The low-temperature and high-magnetic field (2K, 8T) powder x-ray diffraction (LTHM-XRD) measurements have been carried out at different temperatures (T) and magnetic fields (H) to investigate the structural phase diagram for phase separated La0.175P
r0.45Ca0.375MnO3 (LPCMO) manganite. The antiferromagnetic (AFM) P21/m insulating phase undergoes field induced transformation to ferromagnetic (FM) Pnma metallic ground state below its AFM ordering temperature (220K) in zero-field cooling (ZFC) from room temperature. At temperature greater than 25K, the field induced FM Pnma phase remained irreversible even after complete removal of field. However, for T ( 39-65K), the field induced transformation is partially reversible. This behaviour has been attributed to magnetic field induced devitrification of the glass-like arrested AFM P21/m phase to FM Pnma equilibrium phase. The devitrified FM Pnma phase starts transforming back to AFM P21/m phase around ~39K on heating the sample under zero field. Our results corroborate the evidence of strong magneto-structural coupling in this system. An H-T phase-diagram has been constructed based on LTHM-XTD data, which resembles with the one made from magnetic measurements. These results have been explained on the basis of kinetic arrest of first order phase transition and field induced devitrification of the arrested phase.
Low as well as high-temperature electron and x-ray diffraction studies have been carried out on a rare-earth free B-site disordered electron-doped manganite SrMn0.875.Mo0.125O3-{delta} in the temperature range of 83K to 637K. These studies reveal the
occurrence of strong charge ordering (CO) at room temperature in a pseudo tetragonally distorted perovskite phase with space-group Pmmm. Non integral modulation vector of 8.95 times along [-110] indicates a charge density wave type modulation. The CO phase with basic perovskite structure Pmmm transforms to a charge disorder cubic phase through a first order phase transition at 355K. Supporting temperature dependent measurements of resistance and magnetization show a metal-insulator and antiferromagnetic transitions across 355K with a wide hysterisis ranging from 150K to 365K. The occurrence of pseudo tetragonality of the basic perovskite lattice with c/a < 1 together with charge-ordered regions with 2-dimensional modulation have been analyzed as the coexistence of two CO phases with 3dx2/3dy2 type and 3dx2-y2 type orbital ordering.
We report the existence of ferromagnetic correlations (FMC) in paramagnetic (PM) matrix of cubic La1-xSrxMnO3-{delta} (x = 0.80, 0.85) well above its coupled structural, magnetic and electronic phase transitions. The dc-magnetization vs temperature [
M(T)] behaviour under different magnetic fields (from 100 Oe to 70 kOe) shows the presence of short range magnetic correlations up to (TFMC ~) 365 K, far above the antiferromagnetic ordering temperatures (TN =) 260 K and 238 K for x=0.80 and 0.85, respectively. More importantly the observed short-range FMC survive even up to 70 kOe, which indicates their robust nature. The temperature region between TN to TFMC is dominated by the presence of correlated ferromagnetic (FM) entities within the PM matrix and stabilized due to A-site chemical disorder. Our results further illustrate that for the studied compositions, the oxygen off-stoichiometry does not have any significant effect on the nature and strength of these FM entities; however, FM interactions increase in the oxygen deficient samples. These compositions are the unique examples, where the presence of FMC is observed in an undistorted basic cubic perovskite lattice well above TN and therefore are novel to understand the physics behind the colossal magneto-resistance effect.
