Low Temperature Magnetoresistance and the Magnetic Phase Diagram ofLa1−xCaxMnO3
The complete phase diagram of a ``colossal'' magnetoresistance material ( ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$) was obtained for the first time through magnetization and resistivity measurements over a broad range of temperatures and concentrations. Near $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.50$, 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 $\ensuremath{\sim}30%$ ${T}_{N}$ at $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.50$. An unexpectedly large magnetoresistance is seen at low temperatures in the FM phase, and is largely attributed to unusual domain wall scattering.