Mn-Doped GaN Thin Films

The above discussion does not explain why in certain experiments the coupling between Mn atoms exhibits antiferromagnetism or spin glass behavior. We note that most of these experiments involve thin films. It is, therefore, important to understand if the magnetic behavior of Mn on surfaces and in thin films is fundamentally different from that in the bulk. For example, do Mn atoms prefer to reside on the surface, do they prefer to cluster, and does the Mn-Mn distance depend upon the crystallographic orientation of the surface In the following we discuss these aspects. 

To study the site preference of a Mn atom, we have first replaced one Ga atom with Mn on the surface layer, the second layer and the third layer on either side of the slab. It was found that Mn atom prefers to reside on the surface site which lies 1.37 and 1.54 eV lower than that of the second and third layer, respectively. This is consistent with the 

To understand the physics involved, we checked the changes in bond lengths. Due to relaxation, the bond lengths near the film surface 

In order to study if the magnetic coupling between Mn atoms depends upon the orientation of the thin film surface, we have considered (Ga, Mn)N thin film having wurtzite structure and [1010] orientation [38]. Note that the Mn-Mn distances may depend upon the surface orientation and hence may affect the magnetic ordering between them. 

To study the effect of the Mn concentration on the magnetic coupling between the Mn atoms, we performed extensive calculations on the GaN slabs with different thickness along the [1010] direction, as well as the 

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