Magnetism near Vortex Cores of Cuprate Superconductors

We examined muon-spin-resonance ($\mu $SR) vortex data of Bi2212, Tl2223, and YBCO to search for antiferromagnetism (AF) near the vortex cores. [1] Field distributions were obtained from $\mu $SR data using Maximum-Entropy analysis. The grainboundary and vortex signals were fitted by Gaussian and Lorentzian curves, the latter suggestive of extra AF ordering. Narrow Gaussians fit the grainboundary signals well, independent of temperature. For T $<$ 0.4T$_{c}$, Lorentzians fit much better than Gaussians on the high-field side associated with the vortex core. Such results suggest that magnetism exists near the vortex cores. [1,2] The field dependence of the YBCO AF Lorentzian width is discussed. An AF presence near vortex cores supports theories that predict spin ordering for cuprate superconductivity. Research supported by REU-NSF, WiSE@SJSU {\&} SJSU College of Science. [1] J. Lee \textit{et al}, J Appl Phys 95 (2004) 6906, and \textit{Virtual J Appl of Superconductivity, June 2004 V6 Issue11;} K Prudchenko \textit{et al}, \textit{www.jyi.org/volumes/volume10/issue6/articles/prudchenko.html} [2] C. Boekema \textit{et al}, Int J Modern Phys B17 (2003) 3436.