Influence of topology on the phase transition of a ferromagnetic metal.

The topological ferromagnet CoS 2 exhibits an anhysteretic, weakly first-order transition at the Curie temperature of 119.8 K with a tricritical point µ 0 H tcp at 0.034 T. Magnetic symmetry and the mixing of majority and minority spin e g bands at a subband crossing just above the Fermi level produce a topological component of the magnetization that leads to a negative M 3 term in the Landau free energy. The position of the Fermi level relative to the subband crossing is critical for controlling the order of the transition. Hole doping in Co 0.89 Fe 0.11 S 2 drains the minority-spin e g pocket and results in a normal second-order phase transition. Electron doping in Co 0.94 Ni 0.06 S 2 raises the Fermi level toward the subband gap, producing a strongly first-order transition with 15 K hysteresis. Our results demonstrate a relation between topological electronic structure and thermal hysteresis at the Curie point, which may help in the search for magnetocaloric materials.