A systematic study of four series of electron-doped rare earthmanganates, LnxCa1−xMnO3 (Ln = La, Nd, Gd and Y) overthe x = 0.02– 0.25composition range

Abstract

Electrical and magnetic properties of four series of manganatesLnxCa1−xMnO3(Ln = La,Nd, Gd and Y) have been studied in the electron-doped regime (x = 0.02 – 0.25)in order to investigate the various inter-dependent phenomena such asferromagnetism, phase separation and charge ordering. The general behaviour ofall four series of manganates is similar, with some of the properties showing adependence on the average radius of the A-site cations, ⟨rA ⟩ and cationsize disorder. Thus, all the compositions show an increase in magnetization at 100–120 K(TM) forx < xmax,the magnetization increasing with increasingx. The valueof xmaxincreases with decreasing ⟨rA ⟩,probably due to the increased phase separation induced by site disorder.This is also reflected in the larger width of the hysteresis loops atT < TM for small x or ⟨rA ⟩.In this regime, the electrical resistivity decreases with increasingx, but remains low andnearly constant, T > TM.The percolative nature of the conduction mechanism atT < TMis substantiated by the fit of the conductivity data tothe scaling law, σ ∝ |xc − x|p, wherep is in the 2–4 range.When x > xmax,the materials become antiferromagnetic (AFM) and charge-ordered at a temperatureTCA,accompanied by a marked increase in resistivity. The value ofTCAincreases with increasing ⟨rA ⟩ andx (up tox = 0.3). Thus,all four series of manganates are characterized by a phase-separated regime betweenx = 0.02and 0.1–0.15 and an AFM charge-ordered regime at x > 0.1– 0.15.