Low temperature magnetoresistance and the magnetic phase diagram of La_1-xCa_xMnO₃

The complete phase diagram of a "colossal" magnetoresistance material (La_1-xCa_xMnO₃) was obtained for the first time through magnetization and resistivity measurements over a broad range of temperatures and concentrations. Near x = 0.50, the ground state changes from a ferromagnetic (FM) conductor to an antiferromagnetic (AFM) insulator, leading to a strongly first order AFM transition with supercooling of ∼30% T_N at x = 0.50. An unexpectedly large magnetoresistance is seen at low temperatures in the FM phase, and is largely attributed to unusual domain wall scattering.