Charge ordering in the rare-earth manganates: the origin of the extraordinary sensitivity to the average radius of the A-site cations,

Abstract

The charge ordering in , which occurs on cooling the ferromagnetic metallic ground state, is readily destroyed on application of a magnetic field of 6 T. For , for which the ground state is charge ordered, on the other hand, magnetic fields have no effect on the charge ordering. In order to understand such a marked difference in charge-ordering behaviour of the manganates, we have investigated the structure as well as the electrical and magnetic properties of compositions (Ln = Nd, Sm, Gd and Dy) wherein varies over the range 1.17-1.13 Å. The lattice distortion index, D, and charge-ordering transition temperature, , for the manganates increase with the decreasing . The charge-ordered state is transformed to a metallic state on applying a magnetic field of 6 T in the case of , but this is not the case with the analogous Sm, Gd and Dy manganates with less than 1.17 Å. In order to explain this behaviour, we have examined the -dependence of the Mn-O-Mn bond angle, the average Mn-O distance and the apparent one-electron bandwidth, obtained from these structural parameters. It is suggested that the extraordinary sensitivity of the charge ordering to arises from factors other than those based on the Mn-O-Mn bond angle and average Mn-O distances alone. It is possible that the competition between the covalent mixing of the oxygen orbital with the A-site and B-site cation orbitals plays a crucial role. Strain effects due to size mismatch between A-site cations could also cause considerable changes in .

Thickness dependence of the stability of the charge-ordered state inPr0.5Ca0.5MnOPrellier1, Simon2, Haghiri‐Gosnet3 et al. 2000Phys. Rev. B889901View full textAdd to dashboardCite

“…In the mean time, the critical field required to melt the CO state is also decreasing. This behavior is similar to that observed for bulk materials RE 1−x Ca x MnO 3 , whose CO state is destabilized when the tolerance factor is getting close to one (or the size of the A-site cation is increasing) 13,21 . In return, the present evolution of the magnetotransport properties cannot be directly compared to that of the bulk compound Pr 0.5 Ca 0.5 MnO 3 , due to the different nature of the cell distortion imposed by the substrate.…”

Effect of size reduction on the ferromagnetism of the manganite La1−xCaxMnO3(x=0.33)

“…We find that there is a likely enhancement of W on size reduction. An estimate of the bandwidth W (in the double exchange model) can be made from the relation [33,34] …”

Magnetic Properties of LnMnO3 (Ln=Ho, Er, Tm, Yb, and Lu)

“…Ca-substituted compounds Ln 0.5 Ca 0.5 MnO 3 , where the nominal valence of the Mn ions is 3.5+, were also prepared for comparison; their magnetic properties are briefly considered as well. Magnetic properties for such systems have been reported for Y 0.5 Ca 0.5 MnO 3 (11,12) and Y 0.7 Ca 0.3 MnO 3 (13), exhibiting charge order below 260 K and spin-glass behavior below 30 K, respectively.…”