Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

Abstract

We investigate the effect of an external magnetic field on the physical properties of the acceptor hole states associated with single Mn acceptors placed near the (110) surface of GaAs. Cross-sectional scanning tunneling microscopy images of the acceptor local density of states (LDOS) show that the strongly anisotropic hole wave function is not significantly affected by a magnetic field up to 6 T. These experimental results are supported by theoretical calculations based on a tight-binding model of Mn acceptors in GaAs. For Mn acceptors on the (110) surface and the subsurfaces immediately underneath, we find that an applied magnetic field modifies significantly the magnetic anisotropy landscape. However, the acceptor hole wave function is strongly localized around the Mn and the LDOS is quite independent of the direction of the Mn magnetic moment. On the other hand, for Mn acceptors placed on deeper layers below the surface, the acceptor hole wave function is more delocalized and the corresponding LDOS is much more sensitive on the direction of the Mn magnetic moment. However, the magnetic anisotropy energy for these magnetic impurities is large (up to 15 meV), and a magnetic field of 10 T can hardly change the landscape and rotate the direction of the Mn magnetic moment away from its easy axis. We predict that substantially larger magnetic fields are required to observe a significant field dependence of the tunneling current for impurities located several layers below the GaAs surface.

Electronic structure and magnetic properties of Mn and Fe impurities near the GaAs (110) surface

“…At the same time the spatial profile of the wavefunction associated with the top-most impurity level in the gap, is considerably extended and therefore sensitive to the orientation of the impurity magnetic moment. This situation is quite different from the case of the Mn acceptor 24 , whose wavefunction is strongly localized for a dopant on the surface (where the anisotropy is small) and extended for a dopant in the sublayers (where, however, the anisotropy is large). These special features of the Fe dopant will permit the manipulation of the Fe spin by means of an external magnetic field of few Tesla.…”

“…This is different from the case of Mn, where such manipulation was shown to be difficult since the large magnetic anisotropy energy (up to 15meV) of Mn in the subsurface layers would require extremely strong magnetic fields to change the direction of its magnetic moment. 24 The rest of the paper is organized as follows. In the next section In Sec.…”

“…The model does have some limitations, which are recognized and understood. 24 Other TM impurities in GaAs are less investigated and understood, and more refined microscopic theories are necessary. This is one of the motivations of the present work.…”

“…[2][3][4][5][6][7][8][9] The experimental advances have stimulated theoretical studies of individual magnetic impurities in semiconductors, based both on first-principles calculations [10][11][12][13][14][15] and microscopic tight-binding (TB) models. [16][17][18][19][20][21][22][23][24] Approaches based on the TB models are particularly convenient to explore the solotronics limit of dilute impurities in semiconductor hosts. For the specific case of Mn dopants on the (110) GaAs surface, TB models 16,17,[19][20][21][22]24 have provided a quantitative description of the electronic and magnetic properties of the associated acceptor states.…”

“…[16][17][18][19][20][21][22][23][24] Approaches based on the TB models are particularly convenient to explore the solotronics limit of dilute impurities in semiconductor hosts. For the specific case of Mn dopants on the (110) GaAs surface, TB models 16,17,[19][20][21][22]24 have provided a quantitative description of the electronic and magnetic properties of the associated acceptor states. Early work by Tang and Flatté 16 introduced a TB model for a single substitutional Mn impurity in bulk GaAs.…”