Long-scale phase separation versus homogeneous magnetic state in (La1-yPry)(0.7)Ca0.3MnO3: A neutron diffraction study - art. no. 024420

The magnetic structure of the series (La1-y,Pr-y)(0.7)Ca0.3MnO3 for y from 0.5 to 1.0 has been studied by neutron powder diffraction in the temperatur e range from 10 to 293 K and in external magnetic fields up to 3 T. The pha se diagram has a border region of concentrations 0.6 less than or equal toy less than or equal to0.8 separating the homogeneous ferromagnetic (FM) met allic and canted antiferromagnetic (AFM) insulating states. In this region the low-temperature magnetic state is macroscopically (>10(3) Angstrom) sep arated into AFM and FM phases. The FM phase has a small noncollinearity, pr esumably due to interfaces to the AFM phase. The macroscopical clusters can be induced by disorder on the carrier's hopping amplitude caused by natura l dispersion of the A cation radius near the metal-insulator transition aro und y = 0.7. For the concentrations y greater than or equal to0.9 the long- range ordered magnetic state is homogeneous with a canted AFM structure. Th e total long-range ordered magnetic moment of the Mn ion shows a steplike d ecrease from mu (Mn)=3.4 mu (B) to 2.5 mu (B) as a function of Pr concentra tion at the transition to a homogeneous canted antiferromagnetic (CAF) stat e. The spatial inhomogeneities can still be present for y greater than or e qual to0.9, according to the reduced mu (Mn) value, but the Mn spins betwee n the homogeneously CAF-ordered moments have to be either short-range order ed or paramagnetic. In addition, a ferromagnetic contribution of the Pr mom ents 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.