NMR Measurements of Intrinsic Spin Susceptibility in LaFeAsO0.9F0.1

We will probe the intrinsic behavior of spin susceptibility χ spin in the LaFeAsO 1- x F x superconductor ( x ∼0.1, T c ∼27 K) using 19 F and 75 As NMR techniques. Our new results firmly establish a pseudo-gap behavior with Δ PG / k B ∼140 K. The estimated magnitude of χ spin at 290 K, χ spin ∼1.8 ×10 -4 emu/mol-Fe, is approximately twice larger than that in high T c cuprates. We also show that χ spin levels off below ∼50 K down to T c .