Solid Solubility and Magnetism upon Mn Incorporation in the Bulk Ternary Carbides Cr 2 AlC and Cr 2 GaC

J. Phys.: Condens. Matter

Rosén

2016

106

This review presents MAX phases (M is a transition metal, A an A-group element, X is C or N), known for their unique combination of ceramic/metallic properties, as a recently uncovered family of novel magnetic nanolaminates. The first created magnetic MAX phases were predicted using density functional theory through evaluation of phase stability, and subsequently synthesized as heteroepitaxial thin films. All magnetic MAX phases reported to date, in bulk or thin film form, are based on Cr and/or Mn, and they include (Cr,Mn)2AlC, (Cr,Mn)2GeC, (Cr,Mn)2GaC, (Mo,Mn)2GaC, and (V,Mn)3GaC2, Cr2AlC, Cr2GeC and Mn2GaC. A variety of magnetic properties have been found, such as ferromagnetic response well above room temperature and structural changes linked to magnetic anisotropy. In this paper, theoretical as well as experimental work performed on these materials to date is critically reviewed, in terms of methods used, results acquired, and conclusions drawn. Open questions concerning magnetic characteristics are discussed, and an outlook focused on new materials, superstructures, property tailoring and further synthesis and characterization is presented.

Section: Materials Synthesis a Synthesis Methodsmentioning

confidence: 99%

Section: Bulk Synthesismentioning

confidence: 99%

Magnetic MAX phases from theory and experiments; a review

Ingason

J. Phys.: Condens. Matter

Rosén

2016

106

“…There are few exceptions, however, wherein a solid solution contains a M element, that do not generally bond to Al, such as Zr in (Nb 0.8 ,Zr 0.2 ) 2 AlC, 20 and (Nb 0.6 ,Zr 0.4 ) 2 AlC, 21 or Mn in (Cr x ,Mn 1Àx ) 2 AlC. 22,23 In all these examples, however, the mole fraction of the non-Al bonding M element is less that 0.5 of the total M-content.…”

Section: Introductionmentioning

confidence: 99%

Experimental and theoretical characterization of ordered MAX phases Mo2TiAlC2 and Mo2Ti2AlC3

Anasori

Journal of Applied Physics

Halim

et al. 2015

250

180

Herein, we report on the phase stabilities and crystal structures of two newly discovered ordered, quaternary MAX phases-Mo 2 TiAlC 2 and Mo 2 Ti 2 AlC 3 -synthesized by mixing and heating different elemental powder mixtures of mMo:(3-m)Ti:1.1Al:2C with 1.5 m 2.2 and 2Mo: 2Ti:1.1Al:2.7C to 1600 C for 4 h under Ar flow. In general, for m ! 2 an ordered 312 phase, (Mo 2 Ti)AlC 2 , was the majority phase; for m < 2, an ordered 413 phase (Mo 2 Ti 2 )AlC 3 , was the major product. The actual chemistries determined from X-ray photoelectron spectroscopy (XPS) are Mo 2 TiAlC 1.7 and Mo 2 Ti 1.9 Al 0.9 C 2.5 , respectively. High resolution scanning transmission microscopy, XPS and Rietveld analysis of powder X-ray diffraction confirmed the general ordered stacking sequence to be Mo-Ti-Mo-Al-Mo-Ti-Mo for Mo 2 TiAlC 2 and Mo-Ti-Ti-Mo-Al-Mo-Ti-TiMo for Mo 2 Ti 2 AlC 3 , with the carbon atoms occupying the octahedral sites between the transition metal layers. Consistent with the experimental results, the theoretical calculations clearly show that M layer ordering is mostly driven by the high penalty paid in energy by having the Mo atoms surrounded by C in a face-centered configuration, i.e., in the center of the M nþ1 X n blocks. At 331 GPa and 367 GPa, respectively, the Young's moduli of the ordered Mo 2 TiAlC 2 and Mo 2 Ti 2 AlC 3 are predicted to be higher than those calculated for their ternary end members. Like most other MAX phases, because of the high density of states at the Fermi level, the resistivity measurement over 300 to 10 K for both phases showed metallic behavior. V C 2015 AIP Publishing LLC.

“…In 2013, three different magnetic MAX phases obtained through alloying between Cr and Mn on the M site were presented: (Cr 1Àx ,Mn x ) 2 GeC (x $ 0.25) by Ingason et al, 8 Cr 1Àx ,Mn x GaC (where 0 < x < 0.5) by Lin et al, 9 and (Cr 1Àx ,Mn x ) 2 AlC (x $ 0.16) by Mockute et al 10,11 These findings were followed by even more recent reports on these alloys. [12][13][14] Later, Ingason et al proceeded to synthesize Mn 2 GaC, 15 the first MAX phase with a hitherto unexplored M site element, Mn, since Nowotny's pioneering work. In the case of (Cr 1Àx ,Mn x ) 2 AlC, 10,11 (Cr 1Àx ,Mn x ) 2 GeC, 8 and Mn 2 GaC, 15 the successful thin film synthesis was prompted by predictions of thermodynamic phase stability based on a first-principles approach developed by Dahlqvist et al 16,17 In this work, we investigate selected physical properties of Mn 2 GaC, which, due to its recent discovery, is still largely unexplored.…”

Section: Introductionmentioning

confidence: 99%

First-principles calculations of the electronic, vibrational, and elastic properties of the magnetic laminate Mn2GaC

Thore

Journal of Applied Physics

Alling

et al. 2014

In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn 2 GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn-Ga-Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn 2 GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M 2 AC phases where M ¼ Ti, V, Cr, Zr, Nb, Ta, and A ¼ Al, S, Ge, In, Sn. V C 2014 AIP Publishing LLC.