Magnetic form factor of URu₂Si₂

We report the field-induced magnetic form factor of the heavy-electron system URu₂Si₂ obtained by using polarized neutrons. The neutron experiments were performed on the two single crystals at 60 K by applying a magnetic field of 6 T along the tetragonal c-axis. The observed magnetic form factor is close to the theoretical 5f form factor of the free U^{3 +} or U^{4 +} ions calculated by the dipole approximation as other U-based intermetallic superconductors. However, the extrapolated value at sin θ / λ = 0 ( 0.07 μ_B / U ) is smaller than the bulk magnetization value ( 0.10 μ_B / U ). Therefore, this result indicates some contribution other than 5f electrons to the bulk magnetization of URu₂Si₂.