Publications


PHASE-DIAGRAM STUDIES AND CRYSTAL-GROWTH OF PRBA2CU3O7-Y

PHYSICA C 214 (1993) 231-238

CK CHEN, AT BOOTHROYD, YL HU, FR WONDRE, BM WANKLYN, JW HODBY


Pressing for better results

Nature 364 (1993) 286-287

PG Radaelli, JD Jorgensen


STRUCTURE, DOPING AND SUPERCONDUCTIVITY IN HGBA2CACU2O6+DELTA (TC-LESS-THAN-OR-EQUAL-TO-128-K)

PHYSICA C 216 (1993) 29-35

PG RADAELLI, JL WAGNER, BA HUNTER, MA BENO, GS KNAPP, JD JORGENSEN, DG HINKS


The irreversibility line of HgBa<inf>2</inf>CuO<inf>4+δ</inf>

Applied Physics Letters 63 (1993) 693-695

U Welp, GW Crabtree, JL Wagner, DG Hinks, PG Radaelli, JD Jorgensen, JF Mitchell, B Dabrowski

Using magnetization hysteresis loops we have determined the irreversibility line of polycrystalline samples of HgBa2CuO4+δand Hg0.8Pb0.2Ba2CuO4+δ. The irreversibility line is found at rather high temperatures. It does not show the drastic depression with increasing temperature as is observed in highly anisotropic Bi/Tl-based CuO superconductors. At 77 K the irreversibility field is around 0.3 T, which is substantially higher than in Bi2Sr2CaCu2O8and Bi2Sr2Ca2Cu3O10. The advantages of this material for large-scale applications are outlined.


SUPERCONDUCTIVITY - PRESSING FOR BETTER RESULTS

NATURE 364 (1993) 286-287

PG RADAELLI, JD JORGENSEN


STRUCTURE OF THE SUPERCONDUCTING LA2CUO4+DELTA PHASES (DELTA-APPROXIMATE-TO-0.08,0.12) PREPARED BY ELECTROCHEMICAL OXIDATION

PHYSICAL REVIEW B 48 (1993) 499-510

PG RADAELLI, JD JORGENSEN, AJ SCHULTZ, BA HUNTER, JL WAGNER, FC CHOU, DC JOHNSTON


Structure and superconductivity of HgBa<inf>2</inf>CuO<inf>4+δ</inf>

Physica C: Superconductivity and its applications 210 (1993) 447-454

JL Wagner, PG Radaelli, DG Hinks, JD Jorgensen, JF Mitchell, B Dabrowski, GS Knapp, MA Beno

We have used neutron powder diffraction to investigate the defect structure of HgBa2CuO4+δ. An interstitial oxygen defect in the Hg plane is the primary doping mechanism. A superconducting transition temperature, Tc onset, of 95 K is achieved when ≈0.06 oxygen atoms per formula unit are incorporated at this site by annealing the sample at 500°C in pure oxygen. Annealing in argon at 500°C lowers the oxygen content in this site to ≈0.01 and results in a Tcof 59 K. The neutron powder diffraction data give evidence for a second defect in the Hg plane which we conclude involves the substitution of copper for about 8% of the mercury and the incorporation of additional oxygen (≈0.1 atoms per formula unit), presumably bonded to the copper defects. In the present samples, the concentration of this defect does not vary with synthesis conditions and its contribution to doping is, therefore, unclear. The structure of the compound is the same at room temperature and superconducting temperatures. © 1993.


POLARIZED NEUTRON REFLECTION AS A PROBE OF INPLANE MAGNETIZATION VECTOR ROTATION IN MAGNETIC MULTILAYERS

J MAGN MAGN MATER 121 (1993) 185-188

SJ BLUNDELL, JAC BLAND


Neutron ellipsometry

Journal of Magnetism and Magnetic Materials 125 (1993) 69-77

JAC Bland, HP Hughes, SJ Blundell, NF Johnson

We discuss the similarities which exist between the reflection of neutrons from ferromagnetic media and the reflection of light from media rendered gyrotropic by the application of a magnetic field, and show that the vector character of the neutron polarisation can be fully exploited in spin-analysed neutron reflection measurements (termed 'neutron ellipsometry' because of the similarity to optical ellipsometry) to give valuable magnetometric information for ultrathin films and multilayers, and with certain advantages over conventional polarised neutron reflection measurements. We show that for the case of a single ultrathin magnetic layer with uniform magnetisation, the component of the in-plane magnetisation perpendicular to the incident neutron polarisation determines both the spin conserving and spin flipping reflectivities in the region of total reflection, while a more complex regime obtains in the partially reflecting region. Making neutron ellipsometric measurements in both reflection regions thus allows the magnitude and orientation of the in-plane magnetisation vector to be directly determined. This is illustrated by numerical calculations for a single ultrathin iron layer supported by a silver substrate and with a silver cap. © 1993.


The Phase Diagram and Crystal Growth of Y1–xPrxBa2Cu3O7–y

J Crystal Growth Elsevier 128 (1993) 767-771

C Chen, H Yongle, BM Wanklyn, S Hazell, AK Pradhan, JW Hodby, AT Boothroyd, FR Wondre

Y1xPrx)Ba2Cu3O7-y is a unique superconductive material for the investigation of the interrelation between crystal structure, chemical composition and physical properties. In order to grow large crystals of high quality, an extensive study has been made of the Y2O3-Pr6OI1-BaO-CuO growth system. The eutectic composition of the BaO-CuO flux is confirmed by the improved thermogravimetric method (ITGA) as occurring at the molar composition of 7:18. The pseudo-binary phase diagram of (Y, Pr)BCO-(7BaO+18CuO) has been determined by means of differential thermal analysis (DTA), by X-ray diffraction and by study of crystal growth. Using the phase diagram, suitable compositions and temperature programs have been established for the growth of large crystals and for the separation of the crystals from the flux. Single crystals with a wide range of Pr doping have been obtained from a eutectic BaO-CuO flux. The dependence of the Pr concentration in the crystals on the composition of the initial melt has been determined by electron probe microanalysis and X-ray microanalysis. The superconducting transition temperature is found to decrease monotonically with increasing Pr concentration.


Magnetic coupling in Fe/Cr/Fe sandwich structures directly observed by polarised neutron reflection

Journal of Magnetism and Magnetic Materials 123 (1993) 320-324

JAC Bland, RD Bateson, NF Johnson, SJ Blundell, VS Speriosu, S Metin, BA Gurney, J Penfold

We have used polarised neutron reflection to directly determine the vector orientation of the individual Fe layer average magnetisations in an antiferromagnetically coupled 50 ÅFe/15 ÅCr/50 ÅFe sandwich structure prepared by sputtering. The spin dependent neutron wave in the multilayer structure is represented by a two component spinor and the resulting reflected intensity is found to be highly sensitive to variations in the orientations of the layer-dependent magnetisation vectors, permitting the preferred orientation of the average magnetisation in each Fe layer to be studied. The saturated state is found to correspond to a uniform ferromagnetic alignment of the Fe layer magnetisations. At low field, we are able to assess the degree to which the magnetic alignment is fully antiparallel, and conclude that our results are consistent with the development of a multidomain structure. © 1993.


TEMPERATURE COEFFICIENTS FOR THE CHAIN DIMENSIONS OF POLYSTYRENE ANDPOLYMETHYLMETHACRYLATE

JOURNAL OF CHEMICAL PHYSICS 99 (1993) 9135-9144

AT BOOTHROYD, AR RENNIE, GD WIGNALL


Structure, doping and superconductivity in HgBa<inf>2</inf>CaCu<inf>2</inf>O<inf>6+δ</inf>(T<inf>c</inf>≤ 128 K)

Physica C: Superconductivity and its applications 216 (1993) 29-35

PG Radaelli, JL Wagner, BA Hunter, MA Beno, GS Knapp, JD Jorgensen, DG Hinks

We have studied the defect structure and superconducting propertiess of HgBa2CaCu2O6+δby neutron powder diffraction, AC susceptibility and DC resistivity. An as-synthesized sample has an onset Tcof 128 K, the highest yet reported for this material. The critical temperature decreases slightly (126 K) after oxygenation, and drops to 92 K after reduction in flowing argon. Neutron diffraction data give evidence that the primary doping mechanism in this material is provided by oxygen atoms in an interstitial position, similar to the case of the one-layer compound HgBa2CuO4+δ. The occupancy of this site varies from 0.08 (1) for the argon-reduced sample to 0.22 (1) for the oxygenated sample. Unlike the case of the one-layer compound, no evidence of an additional defect site was found in these samples. HgBa2CaCu2O6+δhas remarkably long copper-apical oxygen distances and almost perfectly flat CuO2planes. © 1993.


THE MAGNETIC STATE OF PR IN PRBA2CU3O7

PHYSICA C 217 (1993) 425-438

AT BOOTHROYD, SM DOYLE, R OSBORN


STRUCTURE INDUCED MAGNETIC-ANISOTROPY BEHAVIOR IN CO/GAAS(001) FILMS

J APPL PHYS 73 (1993) 5948-5950

SJ BLUNDELL, M GESTER, JAC BLAND, C DABOO, E GU, MJ BAIRD, AJR IVES


Structure of superconducting Sr0.9La0.1CuO2 (Tc=42 K) from neutron powder diffraction.

Phys Rev B Condens Matter 47 (1993) 14654-14656

JD Jorgensen, PG Radaelli, DG Hinks, JL Wagner, S Kikkawa, G Er, F Kanamaru


THE DIRAC COMB AND THE KRONIG-PENNEY MODEL - COMMENT ON SCATTERING FROM A LOCALLY PERIODIC POTENTIAL

AMERICAN JOURNAL OF PHYSICS 61 (1993) 1147-1148

S BLUNDELL


SINGLE-CRYSTAL GROWTH OF BI2SR2CACU2O8 USING AN INFRARED IMAGE FURNACE

PHYSICA C 206 (1993) 148-154

G BALAKRISHNAN, DM PAUL, MR LEES, AT BOOTHROYD


NEUTRON-SCATTERING STUDY OF THE ELECTRON PHONON INTERACTION IN SUPERCONDUCTING NIOBIUM

PHYSICA B 180 (1992) 348-350

AT BOOTHROYD, WG STIRLING, R CURRAT, NR BERNHOEFT, DMK PAUL, SI SHIHUB


Crystal-field excitations in Nd2CuO4, Pr2CuO4, and related n-type superconductors.

Phys Rev B Condens Matter 45 (1992) 10075-10086

AT Boothroyd, SM Doyle, DM Paul, R Osborn

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