Scanning Hall-Probe Microscopy of a Vortex and Field Fluctuations in La _1.85 Sr _0.15 CuO ₄ Films

Abstract

A high-resolution scanning Hall-probe microscope is used to spatially resolve vortices in high-temperature superconducting Lal,aSro,,jCu04 films. At low magnetic fields, a disordered vortex arrangement is observed. A fit to the surface field of an individual vortex is consistent with one flux quantum, and is used to determine the local penetration depth and its temperature dependence. At higher fields, magnetic fluctuations are observed and compared to a collective pinning model. For films grown with the c-axis tilted from the surface normal, oval vortices are observed.

An interchangeable scanning Hall probe/scanning SQUID microscope

“…Suppose that the origin of the coordinate system is at the center of the vortex on the film surface, the z-component of the field distribution of a vortex at a position z above the film surface is defined as B z (x, y, z). In the limit of x 2 + y 2 + z 2 λ, B z can be expressed as 4,28,29 B z (x, y, z) = 0 2π…”

Local magnetic probes of superconductors

“…For a thin superconducting ® lm it can be shown that the¯ux distribution a height z above the sample surface is given by (Chang et al 1992b) where k g = (g 2 + 1/¸2) 1/ 2 , z is measured from the centre of the ® lm of thickness d and¸is the bulk penetration depth. This expression has been convoluted with the numerical Hall probe response function and ® tted to line scans through the centre of the numbered vortices to establish a value of¸for each vortex.…”

Cryogenic scanning Hall-probe microscope with centimeter scan range and submicron resolution

“…A vortex is a spatially sharp magnetic object whose field is well modeled. [17][18][19] Our sample is a film of YBCO, a well-studied material. 20…”