Non-Griffiths-like clustered phase above the Curie temperature of the doped perovskite cobaltiteLa1−xSrxCoO3

Abstract

The existence of preformed clusters above the Curie temperature of the doped perovskite manganites is well established and, in many cases, conforms to the expectations for a Griffiths phase. We show here that the canonical perovskite cobaltite ͑La 1−x Sr x CoO 3 ͒ also exhibits a clustered state above the Curie point in the ferromagnetic phase. The formation of magnetic clusters at a well-defined temperature ͑T * ͒ is revealed in the small-angle neutron scattering and dc susceptibility. Remarkably, the characteristics of this clustered state appear quite unlike those of a Griffiths phase; the deviation from Curie-Weiss behavior is opposite to expectations and is field independent, while T * does not correspond to the undiluted Curie temperature. These results demonstrate that, although the Griffiths model may apply to many systems with quenched disorder, it is not universally applicable to randomly doped transition metal oxides.

Spray drying: An alternative synthesis method for polycationic oxide compounds

“…The results of magnetic susceptibility (see Fig. 5) obtained here forthe spray-dried sample (T cusp~2 0 K) agree well with the behavior reported by Nam et al [36], whereas other authors [29,37,38] found an irreversibility temperature of ~200 K. The main difference between these literature reports is the duration of the heat treatment: the sample of Nam et al [36] was prepared by solidstate reaction using a 2-month heat treatment. These authors stressed the importance of a homogeneous distribution of strontium cations to prevent any ferromagnetic cluster effects [36].…”

“…These authors stressed the importance of a homogeneous distribution of strontium cations to prevent any ferromagnetic cluster effects [36]. Indeed in the La 1-x Sr x CoO 3 and La 1-x Ba x CoO 3 systems with x below ~0.20, the magnetic behavior is known to be dominated by a frustration state (spin-glass phase), due to the opposition between antiferromagnetic superexchange (Co 3+ -Co 3+ and Co 4+ -Co 4+ interactions) and ferromagnetic double exchange (Co 3+ -Co 4+ interactions) [30,[37][38][39]. In the present work, our sample prepared from a spray-dried precursor displays properties similar to the sample of Nam et al [36] but with a much shorter heat treatment (40 h).…”

Doping Induced Spin State Transition inLaCoO3: Dynamical Mean-Field Study

“…Therefore only small polarons are stable and a substantial change of magnetic properties around x = 0.05 38 suggests that quite different microscopic physics is involved. Other experimental facts pointing against the IS scenario in the metallic phase (x > 0.2) are the lack of substantial magnetoresistance (found in manganites), 8 no Griffiths phase, 39 and observation of positive curvature of inverse susceptibility above T c . 39 The last observation points to increase of the paramagnetic moment with temperature, while in the IS scenario one would expect decrease of IS atoms in magnetically disordered phase.…”

Griffiths-like phase of magnetocaloricR5(SixGe1−x)Pereira1, Morellón2, Magén3 et al. 2010Phys. Rev. B506390View full textAdd to dashboardCite

“…These small clusters give rise to characteristic features that allow the identification of the so-called Griffiths phase, namely, the deviation of the reciprocal susceptibility ͑ −1 ͒ from the Curie-Weiss predictions as the system approaches T C ͑on cooling, from T Ͼ T G ͒, taking the form of an enhanced lowfield susceptibility. 9 Experimental observations of the Griffiths phase were reported much later. A field-induced Griffiths phase was observed in FeCl 2 , manifesting itself as domainlike AFM correlations in the PM state.…”