ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
The double-perfect-crystal small-angle diffraction technique enables measurement of scattering angles to within an accuracy of 0.3′′ of arc. At a wavelength of 2.55 Å, this provides a resolution of 3 × 10−6 Å−1 in the scattering vector. This technique has been used to study the anisotropic behavior of the critical parameters B0 and Hc1, characteristic of the first-order magnetic phase transition which occurs in low-κ type II superconductors. Magnetic fields were applied parallel to several crystal axes in the (1{\bar 1}0) and (100) planes of a large single-crystal sphere of pure niobium, resulting in well defined flux-line lattices (FLL). Measurement of the FLL cell area in the intermediate, mixed-state-field region gives the equilibrium flux density B0, which results from an attractive interaction between fluxoids. In addition, field variation of the scattered neutron intensity allows measurement of the transition field between the mixed state and intermediate mixed state. This transition field is related to the lower critical field Hc1 and enables its determination to a precision of 0.2%. Data at T = 4.3 K display a small anisotropic effect of about 2% in B0 and 1% in Hc1. Although orientation effects of this magnitude are difficult to resolve by bulk measurements, the neutron data are in accord with magnetization data. The temperature dependence of these parameters is found to be in qualitative but not quantitative agreement with current theoretical models.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889878014144
Permalink
