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Résumé |
Depending on the size of the ionic radii of the R3+ and A2+ ions in the (R1-x Ax¬)n+1 Mnn O3n+1 manganites (R is a rare earth and A is an alkaline earth element), the ferromagnetic metallic phase, or the charge- and orbital-ordered (CO-OO) can be stabilized. It was shown in the perovskite case (n=inf., R 1-x Ax MnO3 ) that in the presence of the disorder introduced by the solid solution of the R3+ and A2+ ions, the long-range CO-OO phase collapses in a first-order manner, and only a nanometer-sized CO-OO correlation, and associated spin glass state
remain. This “CE-glass“ state appears to contain all the building blocks for the colossal magnetoresistance (CMR) phenomenon. We have here investigated in detail the effect of the quenched disorder in half-doped perovskite and two-dimensional single-layered manganites (n=1, R0.5 A1.5 MnO4 ). The appearance of the nanoscale phase separation, or CE-glass, in the single-layered manganites is investigated as a function of the bandwidth and amount of disorder. The dynamical properties of the associated spin glass state, which shows either archetypal or anisotropic (XY) properties, are discussed and compared to those of the magnetically frustrated and two-dimensional configurations of the hole underdoped crystals.
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