Calculated electronic and magnetic structure of rutile phase V1−xCrxO2

Abstract

Recent experiments indicate that films of V1−xCrxO2 may be obtained which retain the tetragonal rutile phase to low temperature. In order to better understand this system we have calculated its electronic structure using density functional theory in the generalized gradient approximation and density functional theory with empirical on-site Coulomb correlations (LDA+U). Within these approximations we find that the ground state of rutile phase V1−xCrxO2 is quite simple. Both V and Cr are in the +4 state, implying that the V and Cr ions have moments of 1μB and 2μB, respectively. Similar to CrO2, V1−xCrxO2 is predicted to be ferromagnetic and half-metallic. Our results appear to be consistent with the experimental observations that VO2 is paramagnetic and metallic for temperatures above 340 K where it is stable. It is not clear, however, that these results are completely consistent with recent experimental observations of ferromagnetism at low temperature in V1−xCrxO2 for x=0.1 and x=0.2.

Testing the Jacob's ladder of density functionals for electronic structure and magnetism of rutileVO2

“…The obtained total energies of spin-polarized (FM and AFM) states are always lower than that of the spincompensated PM state. For example, Williams et al [57] have calculated the energy differences of R-VO 2 in magnetic states (AFM and FM) with respect to the non-spin polarized state. It was found that the energies of FM and AFM phases are lowered by 135 meV/ VO 2 and 56 meV/VO 2 using the PBE GGA, compared to the non-spin-polarized phase.…”

“…One should note that, in the works of Williams and coworkers [57], both the lattice constants and atomic positions were fixed to their experimental values. However, the atomic positions are allowed to relax in our calculations.…”

Competition between ferromagnetism and antiferromagnetism in the rutileCr1−xVxO2system

“…In order to understand the effects of vanadium substitution on CrO 2 [15], which both predicted a half-metallic FM ground state. The initial calculations were performed in simple six-atom rutile cells with the experimental crystal structure (Ref.…”

“…However, thin films grown on a (001) Al 2 O 3 substrate are stable in the rutile phase down to 100 K, and the semiconductor-insulator transition is suppressed [17,19]. DFT calculations by Williams et al [15] predicted these stabilized rutile V x Cr 1−x O 2 compounds to be not only ferromagnetic, but also half-metallic. Nevertheless, a later experimental study revealed V 0.82 Cr 0.18 O 2 to be a ferromagnetic insulator [19].…”

“…The magnetic ground state of the rutile-structured VO 2 , which is not experimentally obtainable due to the MIT, is still under debate. Many DFT methods predict a half-metallic * Corresponding author: maarit.karppinen@aalto.fi ferromagnetic ground state for rutile VO 2 similar to that of CrO 2 [15,16]. Room-temperature ferromagnetism was recently discovered in thin films of rutile-structured VO 2 partially substituted with chromium [17].…”