Direct observation of magnetic domains in phase separatedNd0.7Ca0.3MnO3single crystals

Abstract

The magnetic properties of single-crystalline ${\mathrm{Nd}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ were studied with both macroscopic and microscopic probes. The magnetization shows large irreversibility behavior between zero-field-cooled and field-cooled data at low field, suggesting a phase separation driven by competition between ferromagnetic and antiferromagnetic phases. The scanning superconducting quantum interference device microscope observations under zero field gave clear evidence that the compound includes ferromagnetic regions as the ground state below $T_c.$ It was also found that two different phase-separated states appear, depending on temperature. At $T\sim 125\hspace{0.5em}\mathrm{K},$ weak but finite spontaneous magnetization develops, while the magnetization is abruptly enhanced below 95 K, possibly reflecting an increase of the volume fraction of the ferromagnetic region. The present results support the phase separation scenario that fine ferromagnetic particles embedded in an antiferromagnetic matrix are magnetostatically coupled to each other to form a network of macroscopic sizes.