A critical re-examination and a revised phase diagram ofLa1 − xSrxCoO3

Abstract

We report the results of a comprehensive study on dc magnetization,ac susceptibility, and the magnetotransport properties of theLa1 − xSrxCoO3(0 ≤ x ≤ 0.5) system. At higherSr doping (x ≥ 0.18), the system exhibits Brillouin-like field cooled magnetization(MFC). However, forx < 0.18, the system exhibitsa kink in the MFC, a peak at the intermediate field in the thermoremnant magnetization and a non-saturating tendency inthe M–H plot thatall point towards the characteristic of spin glass behavior. More interestingly, dc magnetization studiesfor x < 0.18 do not suggest the existence of ferromagnetic correlation that can give rise toan irreversible line in the spin glass regime. The ac susceptibility study forx > 0.2 exhibits apparently no frequency dependent peak shift around theferromagnetic transition region. However, a feeble signature of glassinessis verified by studying the frequency dependent shoulder position inχ′′(T) and the memory effect below the Curie temperature. But, forx < 0.18, the ac susceptibility study exhibits a considerable frequency dependent peak shift,time dependent memory effect, and the characteristic spin relaxation time scaleτo ∼ 10 − 13 s. The reciprocal susceptibility versus temperature plot adheres to Curie–Weiss behavior and doesnot provide any signature of preformed ferromagnetic clusters well above the Curie temperature.The magnetotransport study reveals a cross over from metallic to semiconducting-like behavior forx ≤ 0.18. On the semiconducting side, the system exhibits a large value of magnetoresistance (upto75%) towards low temperature and it is strongly connected to the spin dependent part ofthe random potential distribution in the spin glass phase. Based on the above observations,we have reconstructed a new magnetic phase diagram and characterized each phase withassociated properties.