Long-scale phase separation versus homogeneous magnetic state in (La1-yPry)0.7Ca0.3MnO3: A neutron diffraction study

The magnetic structure of the series (La1-yPry)0.7Ca0.3MnO3 for y from 0.5 to 1.0 has been studied by neutron powder diffraction in the temperature range from 10 to 293 K and in external magnetic fields up to 4 T. The phase diagram has a border region of concentrations 0.6≤y≤0.8 separating the homogeneous ferromagnetic (FM) metallic and canted antiferromagnetic (AFM) insulating states. In this region the low-temperature magnetic state is macroscopically (>103 A) separated into AFM and FM phases. The FM phase has a small noncollinearity, presumably due to interfaces to the AFM phase. The macroscopical clusters can be induced by disorder on the carrier's hopping amplitude caused by natural dispersion of the A cation radius near the metal-insulator transition around y=0.7. For the concentrations y≥0.9 the long-range ordered magnetic state is homogeneous with a canted AFM structure. The total long-range ordered magnetic moment of the Mn ion shows a steplike decrease from μMn=3.4μB to 2.5μB as a function of Pr concentration at the transition to a homogeneous canted antiferromagnetic (CAF) state. The spatial inhomogeneities can still be present for y≥0.9, according to the reduced μMn value, but the Mn spins between the homogeneously CAF-ordered moments have to be either short-range ordered or paramagnetic. In addition, a ferromagnetic contribution of the Pr moments parallel to the ferromagnetic component of Mn moments is found for y>0.6. The moment of Pr scales with the ferromagnetic Mn moment rather than with the Pr concentration and thus presumably induced by Mn