Investigation of the insulator to half-metal transition in Cr-doped ZnO at low temperature (19 K) wurtzite structure

SARAJIT BISWAS

Abstract


The structural, electronic and magnetic properties of pure and Cr doped ZnO with a low temperature (19 K) wurtzite structure were calculated employing the density functional theory (DFT) as implemented in the tight-binding linearized-muffin-tin orbital (TB-LMTO) method. Pure ZnO is observed a nonmagnetic insulator, in which all the Zn-3d orbitals are found occupied and electrons are perfectly paired in each orbital causing nonmagnetic nature of pure ZnO. But Cr doping in ZnO significantly changes its structural, electronic and magnetic properties. This material encounters nonmagnetic insulator to ferromagnetic half-metal with minute structural distortions at 50% Cr substitution (Zn0.5Cr0.5O) for Zn. It is revealed in this study that Zn0.5Cr0.5O is metallic for majority spin species and insulating for minority spin species with a semiconducting gap ~3.5 eV.  Due to the strong electron correlation effect, three Cr-t2g orbitals become fully occupied by three Cr-3d electrons while remaining single electron is shared by two eg ¬orbitals in the close vicinity of the Fermi level. This sharing of the single electron by two eg orbitals is responsible for the metallic behaviour of Zn0.5Cr0.5O. The parallel alignment of unpaired electrons in the Cr-3d orbitals is responsible for ferromagnetism of this material.

Keywords


Wurtzite structure; Density functional theory (DFT); Ferromagnetism, Half-metal; Local spin density approximation (LSDA)

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References


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