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36 results on '"EJ Ansaldo"'

1. Search for isovector magnetic quadrupole strength and spin-isospin correlations inNe20

Author

Achim Richter, D. Bender, S Müller, EJ Ansaldo, D Stockhausen, Chary Rangacharyulu, NL Iudice, and Fabrizio Palumbo

Subjects
Nuclear physics, Nuclear reaction, Physics, Nuclear and High Energy Physics, Angular momentum, Isovector, Isotopes of neon, Scattering, Isospin, Atomic physics, Inelastic scattering, Excitation
Abstract

In /sup 20/Ne, the isovector M2 strength distribution in the excitation region of E/sub x/ = 11--24 MeV was investigated by inelastic electron scattering. Two transitions to levels at E/sub x/ = 11.62 and 12.1 MeV were observed with strengths of B(M2,k)up-arrow = 64 +- 13 and 56 +- 13 ..mu../sub N//sup 2/fm/sup 2/, respectively. A comparison with the analogous (..pi../sup -/,..gamma..) reaction shows that orbital contributions are non-negligible in these transitions. The data are compared to model predictions.

Published
1985
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2. Magnetic phase diagram of layered cobalt dioxide LixCoO2.

Author

Mukai K, Ikedo Y, Nozaki H, Sugiyama J, Nishiyama K, Andreica D, Amato A, Russo PL, Ansaldo EJ, Brewer JH, Chow KH, Ariyoshi K, and Ohzuku T

Subjects
Cobalt chemistry, Magnetics
Abstract

The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.

Published
2007
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3. Evidence of two dimensionality in quasi-one-dimensional cobalt oxides.

Author

Sugiyama J, Nozaki H, Ikedo Y, Mukai K, Andreica D, Amato A, Brewer JH, Ansaldo EJ, Morris GD, Takami T, and Ikuta H

Abstract

The quasi-one-dimensional (Q1D) cobalt oxides A(N + 2)Co(n + 1)O(3n + 3) (A = Ca, Sr, and Ba, n = 1 - infinity) were investigated by muon-spin spectroscopy under applied pressures of up to 1.1 GPa. The relationship between the onset Néel temperature T(on)(N) and the interchain distance (d(ic)), which increases monotonically with n, is well fitted by the formula T(N)/T(N,0) = (1 - d(ic)/d(ic,o)(beta), here for T(on)(N) approximately 100 K for Ca(3)Co(2)O(6) (n = 1) and approximately 15 for BaCoCoO(3) (n = infinity at ambient P. The T(on)(N) - d(ic) curve also predicts a large dependence of Y(N) for the compounds with n > or = 5, i.e., in the vicinity of , while the compounds show only a very small effect. Indeed, our high-pressure mu(+) results show that of BaCoO(3) is enhanced by with a slope of 2.2 K(Gpa), whereas no detectable changes by P for both Ca(3)Co(2)O(6) and Sr(4)Co(3)O(9) (n = 2). This clearly confirms the role of the 2D-antiferromagnetic interaction on T(on)(N) in the Q1D cobalt oxides.

Published
2006
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4. Static magnetic order in metallic K0.49CoO2.

Author

Sugiyama J, Nozaki H, Ikedo Y, Mukai K, Brewer JH, Ansaldo EJ, Morris GD, Andreica D, Amato A, Fujii T, and Asamitsu A

Abstract

By means of muon-spin spectroscopy, we have found that K0.49CoO2 crystals undergo successive magnetic transitions from a high-T paramagnetic state to a magnetic ordered state below 60 K and then to a second ordered state below 16 K, even though K0.49CoO2 is metallic at least down to 4 K. An isotropic magnetic behavior and wide internal-field distributions suggest the formation of a commensurate helical spin density wave (SDW) state below 16 K, while a linear SDW state is likely to exist above 16 K. It was also found that exhibits a further transition at 150 K presumably due to a change in the spin state of the Co ions. Since the dependence of the internal-field below 60 K was similar to that for Na0.5CoO2, this suggests that magnetic order is more strongly affected by the Co valence than by the interlayer distance or interaction and/or the charge ordering.

Published
2006
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22. Antiferromagnetism and superconductivity in oxygen-deficient YBa2Cu

Author

Brewer JH, Ansaldo EJ, Carolan JF, Chaklader AC, Hardy WN, Harshman DR, Hayden ME, Ishikawa M, Kaplan N, Keitel R, Kempton J, Kiefl RF, Kossler WJ, Kreitzman SR, Kulpa A, Kuno Y, Luke GM, Miyatake H, Nagamine K, Nakazawa Y, Nishida N, Nishiyama K, Ohkuma S, Riseman TM, Roehmer G, Schleger P, Shimada D, Stronach CE, Takabatake T, Uemura YJ, Watanabe Y, Williams DL, Yamazaki T, and Yang B

Published
1988
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