Small-angle neutron scattering study of the steplike magnetic transformation inPr0.70Ca0.30MnO3

Abstract

Small-angle neuron scattering (SANS) magnetic and electrical transport measurements were performed to study a single crystal of ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$, a colossal magnetoresistive material. While the magnetic-field-induced transformation of this phase separated compound consisting of an antiferromagnetic insulating (AFI) phase and a ferromagnetic insulating (FI) phase is continuous at high temperature (above $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$), at lower temperature a steplike transformation is observed (around $5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$). Macroscopic magnetization measurements and SANS indicate that this transformation occurs by the formation of mesoscopic ferromagnetic metallic (FM) domains in the AFI phase and, eventually, in the FI phase. Although above $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ this transformation is continuous, below $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ a magnetization step marks the abrupt transition from a large-scale FI/AFI phase separation, AFI containing 1% of small FM clusters, to a large-scale phase separation between AFI, FI, and FM phases. Our results suggest that relaxation of elastic strains inherent to the coexistence of these different phases plays a crucial role in the mechanism of these transformations. The occurrence of magnetization steps could result from an intrinsic behavior of the AFI phase at low temperature.