Finite temperature elastic constants of paramagnetic materials within the disordered local moment picture from ab initio molecular dynamics calculations

Abstract

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 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 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.

1 table, 3 figures

References in corpus (5)

• Effect of magnetic disorder and strong electron correlations on the thermodynamics of CrN
• Phonon self-energy and origin of anomalous neutron scattering spectra in SnTe and PbTe thermoelectrics
• Thermal Anharmonic Effects in PbTe from First Principles
• Structural stability and thermodynamics of CrN magnetic phases from ab initio and experiment
• Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab-initio molecular dynamics

Cited by in corpus (3)

• Anomalous phonon lifetime shortening in paramagnetic CrN caused by magneto-lattice coupling: A combined spin and ab initio molecular dynamics study
• Temperature-dependent elastic properties of binary and multicomponent high-entropy refractory carbides
• Ab initio molecular dynamics of paramagnetic uranium mononitride (UN) using disordered local moments