Neutron-powder-diffraction study of the magnetic and structural properties of Pr_0.6(Ca_1-xSr_x)_0.4MnO₃ (0<~x<~1)

We present the results of a neutron-powder-diffraction study in which we have examined the magnetic and structural properties of Pr_0.6(Ca_1-xSr_x)_0.4MnO₃ (0<~x<~1) as a function of doping concentration x and temperature. For x<~0.15 charge ordering and a Jahn-Teller distortion below 250 K are evident from rapid changes in the lattice parameters and bond lengths as a function of temperature and a transition from a high-temperature orthorhombic to a low-temperature monoclinic structure. For x=0.0 the system orders antiferromagnetically at T_N=170K. At low temperature the system has a canted CE structure. As the temperature approaches T_N there is a transition to a collinear magnetic arrangement. For Sr doping of up to x=0.15 the magnetic transition temperature remains almost constant but the magnetic arrangement now has a ferromagnetic component which persists up to T_N. For x>0.15 the charge ordering is removed and the lattice parameters show a more normal temperature dependence. The materials are now simple ferromagnets and the ferromagnetic transition temperature T_C increases rapidly with x.