Magnetic Fen+1ACn(n= 1, 2, 3, and A = Al, Si, Ge) phases: fromab initiotheory

Luo, Wei; Ahuja, Rajeev

doi:10.1088/0953-8984/20/6/064217

Cited by 32 publications

(31 citation statements)

References 16 publications

(16 reference statements)

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“…However, Mn 2 AlC is very close to thermodynamic stability with H cp being just +0.005 eV/atom. Here, the most competing phases, out of all the phases included, 23 are identified as Mn 3 AlC, MnAl, and C. Fe 2 AlC is found to be quite metastable with H cp = +0.116 eV/atom, and it should decompose into the inverse perovskite, Fe 3 AlC, 25,26 in combination with FeAl and C. The discrepancy with previously reported results on this system 14 highlights the need to include all competing phases in phase stability studies. The trend in increasing instability is continued with Co 2 AlC, where the most competitive phases are CoAl, Co, and C. As H cp is comparatively large for all phases with n = 2 and 3, they will not be further discussed in this work.…”

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confidence: 73%

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Magnetic nanoscale laminates with tunable exchange coupling from first principles

et al. 2011

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The M(n+1)AX(n) (MAX) phases are nanolaminated compounds with a unique combination of metallic and ceramic properties, not yet including magnetism. We carry out a systematic theoretical study of potential magnetic MAX phases and predict the existence of stable magnetic (Cr(1-x)Mn(x))(2)AlC alloys. We show that in this system ferromagnetically ordered Mn layers are exchange coupled via nearly nonmagnetic Cr layers, forming an inherent structure of atomic-thin magnetic multilayers, and that the degree of disorder between Cr and Mn in the alloy can be used to tune the sign and magnitude of the coupling

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confidence: 73%

“…13 However, to the best of our knowledge, none have experimentally been demonstrated to show magnetic behavior. The few theoretical studies available [14][15][16] have not been able to identify suitable thermodynamically stable candidates, and hence the task of predicting a stable magnetic MAX phase is still open.…”

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confidence: 99%

Magnetic nanoscale laminates with tunable exchange coupling from first principles

et al. 2011

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“…There is also room for exploring completely new directions in synthesis, such as to follow up on the highly speculative, but exciting, predictions of Luo et al [94] and Enyashin et al [95] and attempt to synthesize magnetic MAX phases (with M = Fe) and Ti 3 SiC 2 nanotubes, respectively.…”

Section: Discussionmentioning

confidence: 99%

The M+1AX phases: Materials science and thin-film processing

et al. 2010

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This article is a critical review of the M n+1 AX n phases ("MAX phases", where n =1, 2, or 3) from a materials science perspective. MAX phases are a class of hexagonal-structure ternary carbides and nitrides ("X") of a transition metal ("M") and an A-group element. The most well known are Ti 2 AlC, Ti 3 SiC 2 , and Ti 4 AlN 3 . There are ~60 MAX phases with at least 9 discovered in the last five years alone. What makes the MAX phases fascinating and potentially useful is their remarkable combination of chemical, physical, electrical, and mechanical properties, which in many ways combine the characteristics of metals and ceramics. For example, MAX phases are typically resistant to oxidation and corrosion, elastically stiff, but at the same time they exhibit high thermal and electrical conductivities and are machinable. These properties stem from an inherently nanolaminated crystal structure, with M n+1 X n slabs intercalated with pure A-element layers. The research on MAX phases has been accelerated by the introduction of thin-film processing methods.Magnetron sputtering and arc deposition have been employed to synthesize single-crystal material by epitaxial growth, which enables studies of fundamental materials properties. However, the surface-initiated decomposition of M n+1 AX n thin films into MX compounds at temperatures of 1000-1100 °C is much lower than the decomposition temperatures typically reported for the corresponding bulk material. We also review the prospects for low-temperature synthesis, which is essential for deposition of MAX phases onto technologically important substrates. While deposition of MAX phases from the archetypical Ti-Si-C and Ti-Al-N systems typically require synthesis temperatures of ~800 °C, recent results have demonstrated that V 2 GeC and Cr 2 AlC can be deposited at ~450 °C. Also, thermal spray of Ti 2 AlC powder has been used to produce thick coatings. We further treat progress in the use of first-principles calculations for predicting hypothetical MAX phases and their properties. Together with advances in processing and materials 3 analysis, this progress has led to recent discoveries of numerous new MAX phases such as Ti 4 SiC 3 , Ta 4 AlC 3 , and Ti 3 SnC 2 . Finally, important future research directions are discussed. These include charting the unknown regions in phase diagrams to discover new equilibrium and metastable phases, as well as research challenges in understanding their physical properties, such as the effects of anisotropy, impurities, and vacancies on the electrical properties, and unexplored properties such as superconductivity, magnetism, and optics. 4

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“…Previous phase stability studies focusing on MAX phases have often relied on incomplete sets of competing phases, leading to results that have not necessarily reflected the experimental data [32][33][34]. However, following Dahlqvist, Alling, and…”

Section: Finding Competing Phasesmentioning

confidence: 99%

Phase stability and physical properties of nanolaminated materials from first principles

Thore¹

2016

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The cover shows an exponential curve. It is a visual representation of Moore's lawGordon Moore's observation that the number of components, such as transistors, per integrated circuit doubles roughly every two years. The exponential increase in computational power that this has entailed has made computational materials science possible. Curiously enough, computational materials science is now an important driver of this increase, and, consequently, a driver of its own capabilities. Printed by LiU-tryck, Linköping 2016 AbstractThe MAX phase family is a set of nanolaminated, hexagonal materials typically comprised of three elements: a transition metal (M), an A-group element (A), and carbon and/or nitrogen (X). In this thesis, first-principles based methods have been used to investigate the phase stability and physical properties of a number of MAX and MAX-like phases.Most theoretical work on MAX phase stability use the constraint of 0 K conditions, due to the very high computational cost of including temperature dependent effects such as lattice vibrations and electronic excitations for all relevant competing phases in the ternary or multinary chemical space. Despite this, previous predictions of the existence of new MAX phases have to a large extent been experimentally verified. In an attempt to provide a possible explanation for this consistency, and thus help strengthen the confidence in future predictions, we have calculated the temperature dependent phase stability of Tin+1AlCn, to date the most studied MAX phases. We show that both the electronic and vibrational contribution to the Gibbs free energies of the MAX phases are cancelled by the corresponding contributions to the Gibbs free energies of the competing phases. We further show that this is the case even when thermal expansion is considered.We have also investigated the stability of two hypothetical MAX-like phases, V2Ga2C and (Mo1-xVx)2Ga2C, motivated by a search for ways to attain new two-dimensional MAX phase derivatives, so-called MXenes. We predict that it is possible to synthesize both phases. For x≤0.25, stability of (Mo1-xVx)2Ga2C is indicated for both ordered and disordered solid solutions on the M sublattice. For x=0.5 and x≥0.75, stability is only indicated for disordered solutions. The ordered solutions are stable at temperatures below 1000 K, whereas stabilization of the disordered solutions requires temperatures of up to 2100 K, depending on the V concentration.Finally, we have investigated the electronic, vibrational, and magnetic properties of the recently synthesized MAX phase Mn2GaC. We show that the electronic band structure is anisotropic, and determine the bulk, shear, and Young's modulus to be 157, 93, and 233 GPa, respectively, and Poisson's ratio to be 0.25. We further predict the magnetic critical order-disorder temperature of Mn2GaC to be 660 K. We base the predictions on Monte Carlo simulations of a bilinear Heisenberg Hamiltonian constructed from magnetic exchange interaction parameters derived using two different supe...

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Magnetic Fe_n+1AC_n(n= 1, 2, 3, and A = Al, Si, Ge) phases: fromab initiotheory

Cited by 32 publications

References 16 publications

Magnetic nanoscale laminates with tunable exchange coupling from first principles

Magnetic nanoscale laminates with tunable exchange coupling from first principles

The M+1AX phases: Materials science and thin-film processing

Phase stability and physical properties of nanolaminated materials from first principles

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