Supplemental Information
Tailoring magnetism of multifunctional MnxGa films with giant perpendicular
anisotropy
L. J. Zhu, D. Pan, S. H. Nie, J. Lu, J. H. Zhaoa)
State Key Laboratory of Superlattices and Microstructures,Institute of Semiconductors,
Chinese Academy of Sciences, P. O. Box 912, Beijing 100083, China
a)Author
to whom correspondence should be addressed;
Electronic mail: jhzhao@red.semi.ac.cn
dislocation
MnGa
GaAs
Supplamental Fig1. Cross-sectional IFFT-TEM image of MnGa/GaAs interface. The straight line guides the
position of the interface, ellipse guides the position where dislocation appears.
As show in Fig 1(g) in the revised manuscript, these films exhibit much short c-axis than
bulks with the same composition probably due to tensile strains from epitaxy on GaAs since
GaAs has longer a-axis (0.3988 nm) than MnGa bulk (0.3875~0.3927, ref 23). c first drops,
consistent with the trend in bulks (ref 14,23) and films on GaN (ref. 21); while it slowly
comes back toward bulk value when x further increases.
To make clear the composition-dependence of c here, let us first consider such two
factors: as x increases, (a) bulk c decreases, which mainly contributes the decreasing trend of
c to films; (b) bulk a slowly increases toward a-value of GaAs (ref 23), which contributes a
decreasing trend of tensile strains (or tetragonal distortion) to films, further decreasing the
departure from bulk valve c, so c should slowly come back toward bulk value as x increases
toward 3.0. However, just based on the two mutual compensated trends, it can not give a
derivation from the monotonically decreasing trend because the bulk a of MnxGa keeps
smaller than that of GaAs though a increases all the way as x increases. So there must be
some other reason that influences the strains，or tetragonal distortion, or a, such that has
influence on c. Actually, measured values of both a and c in the films should be greatly
affected by the level of dislocation formed during tensile strain relaxation. The similar
phenomenon was observed and discussed in the growth of FePt on TiN buffers and was
named “domain matching epitaxy”, please see Trichy et al, APL 92,102504(2008). In our
MnGa films, we also observed a high level of dislocation or “domain matching epitaxy”–like
growth as a result of much smaller a value of MnxGa without strain (bulk) than that of GaAs.
Supplemental Fig. 1 shows cross-sectional inverse fast Fourier transform (IFFT) transmission
electron microscopy (TEM) image of MnGa/GaAs interface, from which a very high level
dislocation of lattice can be found. However, the composition dependence of tensile strain
relaxation through the dislocation is rather a complicated process. The detailed studies are
beyond the scope of this letter. For summary, the non-monotonic composition dependence of
c should be attributed to a combination of (a) x-induced c decrease in absence of consideration
of strains; (b) x-induced a increase, further results in decrease of minus departure of c from
bulk values; (c) complicated x-dependence of a and c induced by complicated x-dependence
of tensile strain relaxation. However, detailed studies to quantitatively make clear how much
on earth the three factors respectively determine the x-dependence of c, are beyond the scope
of this letter.