Spontaneous cationic ordering in chemical-solution-grown La2CoMnO6 double perovskite thin films

Abstract

Double perovskite oxides are of interest because of their electric, magnetic, and elastic properties; however, these properties are strongly dependent on the ordered arrangement of cations in the double perovskite structure. Therefore, many efforts have been made to improve the level of cationic ordering to obtain optimal properties while suppressing antisite defect formation. Here, epitaxial double perovskite La 2 CoMnO 6 thin films were grown on top of (001)-STO oriented substrates by a polymer-assisted deposition chemical solution approach. Confirmation of the achievement of full Co/Mn cationic ordering was found by scanning transmission electron microscopy (STEM) measurements; EELS maps indicated the ordered occupancy of B-B′ sites by Co/Mn cations. As a result, optimal magnetic properties (Msat ≈ 6 µ B /f.u. and Tc ≈ 230 K) are obtained. We show that the slow growth rates that occur close to thermodynamic equilibrium conditions in chemical solution methods represent an advantageous alternative to physical deposition methods for the preparation of oxide thin films in which complex cationic ordering is involved.

Aqueous Chemical Solution Deposition of Functional Double Perovskite Epitaxial Thin Films

“…An out-of-plane lattice parameter c = 3.872 is estimated fromt he high-resolutionX -ray diffraction pattern of the (0 02)d iffraction peak (see Figure 3(c)). These measurements performed in new samples confirmo ur previous results on the LCMO/STO system [22] andm ake evident the high stability of the precursor solutions and the reproducibilityo ft he samples. On the other hand, LCMO films grown on LAO were fully relaxed,a nd the in-plane parameter estimatedf rom the reciprocal space map is about a = 3.89 ,F igure 3 (b).…”

“…Recently,w eh ave shown that the particular growth conditions of PAD( very slow rate and close to thermodynamic equilibrium conditions) are prone to promote high quality,a sw ell as B-site ordered, LCMO/STO epitaxial thin films. [22] Accordingly,t he magnetic properties extracted from measurements in optimized LCMO/ STO new samples (growth temperature 900 8Cf or 60 min with an oxygen flow of 0.3 lmin À1 )c onfirmt he previousr esults obtained in ref. [22],a nd exhibit aC urie temperature of T C = 230 K( see Figure 5(a)).…”

“…[20a, 21] Thus, crystallization of the oxide takes place near the decomposition temperature of the polymer and nitrates, that is, close to thermodynamic equilibrium conditions;a nd it has been proposed that these particular growth conditions of PADa re much more favorable for attaining spontaneous B-site cationic ordering. [22] Figure 2s hows atomic force microscopy topography images in tapping mode of representative LCMO and LNMO films grown on top of STO andL AO substrates (film thickness d % 25 nm). Samples were grown at 900 8C, with heating and cooling ramps of 3degrees min À1 ,d well time 60 min, and oxygen flow 0.3 Lmin À1 .T opography showsahigh-quality flat surfacew ith root-mean-square (rms) values of surfacer oughness below 2nmi na ll cases.…”

“…Samples with thicknesses below 10 nm clearly show the terrace-like morphology imposed by the conformal growth on top of the substrate steps. [22] Sample uniformity across the whole surface area has been demonstrated by field-emission scanninge lectron microscopy,v isualizing secondary electron images (information on topography) as well as backscattered electroni mages (sensitive to differences in composition).…”

“…In this context,t he above-mentioned specificities of PADh ave provent ob ev ery beneficial fort he growth of complexo xide layers [21] and, recently,w eh ave demonstrated the PADg rowth of B-site orderedL a 2 CoMnO 6 /SrTiO 3 double perovskite epitaxialt hin films, with perfectc rystallinity and ah igh degree of B-site cationic ordering. [22] In the present work, we report the epitaxialg rowth of La 2 CoMnO 6 (LCMO) and La 2 NiMnO 6 (LNMO) compounds on (0 01)-SrTiO 3 (STO) and (0 01)-LaAlO 3 (LAO) substrates by the PADt echnique. We have investigated the influence of the substrate, on the structure and magnetic properties of the films.…”