Ground-state instability of the Mott insulator Ca2RuO4:: Impact of slight La doping on the metal-insulator transition and magnetic ordering

Ca2RuO4 is a Mott system with a structurally driven metal-insulator transition at T-MI = 357 K and Neel temperature at T-N = 110 K. Slight substitution of trivalent La for bivalent Ca in Ca2RuO4 drastically reduces T-MI and the electrical resistivity, simultaneously precipitating robust ferromagnetism in the antiferromagnetic host. T-C is conspicuously and consistently lower than T-MI, suggesting that the metal-insulator transition is not driven by the magnetic instability. The La substitution:also results in a rapid increase in both the Pauli susceptibility and electronic specific heat coefficient, and:a crossover from hopping conductivity to disordered metallic behavior at low temperatures. These dramatic changes;underline the subtlety of the competition between the antiferromagnetic and ferromagnetic coupling:and a near degeneracy of the ground state in Ca2RuO4.