Synthesis and magnetic properties of novel Ln{sub 2-x}M{sub x}CuO{sub 4+y} compositions (Ln = La, Pr, Nd, Sm, Eu, Gd; M = Ca, Sr, Ba; 0 {le} x {le} 0.2; {minus}0.5 {le} y {le} 0.5)
Ln{sub 2}CuO{sub 4} undergo transitions to reduced Ln{sub 2}CuO{sub 4-d} (Ln = La, d = 1/3; Ln = Pr, Nd, Sm, Eu, Gd, d = 1/2). The Nd{sub 2}CuO{sub 4-type} (T{prime}-phase) La{sub 2}CuO{sub 4+d} is observed after reoxidation of La{sub 2}CuO{sub 3.67} below 500C. The magnetic properties of T/O (K{sub 2}NiF{sub 4-type}) La{sub 2}CuO{sub 4} behaves differently compared with solid-state-reacted La{sub 2}CuO{sub 4}. Implications of these nonsuperconducting behaviors within superconducting carrier densities are discussed from structural point of view. La{sub 2-x}M{sub x}CuO{sub 4+d} (M = Ca, Sr; x = 0.05, 0.15), synthesized by low temperature route, also contain excess O. {sup 139}La NQR of nonsuperconducting La{sub l.85}Sr{sub 0.15}CuO{sub 4.04} show metallic properties. Tolerance factor, based on ionic radii, is to describes structures of K{sub 2}NiF{sub 4} related cuprates. With anisotropic thermal motions of apical O in La{sub 2}CuO{sub 4}, we discuss the role of out-of-plane O for stabilization of cuprate structures. Magnetic phase diagram and phase separation of La{sub 2-x}Sr{sub x}CuO{sub 4+ {delta}} are reported. From Tc decrease by doping we infer localization and pair-breaking induced by doped holes. Phase separation is realized with antiferromagnetism. We also observe scaling properties of susceptibilities versus renormalized temperatures and infer the finite size effects by doped holes. {sup 139}La NQR spin-lattice relaxation are presented for La{sub 2-x}Sr{sub x}CuO{sub 4}, x = 0.02 to 0.08. The rate below {approximately}2T{sub N}(x) shows a power-law critical behavior while above it rate is exponential with a small x-dependent spin-stiffness constant. The spin-lattice relaxation arises from fluctations of staggered magnetization in locally ordered mesoscopic domains. Magnetically ordered state is not a conventional spin glass.
- Research Organization:
- Ames Lab., IA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 10143458
- Report Number(s):
- IS-T-1536; ON: DE93011359
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1 Mar 1993
- Country of Publication:
- United States
- Language:
- English
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