The origin of nematic order remains one of the major debates in iron-based
superconductors. In theories based on spin nematicity, one major prediction is
that the spin-spin correlation length at (0,π) should decrease with
decreasing temperature below the structural transition temperature Ts. Here
we report inelastic neutron scattering studies on the low-energy spin
fluctuations in BaFe1.935Ni0.065As2 under uniaxial pressure. Both
intensity and spin-spin correlation start to show anisotropic behavior at high
temperature, while the reduction of the spin-spin correlation length at
(0,π) happens just below Ts, suggesting strong effect of nematic order
on low-energy spin fluctuations. Our results favor the idea that treats the
spin degree of freedom as the driving force of the electronic nematic order.Comment: 5 pages, 4 figure