Random Potential Effect near the Bicritical Region in Perovskite Manganites as Revealed by Comparison with the Ordered Perovskite Analogs

Abstract

The orbital-charge-spin ordering phase diagram for half-doped perovskites Ln(1/2)Ba(1/2)MnO3 (Ln = rare earth) with ordered Ln/Ba cations has been investigated comparatively with that of the Ln/Ba solid-solution analogs. A large modification of the phase diagram is observed upon the A-site disordering near the original bicritical point between the charge-orbital ordering and ferromagnetic metallic phases. The random potential by quenched disorder inherent in the A-site solid solution is found to suppress the respective long-range orders and gives rise to the colossal magnetoresistive state.

Colossal Magnetoresistance and Quenched Disorder in Manganese Oxides

“…In the disordered compounds, charge-order (CO) fluctuations are surprisingly enhanced above T C , 27 and a typical CMR behavior is observed. 25 These results indicate that the competing orders and the quenched disorder play an important role in the CMR phenomena.…”

“…One of the most appealing aspects of these A-site ordered materials is multicritical behavior between the ferromagnetic metallic phase and the charge and orbital ordered insulating phase, as pointed out by Nakajima et al and Akahoshi et al [24][25][26] When the disorder is introduced, the charge/orbital ordered phase becomes unstable and replaced by some glassy phase, and therefore, the multicritical point is strongly suppressed down to much lower temperature. These drastic and asymmetric changes of the phase diagram are depicted in Fig.…”

Magnons in ferromagnetic metallic manganites

“…We should emphasize that besides the doping, the effect of A-site disorder (or chemical disorder) arising from the mismatch between rare-and alkaline-earth-metal ions might induce anomalous spin dynamical behaviour [35][36][37][38]. The A-site disorder is characterized by the standard deviation of the ionic radii:…”

Effect of disorder in an orbitally ordered Jahn-Teller insulator

“…Quenched disorder has been widely acknowledged as a crucial ingredient for the understanding of hole-doped manganites [3,4]. It is the source of a variety of phenomena, both in real materials as well as in model calculations, like the coexistence of metallic and insulating phases [5,6,7,8,9], thermally driven metal to insulator transitions [10,11,12,13], and the suppression of charge order in half-doped systems [14,15].…”