Exchange interactions in paramagnetic amorphous and disordered crystalline<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>CrN</mml:mi></mml:math>-based systems

Lindmaa, Alexander; Lizárraga, Raquel; Holmström, Erik; Abrikosov, Igor A.; Alling, Björn

doi:10.1103/physrevb.88.054414

Cited by 29 publications

(30 citation statements)

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“…A model of the complete disorder, however, is applicable if the temperature of the system (T ) is much higher than the strongest interaction J max ij of the classical Heisenberg Hamiltonian (T J max ij ). For CrN, the calculated exchange interactions [55] are found to be of the order of 150 K for realistic lattice displacements obtained from MD and it is only for the largest displacements that they get close to 300 K. This means that for CrN, T = 300 K is indeed larger than J max ij ∼ 150 K and we can confidently consider CrN to be in its PM state at 300 K and treat it within DLM-MD already at this temperature. We note that the temperature T as used in this article thus refers to the temperature of the atoms and not that of the magnetic subsystem.…”

Section: B Details Of Dlm-md Simulationsmentioning

confidence: 78%

“…The other elastic constants (in GPa) are C 22 = C 11 = 659,C 33 = 616,C 13 = C 23 = 93,C 44 = C 55 = 144, and C 66 = 154, respectively. The relatively small difference between AFM and PM calculations can be attributed to relatively weak magnetic exchange interactions in B1 CrN [55]. One should expect a substantially larger effect in systems with higher Néel or Curie temperature.…”

Section: A Single-crystal Elastic Constantsmentioning

confidence: 87%

“…However, one should bear in mind that due to magnetic disorder the cubic symmetry of the supercell is broken and all the elements of the elastic matrix, 55 , and C 66 are not identical and need to be calculated. Then we use the projection technique to determine average cubic elastic constants [31] of the simulated cubic crystal viā…”

Section: Finite Temperature Elastic Constants From Static Calculatmentioning

confidence: 99%

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Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture fromab initiomolecular dynamics calculations

et al. 2016

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We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and ab initio molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance the efficiency of the simulations of elastic properties using the recently introduced method: symmetry imposed force constant temperature-dependent effective potential (SIFC-TDEP). We have chosen cubic paramagnetic CrN as a model system. This is done due to its technological importance and its demonstrated strong coupling between magnetic and lattice degrees of freedom. We have studied the temperature-dependent single-crystal and polycrystalline elastic constants of paramagentic CrN up to 1200 K. The obtained results at T = 300 K agree well with the experimental values of polycrystalline elastic constants as well as the Poisson ratio at room temperature. We observe that the Young's modulus is strongly dependent on temperature, decreasing by ∼14% from T = 300 K to 1200 K. In addition we have studied the elastic anisotropy of CrN as a function of temperature and we observe that CrN becomes substantially more isotropic as the temperature increases. We demonstrate that the use of Birch law may lead to substantial errors for calculations of temperature induced changes of elastic moduli. The proposed methodology can be used for accurate predictions of mechanical properties of magnetic materials at temperatures above their magnetic order-disorder phase transition.

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Section: B Details Of Dlm-md Simulationsmentioning

confidence: 78%

Section: A Single-crystal Elastic Constantsmentioning

confidence: 87%

Section: Finite Temperature Elastic Constants From Static Calculatmentioning

confidence: 99%

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Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture fromab initiomolecular dynamics calculations

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“…The focus is instead of finding possible magnetic ground-state configurations using a Heisenberg Hamiltonian H = − (i = j )J ij e i · e j , where J ij is the MEI between pairs of super-moments (i, j ), with unit vectors e i and e j along the local magnetic moment at site i and j, represented by a chain of super-moments. We derived the exchange interactions J ij , i.e., MEI, between the supermoments of the Heisenberg Hamiltonian for the first four supermoment interlayer coordination shells at various volumes, by using the magnetic Connolly-Williams structure inversion method [62,63] in combination with energyvolume data. The volume dependence J ij is displayed in Fig.…”

Section: Heisenberg Monte Carlo Simulationsmentioning

confidence: 99%

Magnetically driven anisotropic structural changes in the atomic laminateMn2GaC

et al. 2016

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Inherently layered magnetic materials, such as magnetic M n+1 AX n (MAX) phases, offer an intriguing perspective for use in spintronics applications and as ideal model systems for fundamental studies of complex magnetic phenomena. The MAX phase composition M n+1 AX n consists of M n+1 X n blocks separated by atomically thin A-layers where M is a transition metal, A an A-group element, X refers to carbon and/or nitrogen, and n is typically 1, 2, or 3. Here, we show that the recently discovered magnetic Mn 2 GaC MAX phase displays structural changes linked to the magnetic anisotropy, and a rich magnetic phase diagram which can be manipulated through temperature and magnetic field. Using first-principles calculations and Monte Carlo simulations, an essentially one-dimensional (1D) interlayer plethora of two-dimensioanl (2D) Mn-C-Mn trilayers with robust intralayer ferromagnetic spin coupling was revealed. The complex transitions between them were observed to induce magnetically driven anisotropic structural changes. The magnetic behavior as well as structural changes dependent on the temperature and applied magnetic field are explained by the large number of low energy, i.e., close to degenerate, collinear and noncollinear spin configurations that become accessible to the system with a change in volume. These results indicate that the magnetic state can be directly controlled by an applied pressure or through the introduction of stress and show promise for the use of Mn 2 GaC MAX phases in future magnetoelectric and magnetocaloric applications.

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“…The magnetic direct cluster averaging method (MDCA), described in detail in paper IV, is a direct adaptation of DCA by Lindmaa et al, who used it to treat magnetism in chemically and topologically disordered phases [58]. In such phases, the signs and magnitudes of the exchange interactions may vary significantly even between pairs of atoms that would be equivalent in the ideal crystal lattice, due differences in the chemical environment or spatial separation.…”

Section: Magnetic Exchange Interactionsmentioning

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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Exchange interactions in paramagnetic amorphous and disordered crystallineCrN-based systems

Cited by 29 publications

References 44 publications

Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture fromab initiomolecular dynamics calculations

Finite-temperature elastic constants of paramagnetic materials within the disordered local moment picture fromab initiomolecular dynamics calculations

Magnetically driven anisotropic structural changes in the atomic laminateMn2GaC

Phase stability and physical properties of nanolaminated materials from first principles

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