Phase separation as origin of the magnetic anomalies in La0.85Sr0.15CoO3

Abstract

The dependence of the ac-magnetic susceptibility of La0.85Sr0.15CoO3 on the annealing temperature used during synthesis is addressed. Such dependence has been previously attributed to compositional inhomogeneities. Nevertheless, the presence of distinct phases with different chemical compositions is excluded after explorations by several techniques. Instead it is proposed that an electronic phase separation takes place in the material, whose state is changed after charge-carrier redistributions due to the thermal history of the samples, analogously to parent manganese-based perovskites.

The role of iron in the formation of the magnetic structure and related properties of La0.8Sr0.2Co1−xFexO3 (x=0.15, 0.2, 0.3)

“…The same kind of phase separation also occurs for 0.05pyp0.18, in which case La 1Ày Sr y CoO 3 is semiconducting and displays a spin-glass-like magnetic ground state [10,11]. Nanometer scale phase separation of La 1Ày Sr y CoO 3 clearly visualized itself in high-resolution electron microscopy [5] and small-angle neutron scattering [12] measurements, while the existence of nanosized ferromagnetic clusters in La 1Ày Sr y CoO 3 with yo0.2 was also evidenced by magnetic susceptibility measurements that reflected superparamagnetic behavior [3].…”

“…[1]) as well as because they present a model system for intrinsic electronic phase separation and associated magnetic phenomena [2][3][4][5]. According to the phase diagram of La 1-y Sr y CoO 3 [3,6,7] Sr doping gradually turns the insulating nonmagnetic ground state of the parent compound LaCoO 3 -being in the focus of scientific interest also on its own ground [8,9]-into a ferromagnetic metal (FM) state with a Curie temperature of $250 K for y ¼ 0.5 [7].…”

Magnetization reversal and nanoscopic magnetic-phase separation inLa1−xSrxCoO3

“…This stems from two important features of perovskite oxides; (i) they possess an additional degree of freedom associated with the Co ion spin state (which cannot be accessed in manganites and cuprates), and (ii) they exhibit a particularly clear and simple form of magnetic phase separation. 12,13,25,26 It has been recently proven by TEM, 12,13 SANS, 26 and NMR, 27,28 that at low doping (x < 0.18) the canonical doped perovskite cobaltite La 1-x Sr x CoO 3 (LSCO) phase separates into ferromagnetic (FM) metallic clusters embedded in a non-FM insulating matrix. As x increases these clusters become more populous leading to a simple coalescence into a long-range ordered FM network and a coincident percolation transition to a metallic state at x ≥ 0.18.…”

“…23 It is important to note that this phase separation is also the subject of intense investigation from the theoretical point of view and that its existence can be reproduced with relatively simple models. 5,7,24 Doped perovskite cobaltites, which have been the subject of far less investigation than their extensively studied manganite counterparts, 12,13,20,25,26 offer some unique opportunities for fundamental investigations of correlated electron oxides. This stems from two important features of perovskite oxides; (i) they possess an additional degree of freedom associated with the Co ion spin state (which cannot be accessed in manganites and cuprates), and (ii) they exhibit a particularly clear and simple form of magnetic phase separation.…”

“…These techniques include direct spatial probes [e.g. scanning tunneling microcopy (STM) and spectroscopy (STS), [8][9][10][11] transmission electron microscopy (TEM), 12,13 and magneto-optical imaging 14 ], diffraction and scattering techniques [e.g. neutron diffraction and small-angle neutron scattering (SANS) 12,[15][16][17][18][19][20] ], resonance techniques [e.g.…”