Orbital order-disorder transition inLa1−xNdxMnO3(

Abstract

The nature of orbital order-disorder transition has been studied in

Effect of disorder in an orbitally ordered Jahn-Teller insulator

“…The observed qualitative difference between the moderate and strong coupling systems raise the possibility, that the orbital order to disorder transitions in the two cases may be qualitatively different. Experimentally it is known that the transition in LaMnO 3 is first order in nature and becomes second order for PrMnO 3 and NdMnO 3 , which are smaller bandwidth materials [22,40,41]. Although the origin for a first order nature of the transition in LaMnO 3 is suggested to be anharmonic coupling between JT distortions and volume strain [42], the bandwidth variation may also be playing a role.…”

“…In real systems however, it is difficult to isolate the individual effect of quenched disorder. Isoelectronic rare-earth substitution series such as in La 1−y Nd y MnO 3 , involve a simultaneous change of effective bandwidth and disorder [22]. The increase in T OO upon increasing y in this series is understood mainly from the increase in the average ionic radius but changes in y are necessarily accompanied by variations in disorder.…”

“…The combined effect of disorder and hole doping has been briefly reported elsewhere [9]. A model system, which includes disorder remaining at x = 0 is experimentally relevant for systems with isoelectronic substitutions such as RE 1−y RE ′ y MnO 3 [22]. The manganites are complex materials involving the the interplay of spin, orbital, lattice, and charge degrees of freedom.…”

Manganites - Structural Aspects

“…For compounds with y = 0.75 neutron diffraction data for the sample with the 18 O isotope give an additional reflection of the magnetic origin correlated with the propagation vector k = (1/2, 0, 1/2) which corresponds to an antiferromagnetic structure. These data indicate a noncollinear structure for the 16 (Fig. 1).…”

“…In the (La 1−y Pr y ) 0.7 Ca 0.3 MnO 3 compounds substitution of the 16 O isotope by 18 O caused the change of the transport properties from metal to insulator [14]. For compounds with y = 0.75 neutron diffraction data for the sample with the 18 O isotope give an additional reflection of the magnetic origin correlated with the propagation vector k = (1/2, 0, 1/2) which corresponds to an antiferromagnetic structure.…”