Structure, spin glass, and spin state in perovskite GdCo/sub 1-x/Mn/sub x/O/sub 3/ (x /spl les/ 0.5)
Perovskite GdCo/sub 1-x/Mn/sub x/O/sub 3/ (x=0.2,0.3,0.4,0.5) compounds have been prepared by solid-state reaction. Structures were characterized using X-ray diffraction and Rietveld Refinement method. The compounds crystallized in orthorhombic with Plmn space group. Crystal lattices decreased with the increase of Mn doping level. DC magnetization and ac susceptibility were studied over a wide temperature range and different frequencies. A typical spin glass state was observed in all samples around the same temperature of 122 K where the compounds turned from paramagnetic to ferromagnetic states. For x<0.5, secondary transitions were observed both in dc and ac measurement which were independent of frequency but depended on doping level. The valences of Co or Mn with possible spin states were estimated.
Metamagnetism in the perovskite compound Gd2CoMnO6
Abstract The compound Gd2CoMnO6 crystallizes with the orthorhombic perovskite structure and is isomorphous with GdFeO3. A crystal structure refinement shows that the Mn3+-O2−-Mn3+ bond angles are ∼ 145° and that the distortion from cubic symmetry is considerable. A spontaneous moment of 5 e.m.u./g develops below 115°K due to the exchange interactions between near neighbouring Mn3+ ions. Below 115°K a field induced metamagnetic transition to a state with a moment of 20 e.m.u./g is also observed and this transition is depressed in temperature by 1°c for 360 oe applied field. The metamagnetism is accounted for on the basis of a transition between an uncompensated anti-ferromagnetic and a ferromagnetic state which is observed in Gd2CoMnO6 due to a change in sign of the Mn3+-O2−-Mn3+ exchange interaction originating from Jahn-Teller electronic ordering in Mn3+ ions. This ordering is favoured at low temperatures and introduces a negative contribution to the exchange interaction.
Effect of the Cation Size on the Physical Properties in Perovskite Manganite Oxides
We studied the structural, magnetic and electrical properties as a function of the average size of the A cation site, (r A ), in the perovskite manganite (Pr 1-y M y ) 0.7 Sr 0.3 MnO 3 oxides with y = 0, 0.1 and M = Sm, Bi. X-ray diffraction investigations show that our synthesized samples crystallize in the orthorhombic symmetry with Pnma space group. Magnetic measurements versus temperature in an applied magnetic field of 500 Oe show that all our samples exhibit a paramagnetic to ferromagnetic transition when temperature decreases. The Curie temperature T C decreases from 265 to 215 K when (r A ) varies from 1.2183 to 1.2150 A. Electrical measurements show that all samples exhibit a semiconducting to metallic transition with decreasing temperature. The electrical transition temperature decreases with decreasing (r A ).