Magnetic/structural phase diagram of GaCFe 3− x Co x (0 ≤ x ≤ 3.0) were investigated systematically. It was found that the antiperovskite phase collapses at x = 0.90 and recovers again at x = 2.3 with Co doping. Along with this transformation, the ferromagnetic state in GaCFe 3 is suppressed and replaced by the reentrant spin-glass state (2.3 ≤ x ≤ 2.6) or enhanced magnetic fluctuations (2.7 ≤ x ≤ 3.0). Ac susceptibility and magnetic relaxation were adopted to validate this spin-glass state for x = 2.5. It indicates that the contractive lattice as well as the resultant enhanced magnetic couplings may be an important origin of the collapsed antiperovskite structure. Zero temperature coefficient of resistivity (TCR) was achieved by Co-doping where the sign of TCR changes from positive to negative across the room temperature. The optimized TCR ∼ 0.0346 ppm/K spanning 110 K are three orders of magnitude smaller than those of CuNMn 3 or GaCFe 3 . The physical mechanism was discussed.
