Low Temperature Magnetoresistance and the Magnetic Phase Diagram of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>La</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ca</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>MnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Abstract

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.