Observation of Magnetic Order in a ${\rm YBa_2Cu_3O_{6.6}}$ Superconductor

Abstract

Polarized beam neutron scattering measurements on a highly perfect crystal of ${\rm YBa_2Cu_3O_{6.6}}$ show a distinct magnetic transition with an onset at about 235K, the temperature expected for the pseudogap transition. The moment is found to be about 0.1 $μ_B$ for each sublattice and have a correlation length of at least 75 à . We found the critical exponent for the magnetic neutron intensity to be 2$β$ =0.37$\pm$ 0.12. This is the proper range for the class of transition that has no specific heat divergence possibly explaining why none is found at the pseudogap transition.

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