Structural, magnetic, and transport properties of the single-layered perovskitesLa2−xSrxCoO4

Abstract

The layered cobaltites La 2−x Sr x CoO 4 have been complexly studied over the range of mixed Co 3+/4+ valency and their properties discussed in comparison with cubic perovskites La 1−x Sr x CoO 3 . The sample x = 1.0 exhibits a paramagnetic ground state based on the intermediate spin state of Co 3+ and undergoes a broad resistivity transition at 400-900 K, associated with diffusive changes of magnetic susceptibility and volume expansion. The Co 4+ doping in samples with x Ͼ 1 induces gradually ferromagnetism and leads to a dramatic decrease of resistivity and thermopower, though the metallicity is not achieved. The neutron diffraction on the limit composition x = 1.4 suggests that the long-range ordered ferromagnetic regions coexist with paramagnetic ones, and their amount changes little with an application of high pressures up to 4.3 GPa.

Single Crystal Growth of Pure Co3+ Oxidation State Material LaSrCoO4

“…T f can be suppressed with increasing magnetic field within the range of 0.01 T to 1 T from about 7.1 K to 4.0 K. Such a behavior might be indicative of a ferromagnetic or a spin glass transition. Furthermore, in our single crystals, any intergrowths of other Ruddlesden-Popper phases which are known to exhibit ferro-/ferri-magnetic transitions around 250 K [11,13] are absent in our single crystals, as is shown in the inset of Figure 3a. All of these measurements indicate the high quality of our crystals.…”

“…A study on polycrystals reveals a spin glass transition below about 10 K [11]. Other studies on single-and polycrystalline samples indicate a paramagnetic state [12,13]. Note that there is no characterization of the Co valence state in these compounds.…”

“…Moreover, small amounts of other Ruddlesden-Popper phases (e.g., double-layer perovskite phases) might appear as intergrowths which dominate the magnetic properties of the studied samples. Single crystal growth of LaSrCoO 4 is reported in References [12,13], but the growing speed is rather fast and only small pieces of single crystalline samples were obtained. The lack of large impurity-free single crystals renders the investigation of LaSrCoO 4 by means of inelastic neutron scattering difficult.…”

Metal-insulator transition in Sr2−xLaxCoO4driven by

“…5 Upon La doping (x = 0.5), Sr 1.5 La 0.5 CoO 4 turns semiconducting but remains FM. 6,7 With La doping up to x = 1, SrLaCoO 4 becomes a paramagnetic insulator. [6][7][8] It is well known that cobaltates often have a spin-state issue.…”

Structural and magnetic properties of the cobaltate series (BaSr)4−xLa2xCo

“…A signature characteristic of cobalt oxides that distinguishes them from the other transition metal oxides is that Co ions are all susceptible to having multiple valence and/or spin states. [1][2][3][4][5][6][7] The different electronic configurations can appear as a result of the interplay between the crystal field, caused by the local atomic environment, and the interatomic exchange interaction. Perhaps the most extensively studied cobaltates in which the polyvalency and multi-spin states come to play to produce complex phase diagrams have been La 2−x Sr x CoO 4 , 1-4 and La 1−x Sr x CoO 3 , 5-8 .…”