2 GaC has previously been synthesized as a heteroepitaxial thin film and found to be magnetic with structural changes linked to the magnetic anisotropy. Related theoretical studies only considered bulk conditions and thus neglected the influence from possible strain linked to the choice of substrate. Here we employ first principles calculations considering different exchangecorrelation functionals (PBE, PW91, PBEsol, AM05, LDA) and effect from use of + U methods (or not) combined with a magnetic ground-state search using Heisenberg Monte Carlo simulations, to study influence from biaxial in-plane strain and external pressure on the magnetic and crystal structure of Mn 2 GaC. We find that PBE and PBE + U, with U eff ≤ 0.25 eV, gives both structural and magnetic properties in quantitative agreement with available experimental data. our results also indicate that strain related to choice of substrate or applied pressure is a route for accessing different spin configurations, including a ferromagnetic state. Moreover, the easy axis is parallel to the atomic planes and the magnetocrystalline anisotropy energy can be increased through strain engineering by expanding the in-plane lattice parameter a. Altogether, we show that a quantitative description of the structural and magnetic properties of Mn 2 Gac is possible using pBe, which opens the way for further computational studies of these and related materials. In the 1960s, Nowotny and coworkers 1,2 discovered a family of inherently atomically laminated materials, which decades later were coined MAX phases. It is a ternary phase with the general formula M n+1 AX n (n = 1-3) where M is a transition metal (e.g. M = Ti, Cr, Mo, Zr), A is typically a group 13 to 16 element (e.g. A = Al, Si, Ga, Ge), and X is carbon or nitrogen. The material family, however, did not receive much attention until the mid-1990s and early 2000s when Ti 3 SiC 2 3 and Ti 4 AlN 3 4,5 , respectively, was demonstrated to possess a unique combination of metallic and ceramic characteristics. Since then, MAX phases have been synthesized both as bulk material and in thin film form, and have been shown to exhibit extraordinary physical, chemical, electrical and mechanical properties 6. Due to this, the MAX phases are being considered for protective coatings, electrical contacts, sensors, and high-temperature structural applications. They are also used as precursors for MXenes, their two-dimensional (2D) counterparts exhibiting extraordinary properties and are considered for a host of different applications 7-9. The first experimental evidence of magnetic MAX phases were quaternary Mn-doped Cr 2 GeC 10-12 , Cr 2 GaC 13-17 and Cr 2 AlC 14,18,19 followed by (Mo,Mn) 2 GaC 20,21 and (V,Mn) 3 GaC 2 22. Examples of ternary MAX phases with demonstrated magnetic properties are Cr 2 AlC 23,24 , Cr 2 GeC 11,24 , Cr 2 GaC 13,25 , Cr 2 GaN 25 , and Mn 2 GaC 26-29. The Cr-based phases have all been made in bulk form and as thin films, whereas Mn 2 GaC have been synthesized in thin film form...

Mn2C MXene functionalized by oxygen is a semiconducting antiferromagnet and an efficient visible light absorber

“…We can observe quite flat bands around the Fermi level and an indirect band gap with the smallest energy transition being from the Γ point to near the K point. Based on the recommended values of the Hubbard correction U for the Mn-based MXenes from previous studies, 45,54,56 we conclude from band structures (Fig. S11, ESI†) and band gaps (Table S3, ESI†) that PBE+ U ( U = 3 eV) corresponds well with a non-empiric SCAN approach without any U correction.…”

“…As has been recently shown in multiple studies, even the precursor MAX phase Mn 2 GaC has an AFM ground-state when more complex spin motifs are taken into account. [18][19][20]54 The same result holds even for the clean Mn 2 C sheet, although both the MAX phase and Mn 2 C are conductors. 27,55,56 The semiconducting behavior is therefore only achieved by oxygen termination.…”

Asymmetric Interfaces in Epitaxial Off-Stoichiometric Fe3+xSi1−x/Ge/Fe3+xSi1−x Hybrid Structures: Effect on Magnetic and Electric Transport Properties

“…We also analysed the epitaxial stress in the epilayer and in the crystallites of the polycrystalline layer of the Fe-Si alloy. Changing the chemical composition within the trilayers based on ferromagnetic Fe x (Si 1− y Ge y ) alloys can be used to tune the epitaxial stress and thereby the electronic structure and, as a result, the functional properties of the material [ 27 , 28 , 29 ].…”

On the formation mechanisms and properties of MAX phases: A review

“…Novoselova et al [130] observed a first order magnetic phase transition at 214 K from AFM at higher temperatures to a non-collinear AFM spin structure at lower temperatures, with the magnetostriction changing sign at this magnetic phase transition in a Mn 2 GaC film prepared by magnetron sputtering. It has been theoretically proven by Dahlqvist et al [131,132] that the magnetic states and structural parameters of Mn 2 GaC can be manipulated through controlling the temperature, the magnetic field or the applied pressure. The temperature and magnetic field dependence of magnetic properties has also been studied for some solid solutions such as (Cr 0.5 Mn 0.5 ) 2 GaC, (Mo 0.5 Mn 0.5 ) 2 GaC, (Cr 0.5 Mn 0.5 ) 2 AuC, etc [133,134], suggesting new pathways for tuning magnetism of MAX phases.…”

“…Related research to date is still focused on the prediction, discovery and determination of the fundamental magnetic properties of MAX phases and their solid solutions. However, the observed tunability of the magnetic properties by controlling the atomic configuration of alloying atoms on the M-site in simulations, by introducing multiple alloying elements on the A-site in experiments, and by controlling the temperature, the magnetic field or the applied pressure in both simulations and experiments, will guide the development of magnetic MAX phases and their solid solutions with promising properties for electronics, spintronics, refrigeration, etc [6,91,92,[130][131][132][133][134]140].…”