Lower critical field measurements in YBa2Cu3O(6+x) single crystals

The temperature dependence of the lower critical field in YBa2Cu3O(6+x) single crystals was determined by magnetization measurements with the applied field parallel and perpendicular to the c-axis. Results are compared with data from the literature and fitted to Ginzberg-Landau equations by assuming a linear dependence of the parameter kappa on temperature. A value of 7 plus or minus 2 kOe was estimated for the thermodynamic critical field at T = O by comparison of calculated H (sub c2) values with experimental data from the literature

Measurement of H(sub c1) in a single crystal of YBa2Cu3O7 with low pinning

The measurement of H(sub c1) in barium yttrium copper oxide (BYCO) is often ambiguous because the presence of large pinning forces makes it difficult to discern exactly where the first deviation from linearity occurs. In addition there are complications because demagnetizing factors are often not well known. By utilizing a single crystal of YBCO with a nearly cubic shape, the uncertainty in the demagnetizing factor was minimized. In addition, the crystal used exhibited a very small amount of pinning with H applied perpendicular to the c axis, and a sharp break in the initial magnetization vs. field curve could be observed over a wide range of temperature. This allowed a precise determination of H(sub c1). The measured values of H(sub c1) could be well described by the Abrikosov relation with a Ginzburg-Landau parameter which varied linearly with temperature

Magnetic hyperfine field structure of iron Urushibara type catalysts

We have utilized the Mössbauer effect to study the hyperfine field structure of iron Urushibara catalysts. The Mössbauer spectra of those catalysts prepared using zinc show that they consist of a mixture of magnetic and non‐magnetic Fe‐Zn alloys. Both the magnetic field distribution in the magnetic phase and the relative amounts of magnetic and non‐magnetic phases depend on the Fe‐Zn ratio used in the preparation of the catalyst. This dependence on Fe–Zn ratio is in contrast to iron Urushibara catalysts prepared using aluminum (and Raney iron type catalysts) in which the active phase is almost pure α‐fe, irrespective of the Fe‐Al ratio. The activity of zinc prepared iron Urushibara catalysts for certain hydrogentation reactions is known to be greater than that of aluminum prepared iron Urushibara catalysts and the above results suggest a relationship between activity and the modification of the iron catalyst by alloyed zinc. The alloying behavior of the Fe‐Zn particles may be analogous to that of the so‐called bimetallic clusters observed in other alloy systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87521/2/391_1.pd

The NBS: Processing/Microstructure/Property Relationships in 2024 Aluminum Alloy Plates

As received plates of 2024 aluminum alloy were examined. Topics covered include: solidification segregation studies; microsegregation and macrosegregation in laboratory and commercially cast ingots; C-curves and nondestructive evaluation; time-temperature precipitation diagrams and the relationships between mechanical properties and NDE measurements; transmission electron microscopy studies; the relationship between microstructure and properties; ultrasonic characterization; eddy-current conductivity characterization; the study of aging process by means of dynamic eddy current measurements; and Heat flow-property predictions, property degradations due to improve quench from the solution heat treatment temperature

Supertransferred Hyperfine Fields at Sb5+ in Insulating Ferrites: Effects of Local Order and Ion‐Specific Properties

The supertransferred hyperfine fields at Sb5+ in LiFe5O8LiFe5O8, CoFe2O4CoFe2O4, and YIG have been determined using Sb Mössbauer spectroscopy. In contrast to CoFe2O4CoFe2O4, NiFe2O4NiFe2O4, and YIG, the small, average hyperfine field of ∼100 kOe at Sb5+ in LiFe5O8LiFe5O8 requires the existence of significant local order and indicates that the clustering of Li1+ about Sb5+ is approximately ten times as large as that expected for a random intrasite cation distribution, in agreement with the known strong influence of Sb substitution in destroying the Li:Fe ordering. The decrement in the hyperfine field at Sb5+ due to an A‐site Co2+ is also found to be larger than that due to Ni2+.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87642/2/518_1.pd