Easy-plane magnetic anisotropy of a single dopant in a single semiconductor nanowire

Abstract

The magnetic anisotropy of an isolated substitutional Co impurity in a single ZnO nanowire is studied by performing density-functional supercell calculations with the Hubbard U correction. The variation of the magnetic anisotropy energy with the location of the Co atom in different regions of the nanowire is explored. Contrary to usual expectation, it is found that single Co-doped ZnO nanowire possess an easy plane (as opposed to easy axis) of magnetization, which is neither parallel nor perpendicular to the nanowire axis; the orientation of the easy plane is determined by the local geometry around the dopant. Our results also show that the magnetic anisotropy energy is enhanced by almost an order of magnitude when the Co impurity moves to a surface site from an interior site. This enhancement is elucidated on the basis of local bonding characteristics, because a pronounced variation of the orbital moment of Co with the magnetization direction is observed only when Co is located at the nanowire surface. The complementary analysis of these findings shows that the magnetic anisotropy of a single dopant in a single nonmagnetic semiconductor nanowire can be directionally manipulated and substantially enhanced by controlling the local chemical environment of the dopant in the absence of magnetic coupling. Our findings thus imply that the directional control of magnetic anisotropy needs to be achieved for applications of magnetic ion doped semiconductor nanowires.