Structural tuning of magnetism in the orthorhombic perovskite Nd 1 − x Y x MnO 3 : Evidence for magnetic phase separation

We report on the magnetic and structural properties of the perovskite solid solution ${\text{Nd}}_{1\ensuremath{-}x}{\text{Y}}_{x}{\text{MnO}}_{3}$, using magnetization and neutron powder-diffraction measurements. The orthorhombic perovskite structure $(Pbnm)$ is obtained over the composition range of $0\ensuremath{\le}x\ensuremath{\le}0.6$. The Mn-O-Mn bond angles and the N\'eel temperature ${T}_{N}$ decrease with increasing $x$ and track closely similar behavior established for the general series of manganites $R{\text{MnO}}_{3}$ ($R=\text{rare}$ earth). For lower doped samples, the antiferromagnetic $A$-type Mn order is stable, while for higher doping the diffraction data can be modeled using an incommensurate spin-density-wave (SDW) model. In both cases, we find that Mn spins are aligned along the $b$ axis. For intermediate compositions $0.4\ensuremath{\le}xl0.55$, we find a coexistence of $A$-type and SDW magnetic order. On symmetry grounds, we argue that these two magnetic phases cannot occupy the same volume but rather this coexistence region is indicative of a notable magnetic phase separation.