Pseudo-1D magnetic order and fluctuation behavior of 3d-dopants in superconducting YBa₂Cu₃₋ₓFeₓO₇₊[sub δ] by Weimin Peng

Includes bibliographical references (pages [45]-50)It is shown that Fe substituents in the Cul site of YBa₂Cu₃₋ₓFeₓO₇₊[sub δ] (x =0.15, 0.30) magnetically order into quasi- ID chains with strong intrachain but weak interchain coupling. The strong fluctuation behavior expected in low dimensional systems above and below T[sub N] is observed via characteristic relaxation in the Mossbauer line width near T[sub N]. The temperature dependence of the magnetic subspectra representing Fe ions with various local oxygen environments are in agreement with a 2D-Ising model, with a ratio of the anisotropic exchange between the two directions of the order of 0.5-1 . 0 (10⁻³). The concentration dependence of the relative occurrence of various magnitudes of the local dopant magnetization is related to a short range chemical order which determines the magnetic chain size and defines the correlation lengths. Evidence is given that the presence of rare earth magnetic moments in the Y-site affects the character of the magnetic interaction in the Cul-site.M.S. (Master of Science