Synthesis, structural, magnetic and phase-transition studies of the ferromagnetic La₂CoMnO₆ double perovskite by symmetry-adapted modes

Abstract

A powdered La2CoMnO6 double perovskite was synthesized by the solid-state reaction method, and its crystal structure was investigated by (mode-crystallography) Rietveld analysis using X-ray and neutron powder diffraction data. La2CoMnO6 material is a monoclinic perovskite at room temperature, adopting the space group P21/n (a(-)a(-)b(+)), , c ≈ 2ap and Z = 2. The P21/n phase can be described effectively by three distortion modes (GM4(+), X3(+), X5(+)) of the Fm3[combining macron]m (a(0)a(0)a(0)) parent phase. The comparative study of the material and those in the Ln2CoMnO6 and Ln2NiMnO6 families has shown a general trend in nearly all the materials, has served to select a common direction in the sub-space spanned by X5(+), tri-linearly coupled to the order parameters of the cubic to monoclinic first order phase transition. This direction has been used to parametrize the refinements and to perform reliable refinements in the high-temperature intermediate distorted trigonal phase, R3[combining macron] (a(-)a(-)a(-)), for which only one effectively acting irrep has been deduced: GM5(+), physically a tilt of the oxygen sharing octahedra of Co and Mn. Its temperature evolution up to the prototype cubic phase has been fitted in the framework of the Landau Theory of Phase Transitions, showing a behavior typical of a tricritical point. The low-temperature neutron powder diffraction data have served to solve the magnetic structure: three indistinguishable ferromagnetic models with the space groups P21/n and P2/n' are proposed.

Structural phase transitions and photoluminescence properties of Eu3+ doped Ca(2−x)BaxLaNbO6 phosphors

“…One can see that while the content of Ba was in the range of 0 ≤ x ≤ 1.2, both the emission intensities of the magneticdipole transition (596 nm) emission spectrum and the electricdipole transition (618 nm) decrease progressively with the increase of temperature as shown in Fig. 26,27 However, the emission intensities of the spectrum turn out to be in the opposite situation when the content of Ba was 1.4 and 2 in Fig.…”

Magnetic and structural phase diagram of the solid solutionLaCoxMn1−xO3

“…19,20 The coexistence of these phases is almost unavoidable, though the fraction of each can be controlled by the preparation method followed. 19,21 It is therefore perhaps unsurprising that a range of magnetic ground-states has been proposed, from long range ferromagnetic order, 22 to cluster-glass models, 23 and even superparamagnetism. 24 For x = 0.8, a similar, though less pronounced, non-uniform magnetic behaviour was observed and was attributed to the existence of small ferromagnetic clusters in a disordered matrix.…”

Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1−xMgxTeO6(x = 0.1, 0.2 and 0.5)

“…We performed all the structural analyses using the modecrystallography approach, [13][14][15][16][17]40 which is a perfect tool to analyze and study phase transitions, one of the main goals of the manuscript. The approach is based on the symmetry of a prototype phase, and its irreps, and on the natural breaking of that symmetry.…”