Measurements of the elliptic flow, v , of identified hadrons (π , K , Ks0, p, p̄, φ, Λ, Λ̄, Ξ , Ξ , Ω , Ω ) in Au+Au collisions at √s =7.7, 11.5, 19.6, 27, 39, and 62.4 GeV are presented. The measurements were done at midrapidity using the time-projection chamber and the time-of-flight detectors of the Solenoidal Tracker at RHIC experiment during the beam-energy scan program at Relativistic Heavy Ion Collider. A significant difference in the v values for particles and the corresponding antiparticles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, √s (or increasing baryon chemical potential, μ ), and is larger for the baryons as compared to the mesons. This implies that particles and antiparticles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of v that was observed at √s =200 GeV. However, for the selected group of particles (π , K , Ks0, p, Λ, Ξ , Ω ) NCQ scaling at (m -m )/n >0.4 GeV/c2 is not violated within ±10%. The v values for φ mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured p values. © 2013 American Physical Society. 2 NN 2 NN B 2 NN T 0 q 2 T ± ± - ̄+ - ̄+ + + - -