Early and recent studies have explained this dichotomy using the charge and orbital ordering model (CO-OO) adopted, especially when x is equal to a simple fraction, e.g., x = n/( n + 1) with n = 1, 2, and 3. Our results may aid attempts to understand more deeply phenomena related to spin, charge, and orbital ordering, as well as colossal magnetoresistance and symmetry breaking and emergent order in quantum states.Īn important unresolved issue in understanding the physics of La 1− xCa xMnO 3 relates to the physical mechanism responsible for the change in the ground state from ferromagnetic metallic for 0.23 < x < 0.5 to antiferromagnetic insulating for 0.5 < x ≤ 1 (for reviews see refs. At the base temperature of 5 K, the modulation vector of the superstructure τ = is parallel to the a-axis, with τ a varying linearly with x, as τ a ≈ 1 − x. The experimental results reveal that all compounds undergo a structural transition at T < T CO( x) ≈ 200 − 220 K with the concomitant emergence of superlattice Bragg peaks, which can be indexed assuming a superstructure with a modulation propagation vector, τ. Here we study the crystal structure in a series of compounds with 0.5 < x ≤ 0.6 using ultrahigh-resolution synchrotron X-ray diffraction. To fully understand the crystal and electronic structures of these materials, it is important to study compounds with doping levels in the range of 0.5 < x < 2/3. In the past, only compounds with x = 1/2, 2/3 and 3/4 and an insulating ground/antiferromagnetic state have been studied. In the model manganese perovskites La 1− xCa xMnO 3, several important phenomena have been observed, including ferromagnetic metallic/insulating states, colossal magnetoresistance effects, and charge- and orbital-ordered states.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |