Glassy behaviour of the ferromagnetic and the non-magnetic insulating states of the rare earth manganatesLn0.7Ba0.3MnO3 (Ln = Nd or Gd)

Abstract

While La0.7Ba0.3MnO3 is a ferromagneticmetal (TC = 340 K)withlong-range ordering, Nd0.7Ba0.3MnO3 shows a transition around 150 K with a small increase in magnetization, but remains an insulator at alltemperatures. Gd0.7Ba0.3MnO3 is non-magnetic and insulating at all temperatures. Low field dc magnetization and acsusceptibility measurements reveal the presence of a transition at around 150 K inNd0.7Ba0.3MnO3,and a complex behaviour with different ordering/freezing transitions at 62, 46 and 36 K in the caseof Gd0.7Ba0.3MnO3, the last one being more prominent. The nature of the field dependence of the magnetization,combined with the slow magnetic relaxation, ageing and memory effects, suggests thatNd0.7Ba0.3MnO3 is a cluster glass below 150 K, a situation similar to that found forLa1−xSrxCoO3.Gd0.7Ba0.3MnO3, however, shows non-equilibrium dynamics characteristic of spin glasses,below 36 K. The difference in nature of the glassy behaviour betweenGd0.7Ba0.3MnO3 and Nd0.7Ba0.3MnO3 probably arises because of the larger disorder arising from the mismatchbetween the sizes of the A-site cations in the former. Our results onNd0.7Ba0.3MnO3 and Gd0.7Ba0.3MnO3 suggest that the magnetic insulating states often reported for rare earth manganates of the typeLn1−xAxMnO3 (Ln = rare earth, A = alkaline earth) are likely to be associated with glassy magnetic behaviour.