Doping Experiments on Low-Dimensional Oxides and a Search for Unusual Magnetic Properties of MgAlB₁₄

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 2002

DOI:https://doi.org/10.2172/806588· OSTI ID:806588

Hill, Julienne Marie ^[1]

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1. Iowa State Univ., Ames, IA (United States)

Doping experiments on La₂CuO₄, Sr₂CuO₃ and SrCu₂(BO₃)₂ were performed with the intent of synthesizing new metallic low-=dimensional cuprate oxide compounds. Magnetic susceptibility χ(T) measurements on a polycrystalline La₂CuO₄ sample chemically oxidized at room temperature in aqueous NaClO showed superconductivity with a superconducting transition temperature T_c of 42.6 K and a Meissner fraction of 26%. They were unable to electrochemically oxidize La₂CuO₄ in a nonaqueous solution of tetramethylammonium hydroxide (TMAOH) and methanol. Sr₂CuO₃ was found to decompose upon exposure to air and water. Electron paramagnetic resonance, isothermal magnetization M(H), and χ(T) measurements on the primary decomposition product, Sr₂Cu(OH)₆, were consistent with a nearly isolated, spin S = 1/2, local moment model for the Cu⁺² spins. From a fit of χ(T) by the Curie-Weiss law and of the M(H) isotherms by a modified Brillouin function, the weakly antiferromagnetic exchange interaction between adjacent Cu⁺² spins in Sr₂Cu(OH)₆ was found to be J/k_B = 1.06(4) K. Doping studies on SrCu₂(BO₃)₂ were inconclusive. χ(T) measurements on an undoped polycrystalline sample of SrCu₂(BO₃)₂, a sample treated with distilled water, and a sample treated with aqueous NaClO showed no qualitative differences between the samples. In addition, χ(T) and M(H, T) studies of the ultra-hard material MgAlB₁₄ were carried out in search of superconductivity or ferromagnetism in this compound. χ(T) measurements on a powder sample revealed temperature-independent diamagnetism from 1.8 K up to room temperature with a Curie-Weiss impurity concentration equivalent to ~ 1 mol% of spin-1/2 ions. In contrast, M(H, T) data on hot pressed samples showed evidence of ferromagnetic transitions above ~ 330 K. Scanning electron microscopy and Auger microprobe analysis of the hot pressed samples indicated that the observed ferromagnetism was likely due to Fe impurities.

• Research Organization: Ames Lab., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (US)
• DOE Contract Number: W-7405-Eng-82
• OSTI ID: 806588
• Report Number(s): IS-T 2066; TRN: US0301336
• Resource Relation: Other Information: TH: Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); PBD: 31 Dec 2002
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CURIE-WEISS LAW
DIAMAGNETISM
ELECTRON SPIN RESONANCE
EXCHANGE INTERACTIONS
FERROMAGNETISM
HYDROXIDES
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
OXIDES
SCANNING ELECTRON MICROSCOPY
SUPERCONDUCTIVITY
TRANSITION TEMPERATURE