78.
Carbon-doped Mn
3Ga thin films were grown on Si/SiO
2 substrates using rf magnetron sputtering technique. The tetragonal D0
22–type crystalline structure of ferrimagnetic Mn
3Ga is preserved on the Mn
3GaC
x films upon carbon concentrations up to
x = 0.5, whereas higher concentrations lead to the formation of the antiperovskite Mn
3GaC phase. Geometry optimization calculations using the density functional theory were performed on a 2 × 2 × 2 Mn
3GaC
0.25 supercell with C in different positions in order to find that the most stable position for the C is interstitial octahedral site. Magnetic
M(
H) loops show that saturation magnetization
Ms of Mn
3GaC
0.25 is enhanced to 200 kAm
−1 (from
Ms = 90 kAm
−1 for undoped films). The increase of the C concentration leads to a reduction of the Curie temperature from 770 K to ∼420 K at the same time that the lattice cell suffers an expansion. The enhancement of
Ms is explained in terms of a 90° ferromagnetic superexchange Mn-C-Mn interaction.
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