Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from<i>ab initio</i>molecular dynamics

Shulumba, Nina; Alling, Björn; Hellman, Olle; Mozafari, Elham; Steneteg, Peter; Odén, Magnus; Abrikosov, Igor A.

doi:10.1103/physrevb.89.174108

Cited by 51 publications

(68 citation statements)

References 37 publications

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“…Unfortunately, an evaluation of the relative importance of magnetic and vibrational disorder requires full-scale free-energy calculations for a magnetically disordered system, which cannot be carried out within the theoretical framework suggested here. Shulumba et al [67] proposed a technique that allows one to achieve this goal and demonstrated that the magnetic disorder represents the major contribution, with respect to a vibrational one, for the description of phase stability of paramagnetic CrN. Good agreement of our calculations for the solubility product with the experiment may indicate that the situation is similar for the system considered in this paper.…”

Section: B Impurity Solution Enthalpiessupporting

confidence: 57%

Ab initiocalculation of the solution enthalpies of substitutional and interstitial impurities in paramagnetic fcc Fe

2014

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Section: B Impurity Solution Enthalpiessupporting

confidence: 57%

Ab initiocalculation of the solution enthalpies of substitutional and interstitial impurities in paramagnetic fcc Fe

2014

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“…However, in their study, the full vibrational free energy, including vibrational entropy was not calculated. An important improvement to the method is made in the work by Shulumba et al, where a combination of DLM-MD and TDEP was used to study vibrational free energy and phase stability of CrN [16]. In their treatment, the magnetic and vibrational degrees of freedom are coupled through the forces from DLM-MD.…”

Section: Introductionmentioning

confidence: 99%

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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“…Nevertheless, explicit DFT studies including anharmonic and magnetic effects, such as DLM molecular dynamics, are attractive but so far lacking for bcc Fe. A recent application to CrN revealed a good agreement between SSA and DLM molecular dynamics [30,31].…”

Section: Fig 2 (Color Online)mentioning

confidence: 99%

Temperature Dependent Magnon-Phonon Coupling in bcc Fe from Theory and Experiment

et al. 2014

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An ab initio based framework for quantitatively assessing the phonon contribution due to magnonphonon interactions and lattice expansion is developed. The theoretical results for bcc Fe are in very good agreement with high-quality phonon frequency measurements. For some phonon branches, the magnonphonon interaction is an order of magnitude larger than the phonon shift due to lattice expansion, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature. The framework closes the previous simulation gap between the ferro-and paramagnetic limits. DOI: 10.1103/PhysRevLett.113.165503 PACS numbers: 63.20.K-, 63.20.dd, 63.20.dk, 75.50.Bb An understanding of the mutual interaction between different temperature-induced excitations in solids is a pivotal challenge for the simulation of thermodynamic properties of many materials. Experimental studies of phonons at elevated temperatures can help elucidate magnon-phonon coupling. Neutron scattering experiments of phonon dispersions have provided important data at selected temperatures [11]. Nuclear resonant inelastic x-ray scattering measurements are more amenable for showing thermal trends with measurements at many temperatures, and we have recently performed nuclear resonant inelastic x-ray scattering measurements of the phonon density of states of bcc Fe at 38 temperatures through the Curie transition [12]. Nonharmonic changes in the phonon DOS and vibrational entropy were found to track the change in magnetization with temperature. Since experimental analysis of phonon DOS broadening suggests explicit anharmonic contributions from phonon-phonon interactions to be an order of magnitude smaller, these new results are suggestive of large magnon-phonon interactions in bcc Fe.Parameter-free electronic structure calculations like density functional theory (DFT) in principle provide access to interatomic forces, spin-polarized energetics, and their interactions. Force-constant calculations and spin simulations have indeed been performed for decades [10,13]. However, most studies have been restricted to separate investigations of the two effects, whereas their mutual coupling could only be addressed in recent years [1,[14][15][16]. The T ¼ 0 K limit of a ferromagnetic system like Fe is the most straightforward case [17] since calculating force constants for a single magnetic configuration with all spins pointing in the same direction is sufficient ("FM limit" in Fig. 1). The infinite-temperature limit of a paramagnetic system with fully disordered spins ("PM limit") is significantly more challenging due to the large magnetic phase space that needs to be sampled for an accurate prediction of the coupling. Significant progress has been made only very recently with techniques based on DLM and spin molecular dynamics [1,18], a spin-spiral approach [15], dynamical mean field theory [14], and a spin-space averaging procedure [16].Given the complexity of the problem, present day methods are currently applied only at very low temperat...

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Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN fromab initiomolecular dynamics

Cited by 51 publications

References 37 publications

Ab initiocalculation of the solution enthalpies of substitutional and interstitial impurities in paramagnetic fcc Fe

Ab initiocalculation of the solution enthalpies of substitutional and interstitial impurities in paramagnetic fcc Fe

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

Temperature Dependent Magnon-Phonon Coupling in bcc Fe from Theory and Experiment

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