Magnetic properties of substitutional 3d transition metal impurities in silicon carbide -: art. no. 125204

Using the linearized muffin-tin orbital (LMTO) method within both the atomic sphere approximation and full potential (FP) implementations and within the local spin-density-functional method and a supercell approach, we study the magnetic properties of cubic (3C) silicon carbide (SiC) doped by first-row transition metals (TM's). The magnetic properties are found to depend strongly on the doping site. For substitution on the Si site, a nonmonotonic behavior of the magnetic moments with d state filling is found. This is due to the large hybridization of the TM d states with the neighboring dangling bonds, which leads to a larger crystal field than spin splitting. This leads to low-spin states. On the other hand, for the unrelaxed structures, substitution on the C site leads to large-spin states, following an atomiclike Hund's rule because of the weak hybridization with the surrounding dangling bonds. The relaxation effect, studied with FP-LMTO in selected cases, is large for the C site and small for the Si site. It leads to a suppression of the high magnetic moments for the C substitution. In any case, the calculated energies of formation indicate a strong preference for Si substitution, even when relaxation effects are included. In the case of neighboring pairs of TM dopants, there is generally a suppression of the magnetic moments, except for the Cr and Mn cases on the Si site. Ferromagnetic (FM) coupling is found to be preferred strongly for Cr. For Mn ferromagnetic coupling is found when relaxation is included. The tendencies towards ferromagnetic or antiferromagnetic (AFM) behavior are discussed in view of the Anderson-Hasegawa models of superexchange and double exchange. Thermodynamic considerations indicate that Cr and Mn doping on Si should be favorable. In fact, Si substitution would be preferred in the C-rich limit and neither Cr nor Mn is a strong carbide former. The strong energetic preference for FM over AFM ordering indicates possibly a high Curie temperature.