Structural and magnetic properties of GaN/Mn nanopowders prepared by an anaerobic synthesis route

A new oxygen-free molecular precursor system based on (i) ammonolysis in refluxing/liquid NH3 of selected mixtures of gallium tris(dimethyl)amide Ga(NMe2)(3) and manganese bis(trimethylsilyl) amide Mn [N(SiMe3)(2)](2) (Me = CH3, initial Mn-contents = 0.1, 5, 20, 50 at.%) followed by (ii) pyrolysis under flowing ammonia gas at 500, 700, and 900 degrees C afforded a range of nanocrystalline powders in the GaN/Mn system. The nanopowders were characterized mainly by powder XRD diffraction, FT-IR spectroscopy, Raman spectroscopy, SEM/EDX morphology examination, and XRF elemental analysis. Magnetization measurements as a function of magnetic field and temperature were carried out with a SQUID magnetometer. Structurally, the materials were shown to be single-phases based on the gallium nitride lattice. The presence of small quantities of residual amorphous Mn/N/Si/C species due to an incomplete transamination/removal of the trimethylsilylamide groups during ammonolysis was deduced from the XRF, FT-IR, Raman, and magnetization data. Magnetic properties for all nanopowders consistently pointed to a paramagnetic GaMnN phase with antiferromagnetic interactions among Mn-centers that under favorable circumstances reached the level of 3.8 at.% Mn. The paramagnetic phase was accompanied by a residual antiferromagnetic phase due to a facile oxidation in air of excessive Mn-containing by-products.