Electron spin resonance and neutron diffraction studies of Nd0.5-0xPrxSr0.5MnO3 (x=0.125, 0.25)

Effects of Pr substitution on the magnetic properties of perovskite manganite Nd 0.5 Sr 0.5 MnO 3 have been investigated by measurements of electron spin resonance, magnetization, and powder neutron diffraction. These experiments evidence a complex phase-segregated state at low temperatures and coexistence of different ferromagnetic (FM) and antiferromagnetic (AFM) arrangements. Four temperature regions are distinguished, similar for both studied samples Nd 0.5-x Pr x Sr 0.5 MnO 3 (x = 0.125, 0.25). Around the room temperature and above there is a region of a single orthorhombic perovskite Ibmm phase of paramagnetic (PM) state, where the first signatures for FM clusters can be indicated in the electron spin resonance spectra below ∼1.1 T C (T C = 260 K). Between T C and T C2 (230 K for x = 0.25), a new tetragonal perovskite I4/mcm phase of FM long range order is formed at the expense of the PM orthorhombic phase. Below T C2 , the FM order is established in both crystallographic phases, and the amount of the tetragonal phase for x = 0.25 achieves a maximum close to 45% of the sample. Finally, below ∼160 K, strongly distorted perovskite domains with the CE and A-type kinds of AFM order (T N = 150 K for x = 0.25) are segregated while the orthorhombic FM phase quickly vanishes. At the lowest temperatures, the two structurally distorted AFM domains make up 72% of the x = 0.25 sample, and the remaining 28% belongs to the tetragonal FM domains.