The structural and magnetic properties of NiMnSb films, 5-120 nm thick, grown on InGaAs/InP(001) substrates by molecular-beam epitaxy, were
studied by x-ray diffraction, transmission electron microscopy (TEM),
and ferromagnetic resonance (FMR) techniques. X-ray diffraction and TEM
studies show that the NiMnSb films had the expected half-Heusler
structure, and films up to 120 nm were pseudomorphically strained at
the interface, greater than the critical thickness for this system,
about 70 nm (0.6% mismatch to InP). No interfacial misfit dislocations
were detected up to 85 nm, however, relaxation in the surface regions
of films thicker than 40 nm was evident in x-ray reciprocal space maps.
TEM investigations show that bulk, planar defects are present beginning
in the thinnest film (10 nm). Their density remains constant but they
gradually increase in size with increasing film thickness. By 40 nm
these defects have overlapped to form a quasicontinuous network aligned
closely with < 100 > in-plane directions. The associated strain fields
and or compositional ordering from these defects introduced a reduction
in crystal symmetry that influenced the magnetic properties. The
in-plane and perpendicular FMR anisotropies are not well described by
bulk and interface contributions. In thick films, the in-plane uniaxial
and fourfold anisotropies increased with increasing film thickness. The
lattice defects resulted in a large extrinsic magnetic damping caused
by two-magnon scattering, an increase in the coersive field with
increasing film thickness, and a lower magnetic moment (3.6 Bohr
magnetons) compared to the expected value for the bulk crystals (4 Bohr
magnetons). (C) 2005 American Institute of Physics.